Experience in a Book
Engine Maintenance (continued)

TAPPET NOISE: Roger Bywater of AJ6 Engineering and formerly with Jaguar engine development, says, "In fact a recognised source of tappet noise on the V12 is excessive side clearance of the tappet in the aluminium carrier allowing it to ërattle about'. Remember the XK used cast iron tappet sleeves and they expand and contract at the same rate as the tappet so the clearance remained more or less constant. This does not happen on the V12 and the minimum diametral clearance is set by the need for a top size (high limit of tolerance band) tappet to not jam in a bottom size carrier bore at minus 40 degrees in a Canadian Winter. The other extreme of a bottom size tappet in a top size bore could well be quite sloppy when fully warm and the way the cam moves it around can be very critical. Cam profile, tappet clearance, side movement, rotation and rock-over at peak lift, as well as valve seating geometry, all come into what is actually quite a complex phenomenon. For the record the range of diametral tappet clearances involved run from about 0.0005" to about 0.002" at room temperature. I wonder how many engine builders have even thought about measuring such things?"

TAPPET BLOCK REMOVAL: Sections 12.13.29 and 12.13.30 of the Repair Operation Manual describe how to remove the tappet blocks, and both procedures end with "Lift off tappet blocks carefully, retrieve tappets and valve adjusting pads." The Haynes manual provides a similar procedure. Both make it clear that the tappets must be reinstalled in the same locations they came out of, but if you yank that tappet block as described I dunno how you'll avoid having tappets everywhere. If you have a decent magnet on hand, it might be a better idea to use it to remove the tappets before unbolting the tappet block from the head. If you don't have a magnet, you might want to at least use a magic marker to mark the tappets before disassembly.

Sidetrack: If you need some really good magnets, tear apart a scrapped computer hard drive.

When reinstalling the tappet block, the manuals say you should tighten the bolts and nuts in order, but don't specify a torque. Later on, you'll be installing the bearing caps on the camshaft, and there is a max torque value specified there -- 9 lbf.ft. or 1,24 kgf.m. Since the nuts are the same size and all actually hold the tappet block to the head, it might make sense to tighten all of these nuts to the same specified torque. However, the fact that the cam bearing cap torque spec is a max rather than a range, plus that it's rather low for a 5/16" nut, indicate that this value is specified in order to prevent distortion to the soft aluminum bearing caps and probably isn't valid for the other tappet block fasteners. Hence, it may make more sense to use torque values specified for other typical 5/16" UNF nuts -- typically 11-13 lbf.ft. or 1,52-1,80 kgf.m. Later, while torquing down the cam bearing caps, you might wanna go back and retorque these other nuts and screws.

The upper row of fasteners on the tappet block are different, though. If the car is a pre-ë84, they are a coarse thread rather than a fine thread, so the torque values aren't necessarily equal. The objective should be to achieve the same bolt tension, but the difference in threads means it will take a different torque to achieve the same tension. Judging from other similar applications, it appears that coarse thread fasteners should be tightened to a slightly higher torque than fine thread, so torquing these to perhaps 12-15 lbf.ft would be in order.

They are also socket head cap screws, meaning that it requires an Allen wrench to tighten or loosen them. Loosening is no problem, but tightening to a specified torque with an Allen wrench is tricky since you can't put your torque wrench on it. There are a handful of options, though. First and most properly, you can find a tool that looks like a short hex key built into a socket so it can be attached directly to a ratchet or torque wrench. These are fairly common, but the size needed here -- 7/32" -- is not quite so common. Sometimes you need to buy an entire set of these tools to get the one you need, and you are hereby advised that many such sets don't have the one you need! Be sure to check before buying. Discount Auto Parts sells a pack of four such tools on a card labelled "Brake Caliper Hex Bit Set" by Performance Tool, and one of the four is the 7/32" you need. These are really heavy-duty to fit 3/8" drive ratchets (most of these type tools fit 1/4" drive ratchets) and have an unconditional lifetime warranty.

Another option is to check for bits for electric screwdrivers. These bits are 1/4" hex shafts about 2" long to fit in the chuck of an electric screwdriver or drill, and there are all kinds of tips to drive almost anything. If you can find a bit with a 7/32" hex tip on it, you can put it into the head of the bolt and drive it with a torque wrench connected to a 1/4" socket. Unfortunately, finding this particular type bit may prove a little difficult.

A third possibility is to cut a piece off the end of your 7/32"Allen wrench, stick it in the bolt head, and drive it with a torque wrench connected to a 7/32" socket. This makes for a really flimsy assemblage of tools, but it should work OK. Don't drop that little hex piece!

These cap screws don't have any lock washers under the heads, since a lock washer wouldn't fit down in the hole. This doesn't seem to pose a problem, however; there are no reports of these bolts backing out.

Good luck torquing the bearing cap nuts to 9 lbf.ft. with a 150 lbf.ft. torque wrench, which is the only thing available at most auto parts stores. J. C. Whitney offers a torque wrench with a 0-600 in.-lbs. (0-691 cm-kgs.) range, catalog number 15xx01148.

TAPPET BLOCK SEALING: There is no gasket between the tappet block and the head. Although this joint must be sealed to prevent oil leaks, perhaps Jaguar felt that the camshaft support and the valve clearances would not be secure enough with a gasket underneath the whole assembly.

So, how do we seal it? The early (©1975) Repair Operation Manual, sections 12.13.29 and 12.13.30, says "Smear mating surfaces of tappet block and cylinder head with Hylomar." Michael Neal says, "Hylomar is a sealant that does not harden over time. It is still readily available and is blue in color. It is commonly used to seal the liners into the V12 motor and the cam towers to the heads. I've stopped using it to seal the cam towers because a good blast of carb cleaner or an aggressive steam cleaning can dislodge it and cause an oil leak that leaks directly onto the exhaust manifolds. Not only does an oil leak like this make a mess but it also causes the exhaust manifold gaskets to erode."

The Haynes manual merely says to use "jointing compound", perhaps recognizing the shortcomings of Hylomar for this application. According to Craig Sawyers, his repair manual (Jaguar SIII Service Manual, published by Jaguar, AKM 9006 Ed 5, copyright Jaguar Cars Ltd 1988) "...says to use Loctite 573. I used 574, which the Loctite website (www.loctite.com) has as practically the same stuff. TWR Jaguar in Oxford (ie Tom Walkinshaw's dealership, who manufactured the XJ220. I believe they know a thing or two about Jags) use 574."

A call to Loctite (1-888-LOCTITE) and a discussion with a tech rep revealed the following: First off, Hylomar (which is also made by Loctite, under license from Marston Bentley Ltd.) is intended as a gasket dressing, not to be used without a gasket at all, and is not recommended for this application. As Sawyers says, either 573 or 574 is suitable; the chief difference is in difficulty of disassembly, since 574 will glue the parts together pretty well while 573 is designed to be easier to get apart.

Unfortunately, neither 573 or 574 is commonly sold in auto parts stores. Finding it will normally entail calling Loctite at the above number and getting the name and number of a local distributor; Loctite will not sell it direct.

Sawyers reports that you'll need about 50ml to do both banks. 573 in a 50ml tube is Loctite part number 21455 and 574 in a 50ml tube is part number 24018. Neither of the substances is cheap, but worse yet you may end up facing a minimum order requirement of 10 tubes or some such, so you might want to talk your local Jag club into placing an order for the group.

573 is bright flourescent green and 574 is orange.

Think a little bit before applying this stuff. There is no need to smear it all over everywhere, and in fact that type of application is not recommended because it can result in air bubbles. You also don't want to get any inside the tappet guides. The instructions on the tube of 573 say to apply a bead to one part only, which makes it easier to apply than Hylomar; trying to "smear" it onto the head itself would be tricky since all those studs are in the way. Basically, you need to apply one continuous bead of sealant completely around the edge of the tappet block, making sure the bead is always positioned so it will contact a mating surface on the head (some flat areas on the tappet block correspond to gaping holes on the head).

Now, think a little more before applying this stuff. Note that the bead should divert to just inside of each of the 10 holes (one row of 6 plus the 4 surrounding the sprocket) for the studs on which the nuts are located outside the cam cover. Unfortunately, depending on the casting tolerances of your particular tappet block, the amount of surface area just inside the 6 holes may be tiny indeed; you will need to exercise considerable care to make sure that particular location seals properly when assembled. Also note that the bead must be located outside of the other 20 holes, otherwise oil might get under a nut, run down a stud and leak out; a serious potential on the studs that hold the cam bearing caps, since oil is being fed between those parts.

If all that wasn't perfectly clear, I have provided an illustration showing where that bead of sealant should be located; see Figure 3.

If you have a pre-'84 car with 5/16" studs, the 4 studs surrounding the cam sprocket appear to have been sealed with cap nuts and copper washers. However, if the bead of sealant is applied to the tappet block correctly inward of these studs and the cam cover gasket does its job, there will be nothing within these stud holes to leak. From '84 on, these 4 studs are metric and use normal nuts and spiral groove washers with no attempt at sealing the studs, so they must have figured out it wasn't necessary.

VALVE CLEARANCES: There's good news and bad news. The bad news is that, in order to adjust the valve clearances, you must tear a considerable amount of hardware off the top of the engine. Also, since adjustment is via shims, the measurements must be made, the assembly torn apart and the shims removed and replaced, and the gaps checked again after reassembly. The shims themselves cost about $3 each. Having a dealer perform this work reportedly costs over $600, and is probably a reasonable charge considering the number of hours that will be required. Before doing the work yourself, see the tip on clearing off the top of the engine. Also see the tip on valve clearances.

The good news is that this adjustment almost never needs to be done; the engine often can go the life of the car and these gaps will still be within tolerances. In fact, if your valves require adjusting, it is recommended that the camshafts, tappet blocks, tappets, and valves and seats themselves be checked for damage.

A minor tip: The valve adjusting pads come in sizes varying in .001" increments and (the genuine Jaguar parts anyway) indicated by a letter etched on one side of the pad. As a favor to the next guy who'll be working on this engine, install the pads with the letter facing outward (toward the tappet). Years later, the letter will still be legible. If installed with the letter facing the end of the valve, it will be difficult or impossible to decipher the letter later on.

CYLINDER HEAD REMOVAL: First, a bit of clarification: It is possible to remove each head with the camshaft and tappet block in place, and this may make sense if the reason for disassembly is farther down. This is the procedure outlined in both the Repair Operation Manual and the Haynes manual. On the other hand, if you plan to work on the tappets or valves anyway, you might choose to remove the camshaft and tappet block before removing the head. It makes the head lighter for lifting, and it makes it safer to set down -- there won't be any valves sticking out the bottom.

The following are a few comments/corrections to the Repair Operation Manual, Sections 12.29.11 and 12.29.12, along with corresponding sections of the Haynes manual. You might want to scribble notes in the margins of your books.

In Section 12.29.11, which is about pulling the B bank head, step 19 deals with moving the transmission dipstick tube outta the way. The dipstick for the BW tranny is on the B side, but on the cars with the GM400 the dipstick is over on the A side, so this step needs to be moved to Section 12.29.12. The same thing might be said of step 14 in Chapter 1, Section 19 of the Haynes manual -- that it should be moved to Section 20 -- but if you have a later car, you should probably be following the procedures outlined in Chapter 13, Section 3 anyway.

In Section 12.29.12, which is about pulling the A bank head, step 5 says to remove the auxiliary air valve. The auxiliary air valve is on the B side, and doesn't need removal for working on the A head only. The same correction applies to Chapter 1, Section 20, step 5 in the Haynes manual.

Steps 8 and 12 in section 12.29.11 and steps 10 and 14 in section 12.29.12 instruct you to position the engine at TDC on cylinder 1A (by using the cam aligning tool on the notches in the camshafts) and then unbolting the sprockets from the camshafts. You will find this job goes easier if beforehand you rotate the crank one full revolution from that position (TDC on cylinder 6A, notches on cams pointing downward towards the head) and pull two bolts and one tablock off of each sprocket. They're easier to get to when pointing up than when pointing down. Step 7 of Section 12.13.01 and step 6 of Chapter 1, Section 10 of the Haynes manual hint in this direction without making it as clear as they might.

Both manuals talk about removing heat shields, but beyond the big obvious one on each side don't really clarify what they're talking about. In all probability they're referring to the heat shield on the downpipe on the LH side as well as the heat shields around the boots on the power steering rack. The heat shields on the rack need to be removed in order to deal with the downpipes.

Neither manual even mentions the front exhaust manifolds. It's probably a matter of choice; they can either come off with the head or separately. If left attached to the head, they provide a nice handle for grabbing, but they do make the assembly heavier to lift.

CYLINDER HEAD REMOVAL -- ENGINE IN CAR: The conundrum facing anyone pulling the heads with the engine in the car is the fact that the rear exhaust manifold on each side is too close to a section of the chassis. If the head is slid up the studs with the rear manifold still bolted to it, it will hit the chassis long before the head clears the studs. This problem can be addressed in two ways: 1) the rear manifolds can be removed from the head first; or 2) the motor mounts can be disconnected and the engine moved around until the manifolds clear the chassis as the head comes off. Sections 12.29.11 and 12.29.12 of the Repair Operation Manual use the first option. Section 12.29.12 for the A bank head also describes pulling the starter, which is probably entirely to gain access to the lower nuts on the rear exhaust manifold on that side.

Despite the ease of removing these manifolds indicated in the manual, if you choose the option of removing the manifolds first you'll run into the same problem -- the chassis is too close. The manifold won't come over its own studs without hitting the chassis first. Of course, sections 30.15.10 and 30.15.11 of the Repair Operation Manual just give the step-by-step instructions as though you will have no trouble. We won't even get into how much fun you'll have getting a wrench on the nuts on the bottom side of the manifolds.

This problem also has two possible solutions: A) move the engine on its mounts again; or B) unscrew the studs so the manifold can come out vertically without having to clear the studs. Of course, unscrewing the nuts is hard enough, unscrewing the studs is likely to be seriously difficult. Here's an idea: remove all the nuts first, then back the manifold up against the chassis so you have a gap between the manifold and the head. Using a thin pair of pliers, reach between the gap and unscrew the top three studs and then the bottom three studs. This method has the advantage that you will be gripping the studs near the middle and therefore not boogering up the threads where they're actually used. Note that two of the studs on the bottom of each rear exhaust manifold cannot come out through the manifold; they will either have to be removed with the manifold or the manifold will have to be repositioned -- perhaps downward, perhaps tilted -- to get those studs out. All the while, keep in mind that you will have to put this manifold back on somehow.

Actually, leaving the manifolds on the heads and moving the engine has its benefits. For one thing, you can leave the starter alone, there's no reason to mess with it. This author got his heads off by unbolting the motor mount on one side, putting a jack under the front of the engine and jacking, causing the engine to rise and tilt. After one head came off, the engine was lowered, the mount reconnected, the other mount unbolted, and the engine jacked back up so it tilted the other way to remove the other head.

David Johnson says, "It was easier for me to remove both motor mounts and lower engine to get enough clearance." Johnson goes on to say that, even though he pulled the heads with the manifolds still attached, he went the other way on reassembly. "I did that because I couldn't get 2 nuts off the bottom because some &^%%$ had galled up the threads and the nut wouldn't come off, and the stud was trapped. Now that I replaced the studs with new, and with the ever present anti-seize it was much easier to put it on after."

Whatever method is used to deal with the exhaust manifolds, make sure to take enough notes to be able to reinstall the heads and reassemble the car.

One other thing to note: you may find it helpful to remove the rear pair of cam bearing cap studs to ease clearing things getting the head in and out of the engine compartment.

STUCK HEADS: When you actually get to pulling the head off, if it's never been off before you'll probably find it stuck. In general, being stuck means one of two things: the head and block are glued together at the gasket, or the studs are stuck in the holes. The difference becomes evident when you actually get it loose: if it was stuck at the gasket, then once it's broken loose it slides easily off the rest of the way off the studs. This is typically not the case with the V12 heads, which have metal-faced gaskets that don't stick much, but the crud really builds up around the studs (several of which are immersed in coolant) and makes it difficult to get the head off every bit of the way. You might get it an inch up and still be having difficulty moving it.

This author will express an opinion here: the stuff plugging the openings around the studs is very likely the Barr's Leaks that Jaguar recommends putting in the coolant. Heads that have been off before and never exposed to Barr's Leaks again typically come right off without any more effort than lifting by hand. Of course, rust particles or other deposits in the coolant might also contribute to the jamming, but careful maintenance of the coolant seems to avoid those problems.

Loren Lingren sends this tip: "The stuck head syndrome seems to be caused by corrosion between the head studs (usually only the long ones) and the head. With all the nuts removed, try to wiggle the end of each stud by hand. The stuck ones will not move. Begin soaking each stud with a good penetrating oil. Get several 7/16 SAE nuts (Don't use the head nuts unless you have extras) and an air hammer with a tie rod tool attachment. The idea is to vibrate the studs with the air hammer, protecting the threads with the disposable nuts. Caution must be used not to bend the studs or gouge the head surface. Continue to apply penetrant as work is done. As the studs loosen, the penetrant will disappear down between the head and stud. I have used this procedure successfully for several years in removing even the most stubborn heads, 6 or 12 cyl, without any expensive side effects."

Other substances suggested for loosening the crud in the stud holes include oven cleaner, alloy wheel cleaner, phosphoric acid, Nitromors, and Coca Cola. Dr. Karsten Eller, chemist, says to forget about the oven cleaner: "Oven cleaner is mainly caustic soda, i. e. NaOH. The sodium hydroxide attacks the protective alumina coating on the aluminium and also dissolves aluminium metal:

2 Al + 2 NaOH + 6 H2O = 2 Na[Al(OH)4] + 3 H2

"Use of oven cleaner is therefore strongly dissuaded from."

Eller says acid will be fine, however. Mike Morrin says, "Someone suggested using phosphoric acid (rust killer) as it dissolves the rust without damaging the aluminium. He also suggested moulding little dams in plasticine to hold the stuff around the studs."

Regarding the use of Coke, Craig Sawyers says, "Now here's an interesting connection. Coke contains phosphoric acid (that is why it rots your teeth)."

John Warr says, "Nitromors is not actually acidic - It contains dichloromethane, which will remove most hydrocarbon based gunge. It plays havoc with the skin however, and the vapour will go across most types of glove.

"I think alloy wheel cleaner will do the trick quite well."

Of course, another fine idea would be to unscrew the studs and take them out. Probably not even worth trying, though; you can't get very good access to the studs with the head in place, and they are likely to be trouble to remove -- see the section on replacing head studs below.

Malcolm Scott suggests, "I bolted on to the exhaust studs a heavy metal plate that had sufficient rise in it so that I could use a hammer. This separated the head from the block and loosened the head from all studs along the exhaust side. However, two studs near the rear under the inlets were clearly holding things up. On the HE heads, the inlet tract protrudes over the smaller studs. I put the nuts back on the two offending studs and put solid packing between the nut and the bottom of the inlet. I then carefully wound the nuts off and the heads pushed off easily. Because the studs had grown into the head, they would not let go until the head was about 0.5 inch off. This required loosening of the nuts and adding solid packing (I used other nuts and washers)."

Richard Chapman suggests that you remove the cam so that all the valves are closed, then feed rope into the spark plug holes on cylinders 1 and 6. Turn the crank over and let the pistons push the head off. Might also work on cylinders 2 and 5.

John Napoli: "There is a technique that we used successfully on much lesser cars. The trick is that you need to try this before you dissasemble very much. The trick is to loosen as many head nuts as you can access, and then run the engine!! One good stab of the throttle is usually all it takes. The head quickly 'pops' a bit. Shut it down and then remove the heads normally. You only need to loosen the nuts a couple of turns, and it often doesn't

matter if you can't get to 'em all. We used to do this on engines where, for whatever reason, we anticipated problems in getting the heads off."

If nothing else works, John Goodman describes a homemade tool that will get the heads off: "1/2" steel plate slightly wider and longer than the cyl head. Drill two rows of holes down the centre to line up with the camshaft bearing cap mounting holes, bolt plate onto camshaft carrier using the existing bearing cap studs. Screw long bolts through threaded holes in the outside edges of this plate which line up with the cyl head retaining studs, the ends of these long bolts had "cups" to locate them over the cyl head studs. Next just torque down evenly with a few smacks from a BRO hammer and the heads come off." If you have the tappet block off, you might be able to use it as a template to mark where to drill holes in the plate.

Alternatively, a smaller, more compact set of tools that work essentially the same way as Goodman's massive plate can be fabbed up quite easily. First, purchase a length of steel bar 1/2" thick and 1" or 1-1/2" wide and cut two pieces 4-1/2" long from it. Drill two holes and drill and tap two other holes in each piece as shown in Figure 4. Into those tapped holes, thread 3/8"-16 bolts that are at least 5 inches long and threaded all the way to the head. 

If you want, you can use 3/8" fine thread bolts and tap the plate accordingly, or even 8mm metric stuff -- whatever is easiest to find in your area. You can use threaded rod, but you'll need to find a way to turn the threaded rod -- weld a nut onto it, bend it 90† at one end, whatever. If you don't have a tap or don't want to bother, you can just drill 3/8" holes and put nuts on the back side of the plate, but it'll make the tool a little clumsier to use.

The tappet block should be in place, and you'll need to remove the bearing caps and the camshaft. If you've already removed the tappet block, just slide it back on; without the tappet block, it's too easy to bend the studs using this tool. There are seven pairs of studs for cam bearing caps on each bank; this tool can be used on the 2nd, 3rd, 5th, or 6th pair. Fit these two plates to the 2nd and 6th pairs and put nuts on to hold them in place. You might need to put some spacers under the nuts on the studs -- 3/8" nuts work fine.

To begin with, install some generic nuts on the top of each of the four head studs that will be involved, threading them on only a couple turns. When the jacking screws are inserted into the center of these nuts, the nuts will keep the screws from walking off the end of the stud. However, when the head has been lifted to the point where these nuts keep it from coming any further off, you'll have to stop everything and remove the nuts. Things may be moving well enough by that point to continue without anything to hold the jacking screws centered, but if not a few small pieces of 7/16" ID tubing slid over the studs will help -- or maybe some 1/2" nuts. Once the jacking screws enter the holes in the head, there is no further need for such things, the head itself will hold the jacking screws aligned.

It may be possible to get a mildly stuck head loose with only one tool by fitting it to the 2nd pair of studs, getting that end loose, then relocating it to the 6th pair and getting that end loose. But since the trouble is likely to be from junk packed around the studs and will be trouble all the way up, it'll be a lot easier to make two of these tools and jack both ends simultaneously.

When jacking, take care not to allow the head to tilt inward or outward; tighten both jacking screws on each tool evenly. If the head cocks, it just jams worse on the studs.

Note that the weak point on these contraptions is probably the cam bearing studs themselves. Don't go cranking real hard; if the head just won't come loose, find a way to apply more lift elsewhere -- don't just pull the studs out of the top of the head. Since they're only attached to two studs each, these little tools won't apply the lifting force that Goodman's massive plate will, but it should get most heads off. If more force is required, two more plates could be fabbed and installed on the 3rd and 5th pairs of studs to apply more oomph. You could even fab a fifth plate with no 1/8" offset between the pairs of holes to use on the 4th (center) set of studs.

Matthias Fouquet-Lapar quotes the "XJ-S issue" (Volume 8 Number 3 January/February 1996) of Jaguar World, page 57 :

Cylinder heads can be a nightmare to lift due to the inter-action of steel studs and alloy heads. However, Classic Spares do market a tool of their own design that makes light work of the job. Be warned, you will need it.

There are also reports that John's Cars offers such a tool.

Finally, note that if you purchase a "head set" -- a set of gaskets intended to include everything you need when you take the heads off -- the set will not include the locking plates for the cam sprocket bolts, C33917. You will need four new ones, so make sure to order them at the same time.

SO YOU HAVE THE HEAD OFF: Be sure and clean up the spark plug threads while you have the head off. One excellent method is to get a suitable wire brush shaped like a "bottle brush" and "screw" the brush through the hole. When clean, the spark plugs should spin all the way down by hand. You might also want to address any spark plug threads that may be damaged; it's easier to install an insert now than later on when the engine is together.

If the block hasn't been turned upside down in the midst of this job (!), there will be little puddles of coolant surrounding the liners. Make sure you get this coolant out, and then scrape the bottom of these pockets with something pointy. You'll probably find a lot of junk, perhaps looking like sand. It might actually be sand left over from the casting process. David Johnson says, "I discovered that there was no coolant flow around the last cylinder on my A side! The last liner is so close to the jacket that yuck had built up to the point that coolant would have had a hell of a time trying to flow around it. I'd bet only about 1/2 the liner had coolant touching it!" Whatever you find, get it outta there. Small accumulations probably don't hurt anything being there, but these pockets may serve a useful purpose in catching new crud floating around in the cooling circuit, and maybe once they're full stuff starts plugging the radiator or something.

On the bottom of the heads where they come in contact with the gasket, there are several openings for coolant to flow from the block through holes in the gasket and into the head. One row is round openings, the other row is oblong holes. Several of these holes may be rimmed with casting flashing; apparently the core meets the form right at the hole, and there was little effort to clean away the flashing at the factory. When the head is off, take a Dremel and clear away this flashing to ensure the holes are fully open. Might not be a big deal, but couldn't hurt.

With the Jaguar V12, you might be surprised at just how much you can accomplish with the heads off without opening the bottom end. The first possibility of note is that you can seal the liners to the block. Use the liner retainers (or some reasonable facsimiles) to hold 11 liners in place. Turn the crank until the piston in the one unrestrained cylinder is at the bottom of its stroke, and then continue turning the crank while encouraging the liner to come up with the piston. When the piston is at TDC but still at the bottom of the liner, the ledge on the side of the liner that sits on the block will be higher than the head surface. You can then carefully clean the surface on the liner and the block, apply new sealant, and slide the liner back into place. David Johnson actually used this method to reseal a liner that had accidentally come loose, and ended up knocking a few more loose just to make sure they were all properly sealed. In fact, it might not be a bad idea to turn the crank a little with no retainers in place, just to see if any liners are loose enough to move. Or, succumb to the temptation to reseal them all whether they need it or not.

Now we move on into theoretical, since as of this writing the following ideas have not been tried and reported back on; attempt at your own risk. The next suggestion is that you may be able to replace the liners from above. This is a bit harder than the resealing idea, since it requires taking each liner completely out. The challenge is getting the piston rings back into the liners when reassembling, since even with the piston at TDC you're working in too tight a place to use a ring compressor. However, the bottom end of the liner seems to have a bit of a chamfer on it, so you may actually be able to finger the rings into place one at a time. Squeeze the top ring, slide the liner down on it, and move on to the second ring. Or, you might be able to fashion a ring compressor that will work in this space, perhaps from a hose clamp.

If that idea works, the next idea should work too: replacing the piston rings. If you have the liner out and the piston is flopping around above the opening in the block, it shouldn't be too difficult to carefully remove the old rings and slip on some new ones.

One last idea: replacing the pistons themselves. If you pull two adjacent liners at the same time and rotate the crank until one piston is high and the other is low, perhaps the C-clips can be removed and the pin slid out over top of the adjacent piston.

CLEANING HEAD STUD HOLES: Before reinstalling the head, it is of utmost importance that the holes for the studs be thoroughly cleaned. Any crud remaining in these holes may be kicked loose when the head is slid down over the studs and it might fall out the bottom and sit on top of the head gasket while you're closing it up, and you'll have a bad seal.

For cleaning the stud holes, a suitable item would be a wire brush shaped like a "bottle brush". If you're real lucky, you might find one in an auto parts store, and if you're even luckier it might be somewhere near the correct size. Forget about luck, and visit any sporting goods store or department and look at the tools available for cleaning rifle and shotgun barrels. Outers and Hoppe's make 3-piece rods and little brushes that screw onto the end for very reasonable prices. Buy one shotgun-cleaning rod assembly and then select brass wire brushes for 10, 12, 16, 20, 28, and .410 gauge shotguns, and you'll be able to clean just about any size hole you encounter. You can opt for the rifle and pistol cleaning tools as well for cleaning smaller holes yet, but note that the threads on the brush itself might be different and therefore require either a different rod or an adapter.

As opposed to the items found in an auto parts store with handles that are merely a continuation of the twisted wires that form the brush itself, the shotgun rod assembly is a finely machined aluminum rod. Hence, it becomes quite reasonable to chuck one section of the rod up in the variable-speed drill and clean those stud holes up in a hurry!

REPLACING HEAD STUDS: Some of the head studs on the V12 are immersed in coolant. If the coolant has not been maintained properly (changed on schedule), some of these studs may get corroded. A small amount of surface corrosion is no big deal, but large-scale erosion can signficantly reduce the cross-sectional area of the stud -- which is a formula for blown head gaskets.

Head studs can be thought of as springs. When you tighten the nuts to the specified torque, you are stretching these springs to a particular load value. Even though parts may expand a little with changes in temperature, the studs are designed to be long enough that this growth is minor compared to the stretch of the studs so the compressive force on the head is constant. But if the sides of the studs start corroding away, this preload is reduced. And if the engine is reassembled without replacing such corroded studs, it may prove impossible to apply the specified torque; the bolt may yield at the narrowed section first.

Peter Hyslop shares experience with these studs: "This applies mainly to old V12 engines (ie >20 years old) with a few miles on them and which have never been apart:

1) The studs can get stretched if over-torqued by some fool trying to take a short-cut on a head gasket leak ... this is an unusual degree of incompetence, so never use that mechanic again (and if you did it yourself, give up, there's no hope for you).

2) The studs immersed in the coolant can corrode and pit. The others are usually fine.

3) The studs immersed in the coolant can become adherent to the block and become brittle. Some of these studs stand a reasonable chance of snapping off when you try to remove them ... yes, you read it correctly, the stud will snap before the aluminium block gives way.

The solution:

• Make sure that you really want to go this far before you start, and are prepared to stick it out when the going gets tough... get a consultation with someone who knows what they are doing and can haul your arse out of the fire (in my case Lou Fidanza at GTJ and Clive Freeman at British Autosport).
• Leave the studs not in the coolant alone.
• Pull the studs in coolant only if corroded.
• Expect some of the corroded bolts to snap and land you with a big machinists' bill.
• Replace the studs with something modern like GTJ's moly steel ones.

How do I know?...I'm up to my arse in the alligators right now with items two and three above (yup, snap, snap snap)!"

Note that the 6-cylinder engine used in some XJ-S's has an entirely different theory in head studs. They are designed to be tightened until they yield, which provides a very closely controlled amount of compression on the head gasket -- but requires that the studs be replaced whenever the head is pulled.

FIDDLING WITH THE TIMING CHAIN: If, for some reason, your timing chain isn't sitting on the sprocket on the holding bracket when you put the head on, David Johnson says, "if you have already installed cam, be sure that you take the moment and hook the cam chain over the bracket meant to hang sprocket on. I looked at it and told myself, "Why bother? I can simply reach down there and pull it up." Ain't so. The flange and bracket are just this much too close to squeeze the chain through."

CYLINDER HEAD NUTS/WASHERS: The thick washers under the 7/16" nuts are quite suitable for the job, and the thin washers under the 3/8" nuts under the intake ports seem to work well enough. The same thin washers used under the 3/8" nuts along the exhaust manifold edge of the head don't seem to be cutting the mustard, though. They are likely to be "dished" when removed where the nut is depressing them down into the soft aluminum of the head. To improve this situation, one of three tactics is recommended: replace the washers with thicker washers; replace the nuts with washer-face nuts that will contact the original washer across most of its surface; or -- as a minimum fix -- install two washers under each nut. CarQuest auto parts (and undoubtedly some other better auto parts shops, but notably not some of the discount or bargain auto parts stores) offers a Dorman "manifold stud washer" number 685-050 which is quite suitable for this task. Note that these washers are not found on a bubble card on a rack, but rather in a case of heavy red and black metal drawers that form the Dorman display -- often found behind the counter. Look in the drawer labelled "manifold studs". This washer is about 1/8" thick (like the washers under the 7/16" nuts), fits very snugly around the 3/8" stud, and has a somewhat larger OD than the flimsy original washer.

The nuts holding the heads to the block, as in other engines, require careful torquing in progression to ensure proper sealing of the head gasket. However, there are head nuts on the Jaguar V12 that are tucked underneath ledges, making it difficult or impossible to get a socket in place. This application requires a tool called a crowfoot wrench. This tool looks like a sawed-off open end wrench with a square drive hole for attachment of a ratchet and extension. Since they are useful tools anyway and come in handy on other hard-to-reach places, it is recommended an entire SAE set be purchased. David Johnson suggests that, if you can find a set, buy closed-end crowfoot wrenches, since the torque applied to the 3/8" head nuts threatens to spread the 9/16" open end crowfoot and round the corners of the nut.

When using crowfoot wrenches in conjunction with a torque wrench, the crowfoot should always be attached to form a 90ƒ angle with the handle of the torque wrench. The effective lever length of the torque wrench (distance from the handle to the centerline of the bolt or nut being torqued) is not changed. If the crowfoot is attached in line with the handle, the lever length is altered, and the torque readings will be inaccurate.

The purpose of torquing head nuts to a specified value is to obtain a certain amount of tension on the studs themselves. Whether or not the threads on the nuts are lubricated makes a huge difference in how much tension results from a given torque, as does whether or not the contact between the nut and the steel washer it sits on is lubricated. Unfortunately, the manuals are not as clear as they might be on whether or not the specified torque is intended to mean with or without lubrication. In its section on General Fitting Instructions, the Jaguar Repair Operation Manual does say "Always oil thread lightly before tightening to ensure a free running thread, except in the case of self-locking nuts." This makes sense, since tension obtained from lubricated threads is more consistent than from non-lubricated threads; if the threads aren't lubricated, there's no telling how much tension you'll end up with. There seems to be little or no official guidance for lubricating the washer face, though.

This author recommends you lubricate the head stud threads with anti-seize compound; this may not sound like oiling lightly, but the amount of friction in the threads when installing should be comparable. Plus, the anti-seize compound will ensure the threads are not damaged when removing the nuts next time.

This author also recommends you apply Hylomar or comparable non-hardening sealant (or Loctite 573 -- see notes on sealing the tappet block) to the contact areas between the washer and the head and between the nut and the washer on the 7/16" nuts only. On ten of the fourteen 7/16" studs per head, these contacts seal the coolant circuit; that's why these nuts are cap nuts, since coolant can't leak through the threads on a cap nut (and you thought Jaguar used cap nuts to make it pretty!). While not intended as a lubricant, the sealant will provide a fairly consistent amount of friction between the nut and the washer, and therefore a consistent application of tension to the stud.

On the 3/8 studs, apply anti-seize compound between the washer and the nut. You can leave the contact surface between the washer and the head dry, apply sealant, apply anti-seize compound, whatever, it shouldn't make any difference.

Needless to say, if any of the threads on studs or nuts are boogered up enough that the nut won't spin on freely, they must be cleaned up or replaced before torquing.

When torquing down the nuts, aim for the low end of the spec range, and be alert for signs of stud yielding: the nut continues to turn without the torque increasing any more. If the specified torque is attained in a smooth and progressive manner, there is nothing else to worry about; the head is on and secure, and there is fully adequate tension on the studs to make sure the head gasket will remain sealed. On the other hand, if either the threads or the washer face is assembled dry, you won't know how much of your tightening torque was lost there, so you won't know just how much tension actually got applied to the stud -- and therefore you won't know how long your head gasket is going to last.

SEALING THE DIPSTICK TUBE: The dipstick tube just slides into a tube on the crankcase and is held in place by a bracket bolted to the top of the head. It's not sealed. Of course, it'd be a nice idea to seal it; the fewer leaks, the better, and even if the dipstick itself doesn't seal perfectly (although it just might -- it is a decent design) it'd be a lot harder for oil to find its way all the way to the top of the tube than to leak out right there at the bottom.

Some ideas for sealing this thing: You might apply a sealant to the end of the tube before sliding it back in. Loctite 573 might be a good choice (see the section on sealing the tappet block). Or, you might fit a small O-ring around the tube before installing it, and make sure that the bracket arrangement holds the tube firmly so it applies a little compression onto the end of the fitting on the crankcase. Of course, Viton is preferred. Or, if you can get your hands in there, you could slide a piece of fuel hose over the joint and clamp it on both sides of the joint.

FREEZE PLUGS: Apparently a US-only misnomer; English-speaking countries reportedly properly call them "core plugs." Some US parts places call them "expansion plugs". Alex Dorne clarifies, "I can tell you that the freeze plugs are not meant to rescue the block if the coolant freezes. Due to the casting process they were necessary to make mantling of the block possible." Of course, that doesn't mean they won't pop out when the coolant freezes! However, in warmer climates the most common failure is rust-through.

If you need to replace these plugs for whatever reason, you will find several versions available, including simple steel or brass cup-shaped plugs, and copper or rubber assemblies with a bolt through the center for compressing the plug to expand it into the opening. Dorne: "Most common material seems to be steel for automotive use but when working in the marine business I found out that copper is used on "factory built" marine engines to prevent corrosion problems when fresh water cooled.

Note that the original plugs are concave side out, but replacements are installed the other way. "Installing the plugs is a piece of cake (if the block is out of the vehicle, of course). Place the plug in its seat, convex side out, hold a ball ended hammer in the center of the plug, give it a hit with a second hammer. This flattens the plug and increases the diameter a little bit. I think it's a good idea to use some non-hardening sealant on the seat before placing the plug."

If the cupped plug is a little too tight to install, it is a simple matter to make it a little smaller. Set the plug in a large socket or box end wrench, put a steel ball (or the head of a ballpien hammer) in the center and hit it with a hammer.

Since the Jaguar V12 has an open-top deck design, there is little reason for other casting openings and there are no plugs on the side of the block. There is one plug on the rear end of each bank, within the bellhousing. On the head, there are three 7/8" plugs on the exhaust side, four 7/8" plugs on the intake side (visible within the V), and one 1-3/8" plug at the back end.

VALVE REMOVAL: Jan Wikström says, "The normal generic valve compressor from K-mart will do fine; there's nothing special about the V12 valves."

Apparently, K-mart is a quality tool source in Australia. Here in the US, the vast majority of valve spring compressors on the market are either cheap junk, designed specifically to fit a Chevy and nothing else, or both. Trying to use cheap junk on valve springs can be seriously dangerous; if that thing snaps loose or breaks while holding the springs fully compressed, it can fire keepers and collars around the room like bullets.

Some of these pieces of junk are intended to be operated from above only, which may be handy if you are trying to replace seals without pulling the heads, but these tools try to hook onto the coils directly; they compress part of the spring rather than the whole length of the spring, and they don't compress the inner spring at all -- you have to push down on the tool to get the keepers in and out. And you must hold the valve itself in place by other means, possibly applying compressed air to a spark plug hole or even inserting some rope and turning the engine around until the piston pushes it against the valve head.

If you have the head off, Gerald Foster recommends a valve spring compressor sold by Sears. It costs less than $20, is a substantial tool that wraps around the head (like a big C-clamp) to push on the spring and the valve head at the same time, and is a Craftsman tool with a lifetime warranty.

When using the C-clamp type compressor, you'll find it helpful to tighten down on the spring a little bit and then give the top of the spring a little rap with a plastic hammer to pop the collar loose from the keepers. Then you can proceed to compress the spring further.

VALVE TRIMMING: After the valves and seats have been machined to renew the contact surfaces, the valve will obviously sit lower in the head. This closes up the valve clearances at the tappets. Jim Cantrell points out: "Often, people at this point will then cut the valve stem to get the additional clearance. This will then cause the valve stem's life to be reduced since the stems are hardened. This hardening only penetrates a few thousandths of an inch and cutting it off exposes the softer valve material." The proper solution to inadequate clearance is to replace the valve, the seat, or both.

OIL PRESSURE: An oil-fed sleeve bearing, such as used in the main and connecting rod bearings of automobile engines, is an excellent device -- much more so than most people understand. When the parts are rotating, the parts ride up on a film of oil, much like skimboarders skim easily across very shallow water and seem to coast forever. When operating properly, the metal parts do not touch each other, and there is essentially zero wear. The friction is entirely within the film of oil.

This system doesn't work at a standstill, however, the same way the skimboarder will sink to the bottom when he stops moving. The entire reason engine bearings have a soft, replaceable surface is because they must ride on this surface for a very brief time at startup, before oil is pumped to the bearings and before the bearings establish a film to ride on. The hard steel surface of the crankshaft should slide on the soft bearing with very little wear on either, but startups still account for the vast majority of normal bearing wear.

The shearing action of the oil tends to heat it somewhat; there is very little heat generated from shear, however, and many cars get by without oil coolers. The main cause of heating of the oil is by contact with hot parts, notably the bottom surface of the pistons.

The pistons are likewise supposed to skim up and down the cylinders on a similar film of oil. It doesn't work nearly as well, though, since the piston stops at each end of its travel for an instant, and because there is a less positive flow of oil to this area.

This system also does not work very well for the contact between the camshaft and the followers. This is because the contact area is a very thin line rather than a broad area. If one of the two parts were as soft as the crankshaft bearings are, the force at the contact point would quickly tear it up. In the Jaguar V12, these parts are immersed in oil during operation. This ensures they are adequately lubricated, even during startup since the oil stays there, but it also generates more heat churning the oil.

There are two primary bearing failure modes in any engine that result from lubrication problems. The first and most easily understood is excessive wear and damage due to lack of lubrication. The second is bearing overheating due to insufficient cooling oil flow. These two are very different; in the latter case, the bearing may have enough lubrication to prevent wear, but gets hot enough to melt the soft bearing material because the same oil is staying in there and getting hotter and hotter, rather than cool oil flowing through.

All engines tend to display a drop in oil pressure at idle; the pump moves less oil when the engine is turning slower, but the openings through which the oil flows are the same size no matter what the engine speed. The Jaguar V12 is no exception, and sometimes shows lower oil pressure when hot and idling, especially when it has a few miles on it. The V12, when running on all cylinders, can idle very slowly, causing even lower pressure. This causes many XJ-S owners to panic, and some to take poorly conceived countermeasures.

There is no magic value for oil pressure. The only real need for any pressure at all is to get oil to all points in the engine, and this would only require a couple psi. Oil pressure is monitored simply to insure there is oil flow, which is essential.

If your car has always had low pressure at idle when hot, and it gradually over the years gets a little lower, don't worry about it. If it suddenly has much lower pressure than it used to, you may have a damaged bearing that is allowing oil to flow through too fast; the cause should be investigated. If your car suddenly has no oil pressure at all, stop immediately, do not drive it one more minute until the problem is located and corrected. Many motorists fail to understand the importance of this, so I will emphasize: if the red light on the dash comes on indicating that you have no oil pressure, it is not good enough to "take the next exit." You should pull over immediately, possibly even shutting the engine off while still moving. A towing fee, and even an illegal parking ticket, is a minor expense compared with an engine replacement, which is the inevitable result of driving with no oil pressure.

Do not add oil thickeners to your oil. While these may increase the indicated oil pressure at idle when hot, they do no real good, and can do considerable harm. In particular, when cold the oil may be so thick that very little flows and most of the output of the oil pump is wastegated through the pressure relief valve. While there is good pressure, there is little flow to the bearings, and they may fail due to lack of cooling flow before the engine and the oil warm up. This is also a good reason not to run the engine too hard until it is fully warmed up.

OIL CHANGING: If you buy an oil drain pan from the local auto parts store, slide it under the Jag, and open the plug in the sump, you may be in for a messy surprise. The Jag V12 will drain around 11 US quarts of oil, and this is more than the capacity of most conventional oil drain pans. Either be sure to get a really big pan, or figure out how to drain the sump into two pans.

When changing the oil on the XJ-S, it may be worth noting that the oil cooler at the front of the car has drain plugs on both ends, and openings in the bodywork to get to them. If the oil is drained from the cooler as well as from the sump, perhaps more crud will be removed from the engine.

OIL FILTER REPLACEMENT: The oil filter on the Jaguar XJ-S mounts nearly vertically, the way they all should be; the dirt stays in the filter as it's being removed. Considering the position, you can do your engine a favor by filling the new filter with oil prior to installing it. When you start up, you will get pressure that much sooner. You will find it helpful to use a small screwdriver or some such to poke through the smaller holes in the base of the filter and push open the flap a little to provide a vent while trying to pour oil in the center hole.

It has been noticed that some filters for the XJ-S are different from others. Some are very large, extending almost level with the bottom of the pan. Others are of conventional size. Some have a series of flats around the bottom edge to fit the socket-type filter wrench that goes on the end, and some don't. Since you can't get to this filter from the side, it is recommended you get a filter wrench that can be used from the end, and make sure the filters you purchase can be removed with your wrench. The socket-type filter wrench works well and is cheap, but requires the series of flats on the filter. There are also coil type and strap type filter wrenches that will work on most any filter; note that the coil type cannot be used to tighten the filter.

OIL FILTER REPLACEMENT -- EARLY CANISTER TYPE: Until sometime in 1976, the XJ-S came with a canister filter assembly. Not only does this make it more difficult to change, but more care must be taken to make sure everything is working properly. Mike Morrin says, "The cartridge filter has a bypass valve which sits inside the bottom of the cartridge, and seems to be there to bypass the filter when it gets clogged. When I had the old cartridge out and was cleaning the parts (such as the bypass valve) which get re-used, I noticed that the bypass valve was actually about half way open!! This is presumably not good for filtration efficiency. On dismanting the bypass valve, it became apparent that the alloy valve body had been strained, probably by someone tightening up the filter assembly with something not seated correctly. I was able to straighten and reassemble the valve, and it looks like it should work as good as new."

OIL CONTAMINATION: Much of the following was pilfered from an article by Nigel Calder in the March/April 1994 issue of Ocean Navigator magazine. It was primarily about auxiliary engines for sailboats, but the issues discussed here apply to any piston engine.

Oil contamination is divided into two categories: chemical and physical contamination.

Chemical contamination degrades the oil, causing a loss of lubricating properties, and also may introduce substances that attack engine parts. Heat and age can cause oil to oxidize and thicken, encouraging the formation of sludges and varnish. Water can be introduced even in a tight engine by condensation within the crankcase, and causes emulsification. If there happens to be any sulfur in the fuel, some can find its way past the rings and combine with water to form sulfuric acid which promptly attacks engine parts. Unburned fuel coming past the rings also dilutes the oil, lowering its viscosity.

Chemical contamination is combated by additives in the oil. Eventually, however, the additives are consumed and fail to counteract the contaminants. At this point, the oil needs to be changed.

Physical contamination refers to metal particles and dirt in the oil. The metal particles come from wear between moving parts. The dirt comes through the intakes, and a portion makes it past the rings. The problem is obvious in that such particles will increase the wear on bearings and the like.

It is tempting to take comfort that the oil filter is preventing the particles from getting into the workings of the engine. Unfortunately, it is not as effective as one could hope. The typical paper-element oil filter will catch particles down to about 30 or 40 microns, but damage is caused by particles down to about 2.5 microns. These smaller particles build up in the oil and pass right through the filter, cycling through the engine again and again.

The full-flow filter cannot be made with a tighter mesh because the restriction to oil flow would be too great. In addition, if the filter gets clogged, either the element breaks open (dumping all the dirt into the engine), or the flow is inhibited. Usually a relief valve is provided to allow oil to bypass a clogged filter, allowing crud of all sizes to circulate through the engine.

There are two excellent ways to combat physical contamination. The first is by installing a bypass filter. A small percentage of the pressurized oil from the outlet of the full-flow filter is diverted into a separate filter with a tight mesh element to stop particles down to 2.5 microns, and from there right back into the sump. An orifice is provided to prevent an excessive amount of oil from taking this route, which might starve the engine. If the filter gets plugged, no problem -- the flow stops, and 100% of the oil goes through the galley as before. But as long as a small amount is going through the bypass filter, within only a few minutes all of the engine oil is cycled through it and the amount of suspended particles is greatly reduced.

The other method is essentially the same, except that the bypass filter is replaced by a centrifuge that causes the particles to collect on the inside of a spinning cylinder. These are typically only available for larger engines.

These solutions are even better than changing oil at short intervals. Even with frequent oil changes, particles appear in the oil immediately and continue to build up. The bypass filter, however, continuously keeps such particles from causing engine wear.

Note that a bypass filter does not address chemical contamination. Such an installation would be effective at reducing engine wear, but the oil needs to be changed at the same intervals to prevent the additives from failing.

An outfit called TF Purifiner offers a package that includes a bypass filter system along with a small heater that boils off water, fuel, and coolant to minimize the chemical contamination so the additives last longer.

Surfing the WWW, Mike Claus found that other products are available from Baker Precision Bearing, Fram and Amsoil. "Fram offers an automotive by-pass filter in its product line that features a pleated-paper element and easy "spin-on" replacement similar to original-equipment-type units. Ask for the Fram "PB50" with mounting hardware.

"Amsoil's bypass unit is connected to the oil pressure sending unit and returns oil to the pan, thus requiring some mechanical ability or the services of your mechanic for the initial installation. The company states that its bypass unit, which employs a user replaceable, pressed-fiber element, refilters all the oil in an engine every five minutes, and keeps it analytically sparkling clean for the (recommended maximum) element life of 25,000 miles! It even extracts and contains any water that has (inevitably) condensed into the oil...which if allowed to remain in circulation will often result in the formation of corrosive acids."

Of course, one might immediately ask: if a bypass filter is such a good idea, why didn't such a quality automobile as a Jaguar come with one from the factory? Well, you have to consider the options the way the manufacturer does. The lack of a bypass filter will not cause engine failure before some extended mileage, especially if the owner has been paying the dealer for oil changes on a regular basis -- and even if the engine does fail due to dirty oil, the manufacturer is not likely to incur any liability. The additional cost, multiplying the cost per car times the thousands of cars sold, is significant. And the additional risk of failure -- one of the oil lines to a bypass filter blowing open or some such -- may be more than the company wants to accept. Just having to tell prospective buyers that there are two oil filters that need regular changing may be seen as a marketing disaster, especially in this era of drive-it-and-forget-it cars.

You, as the owner of the car, may think differently. You have a significant investment in your car, the risk of a blown high-pressure oil hose is no big deal to you (messy, but not particularly expensive), and you are the guy who will have to pay for a new engine when this one wears out. Basically, if you are the type to own a Jaguar for the life of the car, a bypass oil filtration system would be a wise investment. Of course, if you plan on selling the car soon, or plan to crash it rather than wear it out, it'd be a waste of money.

PRE-OILING BEFORE STARTUP: A lot of the wear on any engine occurs at startup, when the engine must run for a few seconds before oil pressure is established. Russ Lehman sends this tip: "I've got a "Pre-Luber" on my van because it only gets driven about once a week or so, and the pre-lube brings the oil system up to pressure by pumping oil through the engine before starting. These pumps are fairly common on marine engines for the same reasons.

"The pump is fed from a line attached to the oil pan and pumps into a tap where the oil pressure sender is attached. The pump allows oil to pass through the normal routes for normal engine operation, while not allowing oil to pass backwards through the pump (I think it's a piston pump). The motor is switched through the ignition key in the aux position (controlled by MOSFETS), and will stop when the engine ignition is switched on."

There are other systems, including a simple pressure reservoir that holds pressurized oil after shutdown. During startup, a valve is opened, pressurizing the system before the starter is engaged.

Note that such systems may be of limited benefit. While the bearings in the bottom end of the engine may experience much less wear, it is not usually worn bottom-end bearings that require an engine rebuild. More often, it's worn pistons/rings/cylinders that eventually convince an owner it's time for an overhaul, and a preoiler does little or nothing to reduce piston/ring/cylinder wear.

OIL ADDITIVES: Don't use any. The quintessential article on the subject is "Snake Oil! Is That Additive Really A Negative?" by Fred Rau, ROAD RIDER, August 1992, Pg 15. Transcripts of this article appear in literally dozens of places on the WWW, any search should find one. A couple such places include http://www.tfpurifiner.com/snakeoil.html and http://www.euro.net/TDRS/MINIWEB/oil_additives.html

For those who feel compelled to spend more money on oil than merely following the manufacturer's recommended change intervals, the following options are suggested:

1. Install a bypass filter system -- see above.

2. Change oil more often. In fact, changing oil ridiculously often using el cheapo oil is a very workable plan, but some consider it environmentally unwise. It's also a lot of work.

3. Use synthetic oil. Tests have indicated that synthetic oil coming out after the recommended change interval is often better than new regular oil.

4. Change the filter more often. They're cheap, and indications are they get plugged and begin bypassing long before the scheduled oil change interval. 

On my car, I change the oil according to Jaguar's recommended interval (6000 miles), use synthetic oil (Mobil 1, 15W-50), and change the filter every 3000 miles.

OIL PUMP CLEARANCES: If you happen to have the Haynes manual, the clearances specified for the oil pump don't seem to make sense. So, I will include the values from the Jaguar repair manual here:

Driven gear to housing: < 0.005" (0,127mm)
Drive gear to crescent: < 0.006" (0,152mm)
End float - both gears: < 0.005" (0,127mm)

Note that, according to the manual, all measurements are taken with the pump removed from the engine. Since the crankshaft is therefore not holding the drive gear in position, it is free to move as far away from the crescent as the tightness of the gear teeth will permit. It appears a rare case that it will meet the 0.006" limit; 0.040" is more likely! Despite the clarity of their measurement procedure, it is probable that the specified values represent clearances in place, with the crank holding the drive gear in its correct location.

Mike Morrin: "I cannot believe the figures in the Jaguar manual. The endfloat on the gears in my pump was over 0.020". At the time I was rather alarmed, as the engine had by all accounts only done 55,000 miles. I carefully inspected the old parts for wear, and found that the factory machining marks were still visible on the gears, and the wear on the pump housing was negligible. This pump must have left the factory with clearances way beyond the published limits. So I put the old pump back and crossed my fingers. The oil pressure seems OK (when measured with an accurate gauge).

Of course, if endfloat is the only problem, some of us have been known to skim a little metal off the mating surface of the housing to bring it back down. With a little care, it's even possible to perform this fix on aluminum housings by laying a piece of sandpaper on a plate of glass and sliding the housing back and forth on it.

OIL PUMP REPLACEMENT: According to Thomas E. Alberts, the 1992 upgrade of the V12 included a new design oil pump -- and that the old design oil pumps are no longer available. "The original part number is C38453 or C40177. That part was officially superseded by EBC3163 which is the pump for 1992 on. EBC3163 is supposed to fit the older engines but some pieces are required to adapt it. This pump is at least twice as expensive as the earlier version, and the adapter (they call it a pump collar) is $45 plus some additional bolts are required."

ENGINE OVERHAULS: If you take your XJ-S to a disreputable dealer with major engine problems, they may tell you that a fine machine like this cannot be rebuilt, and try to charge you $10,000 to put in a new engine. Of course, one of the features that make this a fine engine is that it can be rebuilt. It is not a disposable engine; all wear items can be replaced. Even the cylinder liners can be easily replaced, so there is no need for boring and honing or for oversize pistons. Of course, if you've overheated the engine and warped the block, or you've had a major engine fire, you will definitely need a new motor.

There have been ads in Hemmings Motor News for an outfit that will replace the engine for $4,000. The job of replacing two pistons and liners cost the author less than $1,100 for parts in 1989. Any mechanic brave or knowledgeable enough to tackle the job can probably overhaul the engine for $2,000 plus his labor, depending on the damage involved.

PISTONS & CYLINDERS: In general, you can buy pistons for the V12, or you can buy cylinders with pistons. Generally, you cannot buy cylinders alone. Make very sure you don't need a cylinder before you buy a piston alone. You cannot get pistons oversized by a few thousandths for reboring cylinders; if the cylinder is worn or damaged, it must be replaced.

Fortunately, the cast iron used in the cylinders is apparently very hard and wear is usually insignificant in engines with less than 150,000 miles, in which case the pistons alone can be replaced. If rebuilding, the best policy for saving money may be as follows: don't order parts until the heads are off. Check for a "ring ridge", the step created about 1/4" from the top of the cylinder by the wear from the rings. If a ring ridge is detectable, order new cylinders with pistons. If not, order pistons alone.

The pistons and liners are available in an "A" or "B" size, which differ by a microscopic amount. The difference is a result of tolerances in manufacturing, and neither is really considered an oversize for the other. Each piston must match the liner it's installed in. There is no reason not to ensure that all cylinders within the same engine match, although differences probably wouldn't be noticeable.

The alloy piston in the V12 has a couple of steel inserts cast into the inside of the skirt. These inserts are a thermal expansion control device; they not only help control how much the piston expands when hot, they also help prevent it from ovalizing, which most pistons normally do due to the geometry of the pin bosses. When the engine goes from cold to hot, this piston design helps maintain a close tolerance between the piston and the cylinder. This, in turn, reduces ring leakage, piston/cylinder wear and noise. The fact is, these items make forged aluminum pistons look like lawn mower parts. The owner seeking to replace the pistons would be hard pressed to find better ones than the originals.

PISTON & CYLINDER CLEARANCES: According to Bob Tilley, "Under the Group C TWR build instructions for the V12, the piston to bore clearances for cylinders 1A through 5A and 1B through 5B is .0045-.005, whereas the clearance for piston to bore in cylinders 6A and 6B is .0055-.006."

These absolute values may be of little use to the normal V12 owner, since this is referring to racing engines where the pistons and the liners are likely to be significantly different than stock. The implications are fairly obvious, however: the rearmost cylinders are more likely to develop clearance problems due to poor cooling. There is no history of problems in the street application, but the information is included here for those who might make use of it. Perhaps the anal-retentive might choose to measure the clearances in their piston/liner sets and put the largest clearances at the back.

TOTAL SEAL PISTON RINGS: The use of aftermarket piston rings is a modification, and therefore is discussed in Engine Modifications. If the engine is apart for repairs anyway, this is one modification well worth consideration.

MAIN BEARING REPLACEMENT: If you find yourself needing to replace the main bearings without removing the crankshaft, the job can be accomplished the same way as most cars: Roll the upper bearing shell around and out. If it's difficult, insert a cutoff head from a nail into one of the oil passages of the crank and turn the crank to roll the bearing around. However, when installing the new bearings, remember that the Jaguar block is aluminum. It is recommended that the outer leading edge of the bearing shells be smoothed slightly with a file to prevent them digging into the aluminum when installing.

ENGINE ASSEMBLY LUBE: When an engine is first assembled is when much of the wear occurs -- in the several seconds it takes before oil pressure and flow to the bearings is established. To counter this problem, there is a product called "Penrite Camshaft & Engine Assembly Lube". This is made specifically for use on all plain bearings (mains, big ends, etc.) as well as on cams, when assembling a rebuilt engine. It claims to withstand loadings "greater than 200000 p.s.i.", which is almost 100 tons per sq. inch. It is an Australian product, but equivalents may be available in other countries.

REAR OIL SEAL: At first, it seems apparent that the upper half of the rear oil seal cannot be replaced without removing the crank. However, Dick Russ of Bethany, OK, reports that there is a tool called "Sneaky-Pete", P/N 2700 by the Lisle Company in Clarinda, IA, that will enable the seal to be replaced without removing the crank. The tool costs only $6 or so and is available at Pep Boys, AutoZone, etc. It consists of a length of music wire and some tiny grippers that can be used to bite into one end of the new seal and pull it into place around the crank.

In the December 1995 issue of British Car, Russ describes in detail how to replace this seal with the crank in place. The procedure was developed by Phil Long, and not only uses the Sneaky-Pete but also uses the seal from a 1968-78 Ford 460. The reasoning is apparently that the Ford seal is longer than the Jaguar original. After using the Sneaky-Pete to pull the new seal around the upper half of the crank, the end that has been boogered up by the grippers of the Sneaky-Pete can be simply cut off. If the Jaguar original is used, the gripper must be carefully removed and the seal backed into the recess, no easy task.

Russ also suggests that the cap be trial fit and torqued down, and then removed and inspected to make sure none of the seal is getting in between the joining faces of the cap and block and holding them apart. Any fibers or edges of the seal interfering with the fit can then simply be cut away before fitting the cap up final.

Jaguar responded in a later issue to the above procedure, claiming it was not only unacceptable but would invalidate the warranty on the engine. They insist that the only acceptable method of replacing this seal involves removing the crank so that a special Jaguar tool may be used to "size" the seal prior to assembly. The seal is not supposed to actually touch the crank at all, but to reside very close to it. The scroll carved into the crank then feeds inward, preventing oil from going outward. Contact will result in "burning", as described by many working in the area. Note that Roger Bywater seems to feel that the big problem is not burning of the seal itself, but burning of the rear main bearing; the crank rubbing on the rope seal gets the metal hot enough to damage the bearing.

Note that the original Jaguar seal is a waxy white rope, while the Ford 460 seal appears to be impregnated with graphite. Perhaps this helps avoid that burned look -- or camouflages it.

I have to add some comments here. My impression is that all of this is questionable. The scroll will do nothing when the engine isn't running -- and when it is running, the PCV system is supposed to provide a slight vacuum in the crankcase to prevent leaks. If there is no actual contact between the seal and the crank, it seems it would leak when not running -- except that the oil level is probably some considerable distance lower than this seal, so it is not immersed. Just how much do you need to overfill the sump or raise the front of the car to get a leak?

The rear journal includes a bearing followed by a slinger to throw the oil off the crank where it can drain back into the sump. Only oil that makes it past that point even gets to the seal -- perhaps explaining the burned look it gets, since it runs dry.

Perhaps any leakage doesn't involve liquid oil at all, but rather the mist of oil and fumes that exists within the crankcase during operation. If this is the case, people experiencing leaks should look at the PCV system rather than the seal; even burned, the seal should serve its apparent purpose of minimizing the air leaking in at this point so as to not overcome the PCV capacity.

Perhaps -- and this is really a stretch -- the leakage doesn't occur when the engine is running or when it's not, but only during a transition. Perhaps when shut off, some oil drips down onto the crankshaft and along it past the seal and out. Thus, only a small amount of oil would appear after shutdown, and cars stored for extended periods would not experience additional leaking from this seal. Perhaps, also, the official seal installation would work here, since a drop of oil running along the crank could be stopped by a seal in close proximity, causing the drop to lodge in the gap between the two. What would then keep the oil from going outward rather than inward, I dunno.

One more concern regarding the rear oil seal installation: when bolting up the rear bearing cap, think about how the sealing of the crankcase is accomplished. The oil seal theoretically forms a seal around the shaft, and the injection of silicone sealant effectively seals along the two sides of the bearing cap. However, the top surface of the cap is sealed only by the metal-to-metal contact. It is suggested that a thin line of sealant be applied to the top of the bearing cap, starting at the oil seal and ending at the silicone groove on each side, prior to assembly. See Figure 5. Be sure to use some type of sealant that won't obstruct the assembly of the cap to the block, such as Loctite 518.

According to Phil Bates: "In 1989, starting with engine 7P.02073, Jaguar fitted a new one-piece rear main bearing oil seal to replace the previous rope type." Unfortunately, the 7P number refers to engines for the XJ12, but Chad Bolles confirms that the XJ-S changed to the one-piece seal around the same time: "No way to retrofit, already tried that, block was recast. Crank was redesigned also. Seal is about 5 3/8's OD and 4 7/16's ID. Main bearing the same."

RUNNING WITHOUT AIR FILTER HOUSINGS: Frank Perrick points out that if the engine is to be started without the air filter housings bolted on, the bolts themselves must be screwed in. The bolts that hold the air filter back plate onto the butterfly housings actually go all the way through the housings and are threaded into the intake manifold. If these bolts are left out, the holes provide a major butterfly bypass and the engine will overrev.

AIR INJECTION PUMP: Roger Myers reports that the air pump on the XJ-S can be replaced with a GM unit. Take the old one to your local parts shop and ask them to give you one just like it.

John Napoli adds, "I have had the opportunity to see the air rails from Jag engines -- both 6 and 12 cylinder versions. Very often, the cars have brand new air pumps and diverter valves and hoses -- so someone spent a good penny replacing all that stuff. And on every one, the air rail tubes (where they stick into the head) were completely coked up. You would need some really ambitious air to get through all this!!

"Moral of the story: if you are going to maintain your air pump system, don't forget to do the obvious and simple and remove and clean out the air rail tubes. Otherwise you are just wasting time and money." Note that there's nothing complicated about those passageways, they are merely open lines into the exhaust ports. You can clear them out with a drill.

Also, please note comments in the section Engine Modifications.

AIR INJECTION PUMP WASTE OUTLET: The air pump only delivers air to the exhaust system during warmup; once the engine is warm, it wastes the air into the right side air filter housing. Michael Aiken points out that it is plumbed "to the engine side of the filter. Unfiltered air is being pumped directly into the engine - and this is very dirty air coming out of this pump! I would recommend that the wastegate tube be removed from the air cleaner housing and the opening in the housing blocked." Aiken adds that the filth coming through this line was actually visible on the inside surface of his air filter itself. He also points out that, in addition to the dust that the air injection pump may be pumping into the intakes, the pump itself is junk and may start pumping bits of itself into the intakes at any time -- rust particles, bearing bits, whatever.

It's possible that the waste line was routed to the filter housing to reduce noise, but if noise is a concern it should nevertheless be rerouted to the outside of the filter, not the inside.

AIR INJECTION NON-RETURN VALVE: Bruce Battles says that the Jaguar non-return valve "without the T-splitter is a GM part (check valve) Part # STI AV7. Just keep your T-splitter and install on the new GM check valve."

V-BELTS: Most V-belts are available in either solid or notched varieties. There is no appreciable difference in strength, since the strength of all V-belts comes from a layer of cord unaffected by notches. The cord is in the outside edge, making that part stiff to force the softer, inner portion of the belt into the groove in the pulley.

The notches in the inner surface help the V-belt flex, and are beneficial when the belt must turn around a small pulley. It is therefore recommended that a notched V-belt always be used for the alternator belt on the XJ-S.

The notches in a belt can cause noise. For this reason, most V-belts use a randomly-spaced series of notches rather than evenly-spaced, because a random spacing eliminates whine. For the same reason, cooling fans have unequally spaced blades and tires have unequally spaced tread patterns.

POWER STEERING PUMP INSTALLATION: Jim Isbell points out that the bolt holding the belt tensioner to the power steering pump should be installed from the rear to the front. "The bolt, if put in from the back with the nut end toward the radiator can be removed with the pulley in place. If put in backwards it cannot be removed with the pulley in place."

FAN BELT IDLER PULLEY INSTALLATION: Jim Isbell says: "The bolt that connects the adjuster screw to the idler pulley must be put in from the back with the nut toward the radiator. If this is put in backwards the adjustment range of the idler is greatly reduced."

IF ALL ELSE FAILS: Most Jaguar owners feel that if you want a Chevy, you should buy a Chevy. But there are those who think otherwise, and for them there are several outfits that offer kits for replacing the Jaguar V12 with a Chevy V-8. John's Cars offers two kits for the XJ-S, one for a small block Chevy and one for a big block. Another outfit to check with is Jaguars That Run.

The 90ƒ V-8 is an excellent engine layout; it has even firing order, and primary and secondary imbalances are 100% correctable by simply casting counterweights into the crankshaft. The problems with the Chevy "lump" are not that it's a V-8, or even that it's cast iron; it's problems are: A) It has pushrod-operated valves, which require severe compromises in valve operation, which prevents it from producing much power for its size -- a problem GM has always addressed by increasing its size; and B) It employs a timing chain with no tensioner, which results in an engine that runs rougher and rougher as it wears. Both of these problems were addressed and corrected by all major European automakers in the 1960's, and by all Japanese automakers in the 1970's. Both Ford and Chevy finally introduced V-8 engines with overhead cams and intelligent camshaft drive systems in the 1990's, apparently in response to competition from Lexus and Infiniti.

Sir William Lyons, founder of Jaguar, apparently didn't like V-8's. When Jaguar bought out Daimler in 1960, Daimler had two V-8 engines in production, and Lyons scrapped one of these immediately and the other a few years later. When it became apparent that the excellent Jaguar inline 6 would no longer cut the mustard on the racing circuit, Lyons responded with the V12.

If you must shoehorn a pushrod V-8 into your Jaguar, do yourself a favor and purchase some cast aluminum valve covers. They will absorb a lot of the noise of the valve train. A cast aluminum timing chain cover will also help reduce racket, and replacing the timing chain with something with less slop, like a set of gears, will make the engine run smoother.

On to the Ignition System