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 XJ-S V-12 Engine

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The Jaguar V-12, from its introduction in the E-type MkIII up to 1993, has been a 5.3 liter engine (326 c.i.) with a bore of 90 mm and a stroke of 70 mm.

Engine Design

Engines are often described by the relationship of bore to stroke. When the bore equals the stroke, the engine is described as "square." Early gasoline engines tended to have long strokes and small bores, described as "under-square." Racing engines have evolved to having the bore larger than the stroke, or "over-square." The Jaguar V-12 was designed to reestablish Jaguar's eminence as a world-beater in the racing community, and prior to the fuel crisis of the early 1970's, hence the considerably over-square design. It was quite successful in this regard, still winning LeMans races in the late 1980's.

Hot Shutdowns

It is never a good idea to shut down an engine immediately after running it hard; it is always better to run it at reduced power for a few minutes first to let it "cool down." This has nothing to do with the temperature reading of the coolant; the problem lies with parts within the engine that get much hotter at full load than at low load, and can be subjected to high thermal stresses if the transition from high load to off is too sudden.

This problem is especially serious in the case of the Jaguar XJ-S. Several problems the car seems to have, including vapor locks, distributor seizings, and ignition amplifier failures, may be exacerbated by hot shutdowns. The underhood temperatures may skyrocket after a hot shutdown, and Jaguar is known to have had underhood temperature problems during development of this car.

Whenever you are driving the car hard, always drive the car leisurely for a few minutes before shutting it off. If you are forced to shut the engine off after running hard -- having a mechanical problem, for example -- at least open the bonnet to allow the heat to rise out of the engine compartment, providing some convective cooling.

There is a relativley simple modification that can be made to the bootstrap circuit to make the electric fan cool the engine compartment better after shutoff.

H.E. vs Non-H.E. Engine

The H.E. (High Efficiency) engine, with 11.5:1 compression and a swirl combustion head designed by Porsche expert Michael May, was introduced in July 1981 and indicated by the letters "H.E." on the back of the car in place of the former "V-12" emblem. In 1986, the H.E. emblem was unceremoniously dropped and a V-12 emblem was used once again, but the car still has the H.E. engine.

If you have an engine laying around and need to know which it is, the trick is to look at the spark plugs. The plugs on the pre-H.E. are vertical, and relatively easy to replace. The plugs on the H.E. tilt toward the center just enough to make them a real pain to get a socket on. Also, the pre-H.E. plugs use a normal 13/16" spark plug socket, while the H.E. plugs have the smaller 5/8" or 16mm hex.

Engine Numbers

Richard Mansell sends this helpful data from The XJ-S Collectors Guide:

854551	February 1976	Canister type oil filter introduced
855203	October 1976	Revised EFI
856454	-	Modified fuel pump
857017	April 1077	GM400 automatic trnsmission introduced
858632	November 1977	Stronger manual transmission selector shafts
8510195	May 1978	Modified air filter box to stop blowing off!
8511262	October 1978	Ignition amplifier relocated
8513094	October 1978	Twin V groove water pump pulley introduced
8516401	November 1980	Digital-P EFI introduced
8517194	November 980	Sump plug relocated
8518001	July 1981	H.E. introduced

Most changes after this are listed by VIN number but the following are listed too:

 

8S24175	Metric threaded cylinder heads
8S26992	Piston specifications modified
8S27297	Inlet manifold modified to remove holes for cold start injectors
8S31737	Modified drive plate
8S41339	Spark plugs changed from B6EFS to BR7EFS
8S41344	Sump oil baffle plate changed
8544227	Water pump bearing size increased
8544317	Full flow oil cooling replaces relief flow
8545527	GM400 revalved, modified sump pan

Mike Morris adds:

I think that all of the engine numbers should start with 8S rather tahn 85. It might be worth adding that the numbering started with 8S1001.

V-12 5.3 vs. 6.0 Liter

Engines are often described by the relationship of bore to stroke. When the bore equals the stroke, the engine is described as "square." Early gasoline engines tended to have long strokes and small bores, described as "under-square." Racing engines have evolved to having the bore larger than the stroke, or "over-square." The Jaguar V-12 was designed to reestablish Jaguar's eminence as a world-beater in the racing community, and prior to the fuel crisis of the early 1970's, hence the considerably over-square design. It was quite successful in this regard, still winning LeMans races in the late 1980's.

The popularity of over-square engines in racing is actually somewhat artificial. Most racing programs divide competition into classes based on engine displacement. An over-square design provides the most power for a given displacement, since it permits higher rpm and provides room for large valves. However, these priorities do not translate well to street use. Over-square engines tend to be heavy for their displacement; a larger engine of comparable size and weight can be constructed with a nearly square configuration. The over-square layout also results in larger surface areas in the combustion chamber, which absorb combustion heat and reduce fuel efficiency. And while the design provides excellent power at high rpm, it tends to lack torque at lower rpm; since people like their engines to be turning slowly when cruising on the freeway, an over-square engine can seem anemic under these operating conditions.

Ford suspended production of the V-12 for 1993, and reintroduced it in 1994 as a 6.0 liter (366 c.i.). More than merely an engine enlargement, the change made the V-12 much less over-square, since the change was entirely an increase in stroke; the new engine has a 90 mm bore and a 78.5 mm stroke. This would tend to make the engine much more suitable for street use. It remains more over-square than most engines, and hence can provide excellent performance at high rpm, but is more tolerant of stop-and-go driving conditions and tall final drive ratios.

The Michael May-designed H.E. combustion chambers remain in use in the larger engine, while the compression ratio has been reduced slightly to 11.0:1.

Leaky Gaskets

Oil leaks on XJ-S's are hopefully a thing of the past. When Jaguar/Ford suspended the 12 cylinder for 1993 and reintroduced it for 1994, they updated the gaskets and seals.

The following new gaskets are "Gortex" sandwiched around metal:

Oil Filter Housing	EBC 9624
Oil Pan Gasket	EBC 9623
Cam Cover Gasket, Left	EBC 9627
Cam Cover Gasket, Right	EBC 9628

The following gaskets are two different types of material bonded together:

Valley Cover

EBC 9631

And one more, construction unknown:

Sandwich Plate Gasket

EBC 9637

These should be available at most dealers. Be sure to check the description of the gasket as some parts people will try to give you the old style to get rid of old stock.

Cam Cover Gaskets

Michael Neal, a Jaguar-certified mechanic who apparently spends a lot of his time fixing oil leaks, provides a great deal of input here. Regarding the cam cover gaskets:

New bolts are also necessary. They use an 8mm head with a built in washer. The gold finish makes them worth the price. Unfortunately these parts are only carried by the dealer.

Even using the new gaskets, Neal recommends the following procedure:

After much trial and error and the monitoring of some cars for several years I have come up with some leak-proof techniques. Only use silicone on the rear of the gaskets. Use Hylosil (British-made white silicone) to seal the end. Use a lot. Coat the half moon seal all the way around. Also coat the ends of the gaskets on both sides and one inch toward the front. Assemble and wipe off the excess silicone. Let it set up overnight! Over time, the half moon seal shrinks and the silicone retains the oil proof seal.

It's also a good idea to replace the copper seals on the cam oil feed tube.

Be sure to replace the intake manifold gaskets, even if they look OK. These gaskets can flake away, especially on reuse, and cause an intake leak that may be overlooked. This is a sure way to drop a valve seat!

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 V-12 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. I've changed over to Hylosil for this particular job. Hylosil is a white silicone type sealer with a very strong solvent. It takes longer to set up but does a much better job than any other type of silicone. On the cam towers I use a heavy enough bead to squeeze out slightly on the edges when tightening down the tower. I leave this bead on as an extra sealing precaution.

Hylosil is a bit harder to find. If your local supplier can't order it for you, Pegasus Auto Racing Supplies has it.

Neal also reports that some of the aftermarket half moon seals shrink a lot after only a matter of months and create a leak, while the genuine Jaguar half moon seals don't shrink enough to cause a leak if installed as described above.

Intake Manifold Gaskets

When installing the intake manifold gaskets, Chad Bolles suggests:

Though you do not really have to seal the intake gaskets, I do anyway. I use a non-hardening sealer that I get from a GM dealer, part no. 1050026. I have spent almost 30 years racing automobiles and have found that this sealer really does not get hard. On my race engine I have even used the intake gaskets over again, cause they just peeled right off with no tearing. I am sure somebody will say use silicone, but I have found that removing it is a pain in the butt.

Leaky Oil Drain Plug

In general, soft copper drain plug washers should not be reused, as the copper gets hard and fails to seal. Fiber washers seem to work fine as long as you don't use those quick-oil-change shops, where the gorillas will tighten the drain plug with a power tool and break the fiber washer. Michael Neal suggests:

Use a metal washer with a type of silicon rubber bonded to the inside. They are reusable and last for several years. For the XJ-S the part number is EBC4896. These are seals for the banjo bolts on the transmission cooler lines and they are worth the US$4.

Oil in Air Intakes

Robert Dingli explains the oil that always seems to collect in the air filter housings and around the butterflies:

What you are noticing is probably a mixture of a small amount of engine oil that has been forced out as a vapour from the crankcase by blowby gas which has then condensed within the inlet manifold. You may also get some residual fuel (usually the heavier fractions) leaving an oily film. This is normal even for new engines but will tend to get worse as the engine wears.

On engines which have the inlet manifold sloping down from the head, there is usually quite a puddle sitting in the plenum. The first time I noticed this was when one of the vacuum lines became blocked. It turned out to be the line which connects to the underside of the plenum. I have since rerouted that line and plugged the connection. Whenever I remove the plug, a thick deep red oily mess dribbles out. The red colour is obviously the remnants of petrol (leaded petrol in Australia is coloured red) which has run down into the plenum after the engine has been stopped. The lighter fractions tend to evaporate when the engine is next heated.

Very occasionally, I have been known to pour a small amount of petrol into the plenum to dissolve the goo and then drain from the lowest point.

Oil Leaks at Filter Head Assembly

Peter Smith says:

I replaced the O-rings leading into the head assembly without any benefit -- the oil would gather around the top of the filter less than a minute after starting the engine. I eventually took the head assembly off and found a blanking bolt fitted to the rear which had a failed fibre sealing washer. Replaced it with a copper washer -- no more leaks. I had to take the head assembly off to see the bolt but when you know it's there it may be possible by feel.

Oil Pan Removal

The crankcase bottom is actually two pieces, a pan and a sandwich plate. The pan, which exists only at the rear of the engine, comes off easily enough. However, any hope that this will get you anywhere is quickly shattered. The crankcase is fully baffled (necessary to prevent foaming, reduce heat buildup and power loss, and insure proper oil flow to the pickup in a high rpm engine), and there is one baffle the length of the engine that cannot be removed without removing the sandwich plate.

Contrary to the manual, the sandwich plate can be removed without pulling either the front suspension assembly or the engine out of the car. It's a real pain, though, so you might still consider one of those options. To remove the sandwich plate:

1. Unbolt the steering rack without disconnecting hoses, steering column or tie rods. Lower the rack a few inches and let it hang there.
2. Remove the fan to allow the engine to be raised without hitting the shroud.
3. Remove the nuts from the two main engine mounts, and use a hoist to lift the front of the engine as far as possible.

With all this done, the sandwich plate will just barely come out rearward. Putting it back in, with new gasket in place, will also be a lot of laughs.

While you're in there, replace all the O-rings you can find, such as those in each end of each oil tube. If they leak, they just leak into the crankcase, but each leak reduces oil flow to the engine.

Compression Check

First, a brief description of how to properly perform a compression check on any car:

1. The battery and starter must be in good condition.
2. ALL of the spark plugs should be removed.
3. Power to the ignition system should be disconnected, since an electronic ignition system may be damaged trying to fire with the spark plugs disconnected.
4. The throttle should be held at least part way open, usually by jamming something in the linkage.
5. On a car with EFI, it would also be helpful to disconnect the power to the EFI system or fuel pump to prevent fuel flow.
6. With a compression gauge fitted to one spark plug hole, the engine should be turned on the starter through several compression strokes, until the reading stabilizes at a peak value.

On the XJ-S, it would be most helpful to have the type of compression gauge that screws into the spark plug hole and has a lengthy hose. Trying to hold the press-in-place type on this engine is not easy. Also, since the A/C compressor has to be removed to get at the front plugs, you will have to run the test with a dangling drive belt; try to position it so there is no tension on it, and the crank pulley can turn within it without driving it.

On the pre-H.E. engine, the readings typically will be about 130-150 psi. The H.E. engine has 11.5:1 compression (U.S.), and will read about 200-220 psi. Note that readings will be lower at high altitudes.

Keep in mind, however, that the absolute values are not as important as the relationship between them. There are dozens of factors that could affect the absolute values (including the calibration of your gauge) so if your readings are all a little higher or lower than the above, don't worry about it. But they should all be nearly the same; one significantly lower than the others is not a good sign.

If one cylinder reads low, it is customary to add a couple tablespoons of motor oil into that spark plug hole and test it again. In theory, the oil will temporarily seal bad piston rings but won't seal a burned valve, so this test may indicate the level of disassembly needed. Of course, the oil probably won't seal a burned piston or a hole in a cylinder liner, so the results are best taken with a grain of salt. Either way, the head has to come off.

Leakdown Test

The leakdown test is gaining in popularity among mechanics, who feel that it gives a better indication of the actual quality of the sealing of the compression chamber than the compression check. To perform a leakdown test, compressed air at a known pressure (usually 100 psi) is fed through device with an orifice in it and into a cylinder via the spark plug hole. The pressure downstream of the orifice is measured, and the leakdown rate is calculated as the percent which the pressure dropped across the orifice. If the leakage out of the cylinder is very low, the pressure after the orifice will be very close to the pressure before the orifice, and the percent of pressure lost will be low. If the compression chamber has big gaping openings in it, the main restriction in the flow will be the orifice itself, and the pressure after the orifice will be closer to ambient -- and therefore the percentage lost will be much higher.

Note that, when doing such a test on the Jaguar V-12, it'd be a good idea to take the oil filler cap off the left cam cover. We wouldn't want a well-sealed crankcase (hah!) to cause unwarranted favorable readings.

It's entirely possible that the leakdown test is highly regarded simply because it gives results in percent. It should be pointed out, however, that the percent has no real basis and is entirely dependent upon the size of the orifice in the test device -- and Randy K. Wilson says "and there is no such thing as a standard orifice size." In order to be able to compare the results of one leakdown test against another, it would be necessary to confirm that the orifices used were the same size and had exactly the same flow characteristics and that the same air pressure was used for the tests.

Wilson adds:

Next question is: how much air leakage is acceptable? This all depends on how big the cylinder is. The bigger the bore, the more ring area there is to leak by. Typically, the valves are bigger, too. Here we could really use a percent of leakage vs. base volume, but our tester is effectively measuring finite volume of flow.

There are other concerns involving leakdown tests. For one thing, since the engine does not turn during the test, it really only gives an indication of the leakage at one piston position. While this is usually adequate, it may fail to identify certain types of problems such as localized damage on a cylinder wall. Perhaps the careful mechanic could slowly turn the engine over by hand while doing the leakdown test, and watch the gauge for variance in the readings.

The leakdown test does have the advantage, however, that if the same mechanic is using the same leakdown tester at the same pressure all the time, they can get a real good idea of just what condition cars are in. While compression readings will always vary from car to car, the percentage readings from his trusty leakdown tester should give very consistent indications on cars in similar condition regardless of compression ratio or other variables.

Head Gasket Check

Michael Neal suggests two methods of checking the integrity of the head gaskets. First, remove the rubber hood that connects the PCV system to the engine just forward of the oil filler cap, and look inside it. Milky deposits are an indication that water is getting into the oil, usually a sign of trouble.

For a more definite check, Neal recommends removing the spark plugs, pressurizing the cooling system to 15 psi, and leaving it overnight. Then have someone turn the starter while watching the spark plug holes. Mist (or worse, a solid stream of water) coming out of a plug hole means it's time for engine work.

Of course, pressurizing the cooling system usually calls for a special tool. It basically is an adapter radiator cap and a hand pressure pump; Stant is the common manufacturer and it runs US$60 to $70. In a pinch you could tee into the small hose on the center fill pipe and apply pressure.

Crankshaft Pulley

First note that, contrary to the repair manuals, it is not necessary to remove the crank pulley to get the water pump off.

Removal

To loosen and retighten the large bolt holding the crankshaft pulley on, it is necessary to hold the crank still. Here we have a veritable cornucopia of suggestions. You can remove the starter to jam the flywheel, but that is definitely the hard way. An easier way would be to use the access hole on the left side of the engine, the one with a rubber plug and intended to provide access to the torque convertor mounting bolts. Michael Neal provides an even simpler access: just remove the cover from the bottom of the torque convertor housing.

Matthias Fouquet-Lapar suggests:

You don't need to jam the flywheel. Once you have removed the upper part of the pulley (the one which drives 3 belts), you can easily use its 2 screws to attach a home-made bar on the damper.

Mike Cogswell suggests:

You can weld a short length of rod to the end of an old spark plug. Use it to replace a plug, hand rotate the engine (breaker bar on that bolt you're trying to remove) until the piston is up against the rod. Now it's locked for sure. Just make sure you disable the starter and hang a red tag so it can't get turned over with the rod in it. You do need to be very careful about valves. Obviously if the rod interferes with the valves you could easily damage a valve and create a lot of work for yourself.

Some suggest this method risks damaging the piston, plug threads or other engine parts if the torque necessary to remove that bolt is too high; to minimize this concern, the device should be long enough to obstruct the piston a good ways below TDC, since near TDC the leverage is not favorable for this job. This method does have the advantage that the same tool may be usable for calibrating the timing marks on the bottom of the engine.

Jeffrey Gram (who doesn't care for the above suggestion) writes:

To fill a cylinder with concrete works well also, but oil is better...

Ryan Border says:

I always thought the trick for this was to fill the cylinder with nylon rope through the spark-plug hole. Soft enough not to damage anything, but "rigid" enough (when it's all bunched up by the piston) to work some serious force against.

Note: make REAL sure you're on the compression or power stroke and not on an intake or exhaust stroke -- having open valves can bend them.

Shane Mantoszko says:

Use a good long handled socket/torsion wrench, put it on the front crank nut, brace it on a strong part of the engine bay, disconnect the coil, and then turn your ignition key for a few quick bursts, and viola, the crank nut will be loose....hard part is then re-tightening it, but a ratchet gun worked for me.

Of course, on my car I can just put it in 5th gear with the emergency brake on.

Woodruff Key Problems

Paul Konitshek and Michael Neal report that the woodruff keys that align the crankshaft damper/pulley are a known problem area. The keys may become worn or totally sheared, allowing the pulley to reposition itself around the crank. This becomes only too apparent when trying to set the ignition timing according to the marks on the pulley.

Note that there are two keys used. There is a "split cone" that is similar to those used on industrial pulleys. The pulley fits onto the outside tapered surface of the cone and is aligned with one key. The cone slides over the crank and is aligned with another key. When the bolt securing the pulley is tightened to specification, the split cone compresses securely onto the crank like a collet in a chuck.

Neal reports:

The woodruff keys on the crank pulley do have a bad history. It almost never gets to the point where the pulley comes loose. It seems only to happen if water has gotten into the nosecone on the crank. The area is always very rusty when the front pulley is removed. The woodruff key is either broken or eroded away from the rust. In some cases the slot in the crank is widened a bit but a new key usually secures it substantially. By the way, I have never seen the rubber dampeners on the pulley on either the XJ-S or the XJ6 fail.

Timing Cover

If you want to remove the timing cover to replace the front oil seal, don't waste your time. The front oil seal presses in from the outside, and Jaguar even provided some prying slots for removing the old one.

Removal

If you do need to remove the timing cover, Section 12.65.01 of the Jaguar "Repair Operation Manual" lists 13 steps, the first two of which are as follows:

1. Remove engine and gearbox assembly from the car.
2. Remove cylinder heads from the engine...

Fortunately, there is an alternate method. To remove the timing cover with the engine still in the car and the heads in place, proceed as follows:

1. Remove the belts, fan and its mounting bracket, A/C compressor front bracket, and all the other ancillary stuff in the way.
2. Remove the front crank pulley. NOTE: What looks like a bolt head in the center of the crank pulley is actually a hex fixture for turning the engine by hand. Two smaller bolts must be removed to remove this hex, and the real pulley retaining bolt is underneath.
3. There are three studs threaded into the timing cover that protrude upward through the front edge of each head. Remove the nuts and washers, then grab the studs with a pair of Vice-Grip pliers and unscrew them. NOTE: some of the studs are trapped and cannot be removed; once these are unscrewed, merely retain them in a raised position while the cover is being removed. Once the cover is off, they can be removed.
4. The timing cover is essentially pinched between the heads and the sandwich plate. Michael Neal, who is a Jaguar mechanic and uses this method regularly, says:
   I loosen as many of the sandwich plate bolts near the front as possible. I believe it works out to about 4 or 5 back, going between the subframe and the motor. I then use a Snap-On medium sized ladyfoot prybar and go in the hole where the oil cooler adapter bolts onto the sandwich plate. I pry against the bottom of the tube that the adapter goes into and the inside of the sandwich plate. This pulls down the right front corner of the sandwich plate and allows some space for the timing cover to move. The prybar over-centers and locates itself while holding the plate down. It is very important not to pull down too far. The bolt holes are very prone to cracking and the break will spread out toward the center of the sandwich plate.
   See the section on Oil Pan Removal if you wish to remove the sandwich plate entirely.
5. Remove the retaining bolts and remove the timing cover.

Reassembly

1. Since your studs were all boogered up by the Vice-Grips, buy new studs with the same threads but longer. Saw or grind them off until they are 1/4" longer then the originals. Then, grind flats on this 1/4" to ease the reinstallation and any future disassembly. Be sure to clean up the threads so the nuts go on easily. Remember to slide the trapped studs in place before installing the timing cover. Be sure to use anti-seize compound on all studs.
2. Before reassembly, carefully trim the timing cover gaskets flush with the upper corner of the timing cover.
3. Since the head gaskets are not being replaced, it is a good idea to apply some sealant to the bottom of them to help them seal against the timing cover. The only stress on this portion of the head gasket is a slight crankcase vacuum; the integrity of the head/block seal is unaffected. Make sure to apply sealant in the corner of the two mating surfaces.
4. Michael Neal provides this tip for getting the timing cover back in between the heads and sandwich plate:
   On reassembly I use .003 thousandths sheets of shim stock on the upper surface of the sandwich plate gasket and the underside of the front of the headgaskets. You have to trim the stuff to clear, but it prevents damage to the gaskets and lets the timing cover slide back in easily. The headgaskets are...very prone to wrinkling if you don't use the shim stock pieces to slide the cover back in.
5. When threading the new studs into place, remember there is no reason to tighten them into the timing cover. As long as they have been threaded in several turns, the nuts will torque properly. Tightening the studs into the timing cover merely makes them harder to remove next time.
6. During reassembly, progressively tighten the timing cover bolts along with the nuts on the studs. The cover must be brought up against the heads as it's being pulled against the block. Tightening one set before the others will cause leaks.

Timing Chain Tensioner Access Cover

The access to the timing chain tensioner latch is via an opening on the front of the engine, forward of the right side head. The purpose of this access is for locking or releasing the tensioner during overhauls; there is no need for periodic adjustment, as the tensioner is self-adjusting.

The rubber plug always seems to get hard and crumbly. People with the new one in hand sometimes assume there was a material change, since the new one is soft and pliable while the old one appears to be Bakelite. Looking at the ears on the new one can also lead one to believe that it's a push-and-turn type of cover, like a radiator cap. No such luck; it's a simple round hole, and the ears are supposed to be flexed to get it in and out. The old one will probably have to be removed in pieces. If a piece or two fall down inside, don't worry about it, they're too soft to do any serious damage. They'll probably just come out in the next oil change; it's definitely not worth further disassembly.

Note that this is an opening into the crankcase and should be fairly well sealed to prevent oil vapor leakage and keep the PCV system working properly; Chad Bolles suggests:

...apply a thin coat of GM Gasket Sealing Compound part no. 1050026 (stuff never gets hard) and press in the new plug and you are good to go.

Jim Isbell didn't like how much grief was required getting the plug out after it had dried up, and determined it wouldn't happen again.

I have cut the tabs off of the rubber plug that fills the adjustment hole for the chain tensioner. I have made a simple aluminum "L" shaped piece that fits under a water pump bolt and holds the plug so it wont fall out.

If desired, the opening may be plugged with a compressible rubber type freeze plug. This may even be preferable to the original plug, since it will make an airtight seal. Be sure that the plug does not interfere with the timing chain or the operation of the tensioner.

Timing Chain Tensioner

When XJ-S owners are old and gray and sitting by the fire with their grandchildren around them, one of the pleasant memories they will inevitably want to share will be of their first encounter with the V-12 timing chain tensioner.

Sarcasm? You bet! If you manage, on your first try, to retract the tensioner and reengage it successfully without breaking this tensioner, you should consider yourself lucky. The timing chain tensioner in the V-12 apparently works well when new but gets brittle with age or heat, and an old one can be broken very easily. Michael Neal, who works on Jaguars every day, says:

I've become so paranoid of old tensioners, my failure rate has been very high as of late. I'm not too surprised though, most of the cars have been approaching ten years old. I've been as careful as possible, knowing exactly what I was doing, and have watched the damn thing crack on one of the pivots.

Obviously, if you have the timing cover off for other reasons and the tensioner is intact but has a few years on it, it may be advisable to replace it anyway.

Description

I will first attempt a description of the tensioner, since it is well hidden and its configuration may not be apparent until it is too late. Basically, the tensioner consists of a plastic arch that the timing chain slides over top of on its way from the crankshaft sprocket to the right side cam sprocket. This is the slack side of the chain, so it's the proper place to put the tensioner. Between the legs of this arch is a spring that pulls the legs together, making the arch steeper and taller and therefore taking up slack in the chain. The end of the arch nearest the crankshaft is located by a pin on the block, while the end near the cam sprocket has a steel foot attached that is free to slide up and down on the inside of the housing as the arch changes shape.

Alongside the spring is a latching assembly that consists of a rod that is attached to one leg of the arch and passes through a hole in a rocking latch attached to the steel foot on the other end of the arch. The aforementioned spring is actually attached to this rocking latch, slightly off center, so that it not only applies tension to the chain but also causes the latch to rock in the CW direction (as viewed from the front of the car facing rearward). This assembly serves two purposes: First, the rod going through the hole in the rocking latch makes a very effective one-way lock; the rod can easily slide in the direction that allows the tensioner to take up slack, but it CANNOT back up and allow more slack. Second, when the mechanic has manually retracted the tensioner, a step at the end of the rod provides a catch for holding the tensioner in retracted mode while working on the car.

When removing the camshafts or the heads, the tension on the chain must be disengaged. However, the chain is not removed; the sprockets are simply unbolted from the camshafts and supported in place by special brackets provided for the purpose. The heads are removed in this state, leaving the chain and sprockets hanging there.

Special Retraction Tool

To retract the tensioner requires two tools, collectively known as Jaguar tool JD.50. One tool is inserted from the top of the engine where the cam cover has been removed, alongside the cam sprocket, and hooks onto a hole in the steel foot at the top of the tensioner; this tool is for pulling the tensioner back to the disengaged position, and is shaped to rest against the top of the sprocket for leverage -- thereby providing better control. The other tool is inserted through an access hole in the front of the timing cover and is used to rock the rocking latch. The rocking latch has a slot in it, 3/8" wide by a little over 1/2" long and parallel to the chain, for inserting this tool.

Improvising both tools is fairly easy. For the first tool, a sturdy hook is required; a standard battery hold-down bolt may be a good place to start. Adding a lever that rests on top of the sprocket isn't too hard, you can even make it out of wood. Thomas E. Alberts says:

I tried the lever style tool like the manuals show and didn't like it much. I made one with a long 3/8" bolt (~12in) and a steel tube (~1.5in dia). I formed a hook by grinding away most of the bolt head, padded one end of the tube and put it against the valve cover mating surface and with a washer and a nut on the threaded end and the bolt running through the tube and into the chain tensioner, I was able to gently apply the required tension. It worked well.

For the rocking latch tool, it appears that a common screwdriver may be used, but that really doesn't work well. A better idea may be a standard "brake tool" the lever used to turn the star wheel on self-adjusting drum brakes. You might also check to see what you have in tire irons, especially those intended for bicycles. And of course, one of those right-angle screwdrivers might work, especially if you can find a large one. If you want, you can easily make a very suitable tool: Cut a piece of strip steel 1/8" thick x 1/2" wide (commonly available at hardware stores) to a length of about 7 inches. Then, about 1-1/2" from one end, make a sharp bend of just slightly less than 90 degrees.

Before actually getting into how to use the tools to retract the tensioner, a note: If you drop anything down into the timing cover, you're not gonna be any fun to be around for DAYS. It is highly recommended that every part, tool, wedding ring, or whatever that is anywhere near the openings around the timing chain have a string tied to it.

Disengaging the Tensioner

The actual operation of disengaging the tensioner requires using both tools simultaneously. To begin with, I suggest using the latch tool by itself to try rocking the latch counter-clockwise just to get the feel of it. It will not rock very far, but it shouldn't take too much force to rock it, and you should be able to feel the spring. Old tensioners always seem to have bent or damaged rods or latches, and it's difficult to imagine how the damage occurs other than people applying GREAT force to this rocking action. You should also note that, if everything is working properly, rocking this latch alone will have no discernible effect -- no clicks, pops, clangs, or anything else.

Don't bother testing the other tool by itself. Trust me, you won't be able to move the tensioner toward the retracted position without simultaneously rocking the latch counter-clockwise -- unless, of course, the tensioner is already broken.

Now, to actually retract the tensioner: First, rock the latch counter-clockwise and hold it rocked; it doesn't need to be held hard counter-clockwise, just so that it is prevented from returning to the clockwise position. With the latch so held, pull up on the retracting tool; you should feel it smoothly moving against a fairly stiff spring tension. In order to lock the tensioner in the retracted position, you will need to pull as far as it will go. At this point, it should suddenly become possible to rock the latch much farther in the counter-clockwise direction. While holding the latch firmly in this full counter-clockwise position, carefully release your pull; it should lock in that position. Once it does, you can rest assured, it won't move by itself, you can go on and do other things.

Engaging the Tensioner

When it comes time to engage the tensioner, do not simply trip the latch to restore the tension; the tensioner will shatter like a dried twig, and you will need several bottles of high-octane elixir to get over it (see the section on timing cover removal). Use the special tools to gradually release the tensioner into its normal position. Pull on the tensioner while rocking the latch in the clockwise direction, and gradually release the pull; it may take a couple tries before the latch is successfully released and the tensioner starts moving. Once it does, you may quit fiddling with the rocker altogether, it'll take care of itself, but continue to use the puller tool to gradually allow the tensioner to assume its final position.

Avoiding Breakage

Now, on to a suggestion for disaster avoidance. Jaguar designed the latch so that the tensioner must be retracted as far as it can possibly go before it can be locked in the disengaged position. This bends the plastic arch, normally fairly curved, into a nearly straight shape -- and therefore stresses it far beyond what it normally sees. For several operations on the engine (such as camshaft removal), it doesn't matter how much slack is available, only that the tension is gone. If this is the case, retracting the tensioner only part way would suffice -- if there was a way to hold it there. If the right side tappet block is not to be removed, this may in fact be fairly easy. Whatever homemade tool is used to retract the tensioner can also be fashioned to hold it retracted, possibly by providing a small block of wood with a hole in it that sits over the opening and using threaded rod to make the hook.

If the tappet block must be removed, obviously a little more ingenuity would be required. At this point, it'd probably be best to just go ahead and use the intended latching mechanism and hope for the best.

Timing Chain Dampeners

These are the steel plates mounted alongside the chain along several of the straight sections between sprockets. The repair manual suggests using quick-drying paint to mark their locations before removal. Failing this, the use of an elaborate (and undoubtedly expensive) special tool is required to properly position them.

You already moved them? Sorry, at present I can offer no help. I am including this section to describe what they are and how they work.

A roller chain is a fairly decent and reliable drive mechanism at low speed. However 6500 rpm is another story; at higher speeds chains can whip, flutter, buzz, and otherwise dance around their path around the sprockets. At certain resonances, a chain whipping back and forth can cause very high tension stresses, resulting in damage to the chain, sprockets, camshaft bearings and tensioner.

These plates are designed to prevent this. If the chain is moving smoothly and along a straight line like it should, it shouldn't even touch the plates. But if it starts to whip, it hits a plate -- which absorbs the energy of the whip, and allows the chain to return to a calm motion.

Based on this theory, it would be logical to assume we could just bolt the plates on so that they are immediately adjacent to the chain without touching it. There are a couple problems with this plan. First, if you follow the official Jaguar assembly order, the plates must be installed and the timing cover bolted up before the heads are installed, so having the chain in place -- meaning the tappet blocks, camshafts, and camshaft drive sprockets in position -- is not possible. Of course, you could always trial fit the heads, tappet blocks, camshafts, sprockets, and timing chain in order to set the plate positions, then tear it all apart again.

Earlier I described how to remove the timing cover with the heads on and therefore there may be an opportunity to adjust the dampers with the chain in place -- although it may be a rare case when the plates need to be positioned but the heads DON'T need to come off.

The second problem is that I'm really not providing enough information for proper positioning. I'm only providing the theory; presumably, during development of this engine, the optimum positions of these plates was precisely determined, and they may be far more critical than simply "close to the chain without touching it." Improper positioning of these damper plates could be catastrophic, causing a broken timing chain which in turn causes pistons to impact valves in open position. You see, the real purpose of this section is not to save you effort; it's to encourage you not to assume the position of these plates is unimportant, skip important steps, and cause yourself a great deal of heartache down the road.

Timing Chain Replacement

The timing chain in the Jaguar V-12 is a conventional double-row roller chain. Typically, the wear on chains of this type is much more significant than on the sprockets, and usually the chain can be replaced without replacing the sprockets. This is in sharp contrast to the "silent" timing chains used in many American V-8's, where it is customary to replace the timing chain and sprockets as a set.

Another characteristic of typical roller chains is that wear on the sprockets increases with the use of worn chains; if the chain is renewed regularly, the sprockets can last almost indefinitely. The Jaguar timing chain is so cheap that it is recommended that it be replaced whenever the engine is disassembled far enough to do so. The sprockets are so expensive that you will want to do whatever it takes to keep from having to replace them.

In general, the sprockets don't need replacing unless an inspection shows signs of serious wear -- one side of each tooth looks different from the other side.

Per Jan Wikström,

According to a Reynolds chain handbook that I mislaid some time back in the seventies, so my memory may be slightly off here, the way to determine whether a sprocket warrants replacement is to hang the new chain over the sprocket and apply a strong pull (that's an Imperial strong pull, not a US strong pull!) in the normal drive direction. If more than three links ride up noticeably on the teeth, the sprocket is too worn.

Camshaft Sprocket Removal

The V-12 has a cute little bracket just forward of the camshaft sprockets that holds the sprockets (and timing chain) in place during removal of the heads or camshafts. The sprocket hubs have little stubs to sit on these brackets, and slots for a clip to secure the sprocket on the bracket.

The clip, a special tool, can obviously be improvised with sheet metal or even a normal C-clip. It must be suggested, however, that whatever is used have a string tied to it with the other end tied to your finger. If the clip falls down into the timing cover while you're trying to put it on, see the section on timing cover removal.

Camshaft Timing

The repair manual describes how to adjust the camshaft timing; this is just some clarification. To adjust the camshaft timing, obviously the chain can be moved over one tooth on the sprocket -- an extremely coarse adjustment. The camshaft sprockets have a splined inner hub that contains the four mounting holes. A circlip can be removed, allowing the separation of the inner hub from the sprocket, and the hub can be moved over one spline -- a fairly fine adjustment. However, the hub has an odd number of splines, so rotating the hub 90°, 180°, or 270° will effectively relocate the four bolt holes in 1/4-spline increments -- an extremely fine adjustment.

The engine is designed so that the crankshaft and the camshaft can be located where desired, the timing chain put in place and the tensioner activated, and then the mechanic can fiddle around with the sprocket hubs until the bolt holes line up. Jaguar provides an alignment notch on each camshaft and a special tool for setting the camshaft position. This special tool, C3993, costs under US$20 and is not easily improvised. It is recommended that anyone who has an engine apart far enough to use one have it on hand.

If the engine in question has a few miles on it, it may even be a good idea to go through the procedure of setting the camshaft timing while there. Wear in the timing chain will cause the camshaft timing to gradually move. What's worse, the timing of the right camshaft will move more than the left.

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.

Mike Morrin adds:

I cannot believe the figure in the Jaguar manual. The endfloat on the gears in my pump was over 0.020 inches. 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 fingures. 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 V-12 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 US$45 plus some additional bolts are required.

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. Having a dealer perform this work reportedly costs over US$600, and is probably a reasonable charge considering the number of hours that will be required.

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.

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 few seconds 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 each, but most of the wear involved here occurs at startup.

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 V-12, 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.

Bearing Failure Modes

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 V-12 is no exception, and sometimes shows lower oil pressure when hot and idling, especially when it has a few miles on it. The V-12, 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.

Low Oil Pressure

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.

Oil Thickeners

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 Pressure Relief Valve

If you have an opportunity, it is recommended you disassemble your relief valve assembly. First, check for galling in the cylinder; if found, some gentle honing will usually render the valve serviceable. The plunger should move freely without jamming.

Second, there is a single washer under the spring. It is suggested that an additional washer or two be inserted under the spring to raise the opening pressure somewhat.

Make sure that all O-rings in the assembly are in place and in good condition. Be careful not to strip the threads on the bolts when reassembling, as they are tightened against the spring pressure.

Oil Filter Replacement

The oil filter on the Jaguar V-12 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.

Different Filters

It has been noticed that some filters for the V-12 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 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

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

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.

Mike Claus forwarded this info he found on the WWW: 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.

Perhaps most XJ-S owners would consider adding a bypass filter extreme; perhaps it is difficult to find enough space in the XJ-S engine compartment. But the discussion nevertheless illustrates the importance of oil changes and quality oil filters.

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 "PreLuber" on my van because it only gets driven about once a week or so, and the prelube 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. If that isn't clear enough, see: http://riem.com/disk$user_diskI/http/Snake_Oil.txt

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.
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.

Cylinder Head Removal:

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.

Cylinder Head Nuts

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 several head nuts on the Jaguar V-12 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.

When using crowfoot wrenches in conjunction with a torque wrench, the crowfoot should always be attached to form a 90° 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.

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 US$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 US$4,000. The job of replacing two pistons and liners cost the author less than US$1,100 for parts in 1989. Any mechanic brave or knowledgeable enough to tackle the job can probably overhaul the engine for US$2,000 plus labor, depending on the damage involved.

Pistons & Cylinders

In general, you can buy pistons for the V-12, 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.

Cylinder Wear

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.

Piston Sizes

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 V-12 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 V-12, the piston to bore clearances for cylinders 1A through 5A and 1B through 5B is .00045-0.005, whereas the clearance for piston to bore in cylinders 6A and 6B is 0.0055-0.006.

These absolute values may be of little use to the normal V-12 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 200,000 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 US$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 invalid 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 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 1.

Figure 1 - Rear Main Bearing Sealing

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.

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. Also, please note comments in the Engine Modifications section.

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 Belt Tensioner

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

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: V8 Engines

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 (like Jaguars That Run) that offer kits for replacing the Jaguar V-12 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.

V-8 Engine Design

The 90° 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:

• 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
• 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 recently introduced V-8 engines with overhead cams and intelligent camshaft drive systems, apparently in response to competition from Lexus and Infiniti.

Jaguar's Opinion

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 V-12.

Valve Train Noise

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

 

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