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Engine Maintenance

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Engine Maintenance


H.E. VS. NON-H.E.: The H.E. (High Efficiency) engine, with 11.5:1 compression (12.5:1 outside the US) 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 "V12" emblem. In 1986, the H.E. emblem was unceremoniously dropped and a V12 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: The engine number is stamped on the top rear center of the block just forward of the joint with the GM400 transmission bellhousing, but it is typically hard to find because it is covered with grime. Paul Hackbart sends this tip: "Take your oil dipstick out and get on the passenger side of car. You can stick it through near the oil pressure sender and scratch away until you see it. Just make certain you clean it off afterwards."

The XK's Unlimited catalog includes a guide of engine numbers for the XK 6-cylinder and the V12. It provides the following info on the V12:


E-type Series III



XJ12 Series I



XJ12 Series II

1973 (Carbs)


XJ12 Series II

1974-79 (EFI)


XJ12 Series III




up to 1980




For more detail on XJ-S engines, Richard Mansell sends this helpful data from "The XJ-S Collectors Guide":



Feb 76

Canister type oil filter introduced


Oct 76

Revised EFI


Modified fuel pump


Apr 77

GM400 introduced


Nov 77

Stronger manual trans selector shafts


May 78

Modified air filter box to stop blowing off!!


Oct 78

Ignition amplifier re-located


Oct 78

Twin V groove water pump pulley introduced


Nov 80

Digital P injection introduced


Nov 80

Sump plug relocated


Jul 81

HE Introduced

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



Metric threaded cylinder heads


Piston spec modified


Inlet manifold modified to remove holes for cold start injectors


Modified drive plate


Spark plugs changed from B6EFS to BR7EFS


Sump oil baffle plate changed


Water pump bearing size increased


Full flow oil cooling replaces relief flow


GM400 revalved, modified sump pan


5.3 vs. 6.0 LITER: The Jaguar V12, 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.

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 V12 was designed to reestablish Jaguar's eminence as a world-beater in the racing community (and prior to the fuel crisis of the early 70's), hence the considerably over-square design. It was quite successful in this regard, still winning LeMans races in the late 80'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 displacement 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 V12 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 V12 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 to 11.0:1.

Tom Walkinshaw Racing (TWR) was offering 6.0 litre engines much earlier. According to Richard Mansell, "TWR started making ësporty' XJ-S's in 1984. One of the options then was a 6.0 litre engine." John Goodman reports that TWR also made 6.2 and 6.4 litre versions, and maybe even a 6.7.

Later on the JaguarSport XJR-S also had a 6.0. Mansell: "When JaguarSport officially started producing the XJR-S in 1988 only a 5.3 litre engine was available. It was not until mid-89 that the 6.0 litre was introduced as standard. This was then discontinued in 1993 as by then the standard XJ-S now had a 6.0 litre engine."

Note, however, that the 1993-on updated engine has a lot of other features these earlier engines lacked, such as a revised bolt pattern for connecting the GM400 transmission.


WHAT'S IN A REDLINE?: Some people, probably accustomed to American pushrod V8's, feel that the 6500 RPM redline marked on the tach is really aggessive and far too high for an engine this big for everyday use. Nothing could be farther from the truth; this is not an American pushrod V8, it's an OHC V12 with an unusually short stroke. Roger Bywater, who worked in the engine development department at Jaguar when this engine was designed, provides a more realistic understanding of just what that 6500 RPM redline is all about: "6500 r.p.m. is certainly safe and 7000 would not be a cause for concern. In fact I know of basically standard 5.3 V12s cobbled together with second hand bits being taken to near 8000 in race cars without suffering any problems at all. On the other hand an elderly engine does deserve a certain amount of respect. I expect the one thing that would result is that the timing chain and tensioner would start to show signs of distress a bit sooner if subjected to continual high r.p.m. In reality, there is not much point in revving a standard V12 beyond 6000 because it will be running out of breath anyway and therefore won't be making much power.

"The real problem taking these engines to 6000 and above is that the GM 400 torque converter distorts under centrifugal loads so that the blading can make contact creating fine metallic particles which then cause accelerated wear of the transmission. A way around this is to use a furnace braized converter which is more rigid and able to tolerate the higher r.p.m. without distorting so much."


END OF AN ERA: The final Jaguar V12 engine was built April 17, 1997.


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.

Tips on improving post-shutdown cooling are in the section on Cooling System Upgrades.


KNOCKING/PINGING/PINKING/DETONATION/WHATEVER: Regardless of what you call that sound, it ain't good for an engine. A brief description of what's going on: When an engine is running properly, the fuel/air mixture within the cylinder is ignited by the spark plug and the flame front grows continuously and spreads throughout the combustion chamber until the entire charge has been burned. However, while this is going on, the piston is moving upwards towards the head, compressing the charge and thereby heating it. In the most severe cases of knocking, the compression causes the charge to self-ignite before the spark plug even fires. The result is that the entire charge ignites at once, rather than the gradual ignition of the flame front moving through the charge. This "explosion" has been likened to hitting the piston with a hammer. It can damage the piston, connecting rods, and the bearings in both ends of the con rod.

What usually happens is less severe, however. The spark plug fires well before the piston reaches the top of its stroke, so the flame front has begun its travel while the compression is still in progress. Since the burning charge is expanding, it is compressing the unburned charge into the far corners of the combustion chamber. The combined effects of the piston rising and the flame-induced pressure causes the remaining portions of the charge to self-ignite. The actual amount of charge exploded in this fashion can vary anywhere from a tiny portion to the entire charge, so knocking can be either severe or barely detectable.

There are many factors that contribute to knocking. The most notorious is compression ratio; the higher the compression ratio, the more likely it is for the charge to be detonated. Another key issue is the octane of the fuel, which is a measure of how hot it must be before it self-ignites; the higher the octane, the hotter the mixture must get before it will burn. And the timing is critical, since lighting the mixture too early will cause too much of the charge to be burned before the piston gets to TDC and the high pressures will cause detonation.

Other factors include the intake air temperature, the fuel temperature, and cylinder wall and head temperatures. EGR, which puts some inert gases into the mixture, makes it harder to ignite and therefore reduces the tendency to knock. Also, there are some minor details that can complicate the issue; sharp edges in the combustion chamber can act as "glow plugs" and ignite the charge prematurely. Carbon deposits can increase the compression ratio, as well as provide glowing embers to preignite the charge.

Knocking can be difficult to detect on the Jaguar V12. All those little cylinders mean that each knock is small, and all that sound deadening built into the car keeps the driver from hearing much of anything in the engine compartment. Basically, if you can hear it at all, you might need to be concerned. On the other hand, Mike Wilson reports: "I asked the local Jaguar rep and he had the audacity to say that "All Marelli cars ping". He said it was even in the owners manual! So, I came home and read mine and sure enough, there it was in black and white! It said that a small amount of pinging was normal and if it happens on flat roads under no load, to see your dealer for further assistance."

If something needs to be done about pinging, the usual reactions include changing to better octane fuel or retarding the timing. On the later XJ-S with Marelli ignition, you can't adjust the timing by just rotating the distributor, so a jumper was provided that can be pulled to put the system onto a more retarded map when needed. Even if we try to buy good fuel, occasionally we always seem to get a tankful of real crap, and this jumper is a handy fix to get us to the next fillup.

Joe Ziehl shares some experience: "My mechanic told me to first try a higher octane fuel because while retarding the timing may help, the preignition might be caused by something other than sparkplugs, such as carbon in cylinders or on pistons. He also recommended that I treat the gasoline and run the car hard for a few days. This made a significant improvement in the pinging."

Jeff Elmore reports: "I had been getting some slight pinging under medium acceleration after the car had warmed up. I had tried many things, including checking the timing, high octane gas, etc. Then I tried the temperature at the thermostats. It was 213F on one side and 203F on the other. I just changed the thermostats and topped off the coolant (almost half a gallon low), and the pinging is gone. The car now runs better as a result, with my guess being that a lower CWT sensor means more fuel and power."


UNLEADED FUEL: XJ-S owners in the US have been using unleaded fuel for decades, but many owners in other countries are only recently facing the prospect of leaded fuel being no longer available. Since some of their owner's manuals specify the use of "Four Star" leaded fuel only, they are understandably concerned.

Addressing this concern, Roger Bywater of AJ6 Engineering (and formerly with Jaguar Engine Development) wrote an excellent article for Jaguar World magazine, Vol 10 No 3, January/February 1998, page 42. Some of the high points are summarized here.

There are two reasons for concern regarding the use of unleaded fuel: octane and valve seat lubrication. Valve seat lubrication is simply not an issue in the Jaguar XJ-S: every engine the car has ever been built with has an aluminum head with hardened valve seat inserts, and the part numbers for these parts are the same for US-spec models always intended to run on unleaded fuel. If you have shoehorned in a Chevy engine old enough to have a cast iron head with no inserts and designed to require leaded fuel, well, shame on you.

Octane is another story. The US-spec engines have lower compression ratios to run on lower octane fuel. To be able to run the high compression engines on lower octane fuel, either the compression ratio will need to be lowered or the timing will need to be retarded. If the engine is being rebuilt anyway, lowering the compression ratio (different pistons, thicker head gaskets, machining the combustion chamber, whatever) may be workable, but most people will prefer to simply retard the timing. Bywater suggests that there's very little difference between a high compression engine with retarded timing and a low compression engine with advanced timing anyway.

With the Lucas ignition systems, retarding the timing is simply a matter of turning the distributor to a new setting. Bywater says that for the 95 octane unleaded that will be available in the UK and Europe, about three degrees should do it, although as many as five may be necessary for older cars with a lot of carbon buildup. On Marelli ignition cars, retarding the timing only requires pulling a jumper to switch the ignition ECU to a more retarded timing map.

If you own an early (ë83-87) AJ6-engined car with the Lucas 8CU EFI, you can retard your timing by simply turning the distributor. However, if you have a later (ë87-on) 3.6 with the 9CU engine control system, the ignition timing is controlled electronically and not so easy to change. According to Bywater's article, there are two options: you can remount the crankshaft position sensor using the mount from the later 4.0 AJ6 engine, or you can remove the crank pulley and reposition the toothed rotor by drilling new mounting holes.


MISFIRE: With 12 cylinders, some people might not even detect a misfire. An easy way to check -- as well as to tell which bank is acting up -- is to fold a dollar bill in half and hold it over an exhaust pipe outlet and listen to the flapping that results; a misfire is usually obvious. Steven Draper adds, "According to the most recent Jaguar Repair Information Periodical, the official procedure is to use a one hundred dollar bill and send it to the dealer for evaluation. Unfortunately, the bill cannot be returned."


LEAKY GASKETS: One of the improvements Ford made to the Jaguar product line after they purchased the company was that they "Fordified" the gaskets and seals for the V12. While all of the old style gaskets look like plain paper of various thicknesses, the new gaskets are often "Gortex" sandwiched around metal or some such.

Redesigned gaskets, along with the new part numbers:


Old P/N

New P/N

Oil Filter Housing


EBC 9624

Oil Pan Gasket


EBC 9623

Cam Cover Gasket, Right C29428


EBC 9628

Cam Cover Gasket, Left C29429


EBC 9627

Thermostat Housing, Right EAC7048


EBC 8330

Thermostat Housing, Left EAC7047


EBC 8331

Valley Cover


EBC 9631

Sandwich Plate Gasket


EBC 9637

Coolant Manifold Gaskets


EBC 9634

Exhaust Manifold Gaskets C33921


EBC 10199

Throttle Body Gaskets


EBC 9635

In addition, the 12 individual intake manifold gaskets C43354 or AJM687 were replaced with two gaskets; each serves all six ports on one bank. The part number is NNA-3020BA. The original gaskets were either a very hard thick cardboard or an embossed metal piece, and the new gaskets are a really thick, soft cardboard.

The original exhaust manifold gaskets are sort of a metal/asbestos/metal sandwich with dimpled surfaces, and the new ones are the same stuff except that they have added a collar around the center opening.

The original valley cover gasket was a piece of thin paper, and the new one is a piece of thin Gortex -- black on one side, red on the other, but it doesn't seem to matter which way you install it; it's really flexible, it even comes all crumpled up in a bag.

I would like someone to tell me what's updated about the thermostat housing gaskets; they look like normal paper gaskets to me. They are black paper and kinda thin, while the older style is thicker red paper. The only other difference I can see is that the outside edge of the newer 3-bolt cover gasket lacks the bulge at one corner, so it can fit on in any of three positions.

The original coolant manifold gaskets were apparently very thin paper and later versions were really thick paper; the EBC 9634 gaskets are Gortex/metal sandwiches, and are pretty thin. There are 12 used on the engine, although because some are used under the coolant headers and others are used under blank-off plates they may be listed in catalogs as 8 needed in one place and 4 in another. Note that the steel blank-off plates tend to distort with stress and time, especially if they've been holding down the thick paper gaskets; prior to reinstalling, it'd be a good idea to run a flat file across the bottom to make the surface flat again.

The same gasket is used on both sides of the throttle body, between the air filter housing and the throttle body and between the throttle body and the intake manifold, so you need a total of four. The EBC 9635 gasket is a Gortex/metal sandwich and has 7 bolt holes in it; four in a rectangular pattern, two more at 10 and 4 o'clock for the hidden bolts that hold the throttle body to the intake manifold, and a single loop that can either point straight up or straight down depending on which way you flip it. This last feature serves no purpose on the '83, and can either be cut off or left in place to hang out the edge of the assembled joint.

Most of the new gaskets are only moderately expensive, but the cam cover gaskets are obscenely expensive. Apparently as a result, some of the mail order places continue to stock the old paper versions.

The new gaskets should be widely available. Be sure to check the part number or description of the gasket as some parts people will try to give you the old style to get rid of old stock.

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

Even using the new gaskets, Neal recommends the following procedure for the cam covers: "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.

"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!

"The absolute best cam cover gaskets are available from Worldpac, if you know a shop that buys from them, give them a try! They are thicker than the oem stuff and don't stick like the oem crap either."

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.

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."

Regarding sealants, Roger Homer says, "I use some stuff from Caterpillar (The engine variety, not the garden variety!). I'm not sure of it's official name/number but out here I just go into the local Caterpillar dealer and ask for a tin of Cat Red. This stuff isn't cheap, but it works well, it will seal the gasket joints but not weld itself like glue to either surface; if the gasket needs replacing later Cat Red virtually peels off both surfaces."


CAM COVER BOLTS: Regarding the cam cover gaskets, Michael Neal says "New bolts are also necessary. They use an 8mm head with a built in washer. Unfortunately these parts are only carried by the dealer." Note: 8mm is essentially the same as 5/16", so this isn't necessarily an example of metrification. The part number for the new bolts is FS-106251/J.

The replacement of the bolts may not be as much due to the excellence of the new bolts as to the lousiness of the old bolts. The original bolts have a "triangulated" thread that presumably helps it to drive into the aluminum housing, but probably is also very effective at boogering the aluminum threads up.

If you'd rather not pay Jaguar prices here and seek other sources for bolts, note that 7/16" hex heads will not do, you can't get a wrench on it; either 3/8" (or smaller) hex head, socket head (allen wrench drive) or Torx drive bolts will be necessary. And you might want to look at the access before you select bolt head styles, since you may want to retorque them a while after replacement. Of course, buying el cheapo grade-zilch bolts (like most slotted head screws) is not a good idea; not only will they rust pretty badly, they may not hold enough tension to prevent the cam cover gasket from leaking.

An alternative bolt that would work was found at a Home Depot in their "specialty fasteners" rack. It is called a "serrated flange bolt"; it has a 3/8" hex with a washer face, and a row of serrations around the bottom of that washer face. The biggest problem will be finding enough of them to do the job; often such racks in hardware stores only contain a half dozen or so.

Another alternative: this author bought a box of 1-1/4" "alloy steel" 1/4"-20 "socket head cap screws" from a local industrial fastener supplier -- less than $20 for a box of 100. These fasteners are jet black. Strength is not a problem, alloy steel cap screws are stronger than Grade-8.

The original bolts were 1" long, so replacing them with 1-1/4" bolts provides enough length for some washers under the heads (and perhaps for thicker gaskets, if you find something non-OEM). There's no problem with bolts being too long, since the end just comes out the back side of the flange on the tappet block. With these socket head cap screws, the author used split ring lock washers and flat washers.

As noted in the section on General Maintenance, flat washers are always recommended when a bolt head or nut sits on aluminum. This author found some very suitable flat washers on a bubble card in a Wal-Mart: they are size 12, also known as 3/16". If you ask for 1/4" flat washers, you get washers that fit so loosely on the screw that it looks like a socket head might pull through the hole! Also, the OD of the standard 1/4" washers are bigger than the flat area on the cam covers, so you'd have to cut them down to get them in. Conversely, these #12 washers fit perfectly on a 1/4" bolt and are the correct OD for the cam cover flats. Make sure you find cheap #12 washers; better quality ones might have closer tolerances and not fit a 1/4" bolt.

You can buy enough flat washers and lock washers to do this job for less than two bucks total.

Another type washer that will work on the cam covers is the 1/4" spiral groove washer used in a couple other places on the V12 -- if you can find a supply of them. These washers serve as both a flat washer and lock washer in one. Also, the 6mm wavy spring washers mentioned in the section on General Maintenance as a substitute for the spiral groove washers will work nicely.

As always, be sure to use anti-seize compound on the threads when assembling.


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 "The drain plug washer for the S3 XJ6 and XJ-S can be replaced with the transmission cooler line banjo bolt seal from an XJ40, EBC4896. This is a neoprene-lined washer that is reusable, life is about a year or two."


LEAKY O-RINGS: The O-rings available at your local parts store are probably as good as the Jaguar originals -- which is to say, not worth a damn. Whenever an O-ring is encountered during disassembly of the V12, it invariably is hard and brittle and has long since ceased sealing properly. It has been suggested that Viton O-rings would serve better, although you will need to visit a good industrial supply place to find them. They can be ordered in various colors, but basic Viton O-rings are black so they cannot be distinguished from regular O-rings on sight. The price is a giveaway, though; they cost several times as much. Andy Hutchinson reports: "Looked at my book today. It would seem the choice of "elastomers" (posh for rubber) is Nitrile, Flurocarbon or Flurosilicon. Viton is Flurocarbon. Excellent hot and chem resistant. Not so good cold. Flurosilicon is good at both ends but not very tough (fixed surfaces only). Nirtrile is a good all rounder and I suspect the standard material. Rubber, silicone, neoprene, etc. are dogs." As long as you're not building Space Shuttle solid rocket boosters, that lack of cold performance of Viton may be acceptable; on the Jag V12, it'd be preferable to leak only in freezing weather than to leak all the time!


LEAKY BANJO FITTINGS: The copper washers used to seal the banjo fittings at the back end of the tappet blocks are really thin, only about .010" thick. Each fitting requires two washers. If your local auto parts store has a rack of red cards titled "Help!", it probably has a package of sealing washers that are the correct diameter for these fittings but a lot thicker: part number 66272, labelled "Brake Hose Bolt Washer". It says they are ID 25/64" and OD 5/8".

However, Craig Sawyers pointed out that the alignment of the oil feed hole in the banjo bolt doesn't line up with the feed channel in the fitting as well as might be hoped -- see Figure 1. The fitting is about 13/32" thick, with the feed channel right in the middle, but the feed hole in the bolt is located only about 5/32" from the underside of the head -- and the thickness of the sealing washer between the bolt head and the fitting makes the alignment even worse (the drawing at left includes a 1/16" thick copper washer, and the two passages barely overlap). The fix is pretty easy, though. Using a Dremel or some such, provide a chamfered edge on the oil feed hole in the bolt in the direction of the threaded end only (it's already chamfered a little, just enlarge it). This may help the oil flow to the camshafts even if the original thickness washers are used.

Now that you're practiced at this modification, do the same thing to the banjo bolt at the top right of the radiator.

When tightening banjo bolts, be sure to hold the fitting still. Failure to do so will allow the turning of the bolt to twist the fitting and bend the tubes.


LEAKY OIL PRESSURE SENDER CONNECTIONS: The connection at the block at the rear center of the V is a larger banjo bolt. For this fitting, Help! number 66265, "Brake Hose Bolt Washers" are a perfect fit. They are described on the package as ID = 33/64", OD = 45/64". These same seals fit the bolts that hold the heat shields to the exhaust manifolds.

The seal on the oil pressure sending unit itself is not the same as the banjo fitting. The sending unit fitting is the same diameter as many common oil drain plugs, though, so it is easy to find a suitable seal in an auto parts store. Note, however, that if you're buying a new sending unit, it will usually come with a new sealing washer


LEAKY OIL PRESSURE SENDER: When searching for sources of oil leaks, don't overlook the oil pressure sending unit itself. The unit can fail internally and oil comes seeping out of the electrical connector, a sure sign of trouble since there isn't supposed to be any oil within the electrical components in this unit. The author's car had this problem, and the gauge was still working just fine. Only solution is to replace it. C46272 is the part number.

I'd like to be able to tell you what commonly available sending unit can be used for a substitute, but I can't. The Jaguar V12 uses a 100 psi oil pressure gauge while most other cars (including Jaguar 6-cylinders) use an 80 psi gauge. The threads on the bottom of the gauge are BSPP (see the section on the radiator drain plug), but of course you could buy a BSPP fitting and plumb a line to a remotely-mounted sensor -- or just opt to replace the entire pedestal. And we haven't even gotten into the sender's electrical characteristics. Your best option may be to shop around the mail order places for the correct part, since prices on this item seem to vary widely and it sometimes can be found quite reasonable.


LEAKY OIL PRESSURE SWITCH: The oil pressure switch, which operates the warning light, is right next to the oil pressure sender -- and is even more notorious for leaking oil out through the electrical connection. The only solution is to replace it, but that's not difficult because the thread is standard and there are lots of cars that use very similar pressure switches. David Johnson says, "I screwed one from a Chevy in. The new one was a two wire type, so I simply connected one side to ground and it works fine."


OIL LEAKS AT FILTER HEAD ASSEMBLY: Peter Smith says "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 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 re-routed 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 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: The battery and starter must be in good condition. All of the spark plugs should be removed. Power to the ignition system should be disconnected, since an electronic ignition system may be damaged trying to fire with the spark plugs disconnected. And the throttle should be held at least part way open, usually by jamming something in the linkage. 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. 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 usually has to be removed to get at the front plugs, you will probably 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 US-spec pre-H.E. engine, the readings typically will be about 130-150 psi. The US-spec 5.3 liter H.E. engine has 11.5:1 compression, and will read about 200-220 psi. Note that readings will be lower at high elevations.

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 psig) 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 V12, 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. Also, just in case there's a leak in a head gasket, the radiator cap should be removed to prevent pressure buildup in the cooling system.

Kyle Chatman points out that if the leakdown test finds excessive leakage in a cylinder, it might be possible to determine whether the leakage is from the rings, the exhaust valve, or the intake valve by listening closely at the oil filler cap, the air intakes, or the exhaust pipe outlets. And a bad head gasket might cause bubbles in the coolant (especially if it's the center cap that was removed) or other motion in the coolant level.

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 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 a mechanic is using the same leakdown tester at the same pressure all the time, he 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 $60 to $70. In a pinch you could tee into the small hose on the center fill pipe and apply pressure.


CAM COVER WORK: If you need to get down to the cam covers or beyond, Victor Naumann sends this awesome tip: Remove the PCV crossover manifold, fuel rail and injectors, air injection manifolds, both fuel pressure regulators, the ignition amplifier, the intake manifold crossover pipe, both butterfly housings, and both intake manifolds as one piece. Be sure to disconnect the butterfly return springs before lifting.


CAM COVERS OFF?: If you remove the cam covers off for any reason that is not intended to include further disassembly of the engine, it cannot be reiterated too many times that every bolt, nut, tool, or whatever that is in this vicinity should have a string tied to it with the other end tied to your finger. If a metal part falls down into the timing cover while you're fiddling around, see the section on timing cover removal. Peter Smith suggests "I shove a big rag down the timing cover on each side to catch the bolts if they fall. I find this to be a nerve racking part of the job -- if the damned things fall in it can really test your sense of humour!"

The repair manuals provide complete instructions for timing chain disengagement and camshaft removal, except they neglect to remind you that you might want to measure the valve clearances before disconnecting the timing chain and removing the cams. The assembly must be together to make the measurements, so measuring before disassembly will save you having to slap it back together to measure it later. Of course, if you plan on reseating valves and the like, the measurements won't do you any good anyway.


MANIFOLD CROSSOVER PIPE HOSES: On the author's '83, the intake manifold crossover pipe is connected to the manifolds with a short, straight piece of 1" hose at each side. However, sometime before '89, the assembly was changed so that pieces of hose with 45 bends are required. If you have the earlier straight hoses and need to replace them, it's obviously pretty easy to find pieces of 1" hose. As for the later parts, Jeff Elmore says, "The dealer quoted me $22 apiece for these three inch long, 7/8-1" diam hoses with a 45 degree bend in it. Bennett Auto Supply had a Goodyear coolant bypass hose that fit perfectly for $2.62 apiece. Part number #gyy 63064."

Whatever you fit, note that the vacuum inside these parts is considerable, and long unsupported sections of rubber hose will be sucked flat. With the earlier design with straight hoses, it appears to be sufficient to merely be sure to insert the hoses far enough onto the fittings that there is only a short area of hose that doesn't have fittings within it. If you must have longer sections, you may need to insert a piece of wire coiled like a spring to hold the hose round, or perhaps just a short section of tubing.


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

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 -- see the section on ignition timing.

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."

Dale Knaus says, "To remove the nut on the end of the crank I used what we call a "slug wrench". It is a box end wrench made extra heavy with a striking pad on the other end. It is made to hit with a hammer to tighten and remove nuts. By paying careful attention to how much impact it took to break loose the nut, I had some idea how hard to hit it to tighten the nut back at reassembly. I would have much preferred to use a torque wrench, but couldn't figure out how to keep the motor from turning over. I tried not to overtighten the nut, didn't want to strip it. Used lock-tight on it to help keep it on there if it isn't torqued enough. If I ever need to put in a front seal, I'll use the slug wrench again. I borrowed the tool from the industrial plant where I work, they are probably available from industrial tool supply companies."

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


CRANKSHAFT PULLEY -- WOODRUFF KEY PROBLEMS: Paul Konitshek and Michael Neal report that the woodruff keys that aligns 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."

The other problem is a key that won't come out, notably on the key on the crank itself. Suggestions include using a pair of angle cutters to grab it and walk it upwards, and using a suitable chisel to cut under the key to pry it out. The suitable chisel needs to be a hair narrower than the key, and can be made from old lathe bits or "cut nails". Cut nails are made from flat stock, giving them a sort of trapezoidal shape, and are really hard for pounding into masonry. Greg Guillaume: "Here's what I did: get a 1" chisel, lay it on the crank, perpendicular to the crank, up against the key. Then whack away with a hammer on the opposite side of the chisel. The shape of the chisel is just right so it bites into the key, the 1" width hangs over the end of the crank, and you get a lot of room to swing the hammer. Of course, the chisel is a little beat up, but it worked great."


CRANKSHAFT PULLEY -- SPLIT CONE PROBLEMS: Dan Jensen says, "The split cone was broken in three places. Rather than pay $$ for a replacement, I just stuck it back into the damper/pulley with Hylomar sealant and gently replaced it. It centered properly and has worked great for 35K miles."


FRONT OIL SEAL REPLACEMENT: Peter Cohen points out that the Jaguar repair manual's procedure for replacing the front oil seal involves removing the radiator -- which, in turn, supposedly requires depressurizing the A/C freon circuit. Boy, I hope you read this first! Depressurizing the freon circuit is totally unnecessary to get the radiator out, and if you don't mind working in tight quarters, taking the radiator out is unnecessary to change the front oil seal. Matthias Fouquet-Lapar says, "I've done this in my garage without pulling the radiator. Once all the belt-driven hardware is removed, there is enough space. I did not even take out the fan shroud." Brian Sherwood says, "I replaced mine without pulling the radiator -- not very convenient, but possible. The most difficult parts were: 1. removing the old seal (finally had to prick a small hole in it, and screwed in a sheet metal screw to pull on), and 2. getting the pulley bolts thru the lock plate, pulley, and into the crank damper -- can't see these at all, have to do by feel."

When you buy the front seal from Jaguar, you get the seal and the spacer sleeve it rides on in one box; this may be a recent development, apparently a new part number has been issued. Matthias Fouquet-Lapar says, "The new part at least includes the spacer. The part number is JLM 10613." However, if you buy a generic seal somewhere else (or maybe older stock from Jaguar), you'll probably get just the seal. You can look at the condition of your sleeve and see if you think this will cause a problem. Peter Smith says, "If the spacer appears worn it can simply be reversed on refitting because the seal does not ride at the half way point. The new seal will then ride on an unworn part of the spacer." Whatever, you will want to take the sleeve out, because the proper order of assembly is to install the seal and then install the sleeve.

You might also consider putting some sealant between the crank and the spacer prior to installation to absolutely prevent oil from travelling between the crank and the sleeve and leaking out the splits in the split cone under the pulley. There are no reports of leaks this way, but if it did leak people would think it was the front seal, so who knows? Maybe it's a common leak!

Cohen adds, "Oh, and by the way, although the old spacer slid off, the new one had to be driven on. The dealer tells me they are all like that, and that they loosen up after time..." Who knows, maybe the new seal comes with a coating on the inside to seal it, the sealant goes away with time, and that's why Jaguars leak!

Also of note, illustrations in the repair manual indicate that the sleeve has a keyway, but according to Alex Dorne they lie; "The sleeve is not keyed."


TIMING CHAIN TENSIONER ACCESS COVER: Before going any farther, please read the warning about having the cam covers off: the same warning applies here.

The access to the timing chain tensioner latch is via an opening on the timing chain cover, forward of the right bank and just above the support for the belt-driven fan. 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 has been 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.

If you have access to a lathe, it shouldn't be too difficult to make an aluminum plug for this hole with provision for fitting an O-ring for sealing.


TIMING CHAIN TENSIONER: There are few design features of the Jaguar V12 as poorly conceived as the material the arch of the timing chain tensioner is made of. If you manage, on your first try, to retract the tensioner and reengage it successfully without breaking this arch, you should consider yourself lucky. The arch 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.

Other engines have arched timing chain tensioners in which the arch itself is made of spring steel. It would seem a simple matter to design a replacement arch for the Jaguar V12 tensioner made of spring steel, thereby eliminating the fracture problems permanently; if noise or wear is a concern, the spring steel arch could be faced with Teflon or some such. However, despite more than two decades of trouble with this piece of junk, apparently neither Jaguar nor any aftermarket companies have opted to offer an improved part.

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 near the pinned end 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 in mid-air.

Before proceeding, please reread the warning on having the cam covers off.

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, underneath the cam sprocket, and hooks onto a hole in the steel foot at the top end of the tensioner; this tool is for pulling the tensioner back to the disengaged position, and has a lever handle shaped to rest against the top of the sprocket. The other tool is inserted through an access hole in the front of the timing cover and is used to manipulate the rocking latch. The rocking latch has a slot in it, 3/16" wide by a little over 1/2" long and roughly parallel to the chain line, 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, but you'll need to trim the hook as shown in Figure 2 in order for it to fit the hole in the tensioner properly. Adding a lever that rests on top of the sprocket isn't too hard, you can even make it out of wood; just drill a 1/2" hole near the center of a 1" x 2" board about a foot long, insert the battery hold-down bolt through it, and put a fender washer and a wing nut on the end. The hole needs to be about 1/2" to allow the battery hold-down bolt to tilt relative to the board.

Alternatively, 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 if you can get it in there. 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. You should note, however, that while these items may get the job done, none of them are likely to work smoothly enough for you to get a good idea of what you are doing to that tensioner by feel.

You can easily make a more suitable tool: Buy a piece of strip steel 1/8" thick x 1/2" wide (commonly available at hardware stores), and cut off a piece about 7" long. Then, about 2" from one end, make a sharp bend of something less than 90 degrees -- see Figure 2. Then cut away one side of the tool -- the side that will be pointed toward the cam cover opening -- about 3/16" as shown. This is because as you retract the tensioner, the latch moves upward with it and this side of the tool will contact the edge of the access hole. This contact confuses the "feel" and can leave you wondering if the tensioner is fully retracted or not.

Of course, you could avoid having to cut away the side of the lever by simply making it out of 3/8" wide strip steel to begin with. However, this is not recommended. The portion of the rocking latch above the slot is not very thick, so having a lever a full 1/2" wide to insert in the slot ensures that the tool contacts the rocking latch near the ends of the slot. If a narrower tool is used, applying torque to the lever can cause one edge of the tool to push up on this thin portion of the rocking latch near the center of the span rather than near the edge, greatly increasing the chances of actually breaking the rocking latch. Breaking this portion off doesn't really affect the normal operation of the latch, but it will make it even harder to release, and if that broken portion falls down into the crankcase you're gonna be upset about it.

The other feature shown in Figure 2 is a small pin sticking 1/8" up from the surface of the lever. The purpose of this little pin is to prevent insertion of the tool farther than 1/4" into the rocking latch, where it may get involved with other parts. A tiny roll pin could be used here, or perhaps a small screw. You can even omit this feature, if you are careful not to jam that lever in farther than it needs to go.

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 CCW 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 CCW -- unless, of course, the tensioner is already broken.

Now, to actually retract the tensioner: First, rock the latch CCW and hold it rocked; it doesn't need to be held hard CCW, just so that it is prevented from returning to the CW 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 CCW direction. While holding the latch firmly in this full CCW 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.

When it comes time to reengage 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, below). Use the special tools to gradually release the tensioner into its normal position. Pull on the tensioner while rocking the latch in the CW 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.

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, your only option may be to use the latching mechanism as intended and hope for the best.


TIMING COVER REMOVAL: 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.

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 (with duct tape) in a raised position while the cover is being removed. Once the cover is off, they can be removed.

4. Remove the retaining bolts holding the timing cover to the block.

5. 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 this section if you wish to remove the sandwich plate entirely.

6. REASSEMBLY: 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.

7. Before reassembly, carefully trim the timing cover gaskets flush with the upper corner of the timing cover.

8. 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.

9. Neal provides this tip for getting the timing cover back in between the heads and sandwich plate: "On reassembly I use sheets of .003" shim stock on the upper surface of the sandwich plate gasket and the underside of the front of the head gaskets. 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 head gaskets are...very prone to wrinkling if you don't use the shim stock pieces to slide the cover back in."

10. When threading the new timing cover-to-head 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.

11. 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.

Note that if the engine is still in the car but the heads are off for some other reason, the timing cover should be removable without too much additional trouble, basically following the rest of the steps in the repair manual and skipping step 5 above. Hence, you might consider going ahead with removing it, replacing the chain and tensioner, checking out the oil pump, etc., depending on the age and wear on the engine. You might also consider installing the longer studs as described in step 6 above while you're there.


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.

Elsewhere I describe 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 were 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 discourage you from assuming the position of these plates is unimportant, skipping important steps, and causing yourself a great deal of heartache down the road.


TIMING CHAIN REPLACEMENT: The timing chain in the Jaguar V12 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 than 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."

Supposedly, it may be possible to replace the chain itself by removing only the right side cam cover and without bothering the timing cover at all. Retract the tensioner, then break the chain on the top of the cam sprocket and connect the new chain to the end of the old one. Have someone turn the crankshaft slowly while you feed the new chain in and the old chain out, being sure to keep the cam sprocket engaged at all times. When you reach the other end of the old chain, disconnect it and connect the new chain back to itself. You may wish to ask if the new chain has a master link prior to buying it to make this job easier; supposedly, some do and some don't.


CAMSHAFT SPROCKET REMOVAL: The V12 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 grooves for a clip to secure the sprocket on the bracket.

The clip, also known as tool JD.40, can obviously be improvised with sheet metal or even a normal 1/4" E-clip, perhaps with a 5/16" flat washer behind it. Note: The size of an E-clip is the size of the shaft it typically fits, not the diameter at the bottom of the groove it fits in. The diameter at the bottom of an E-clip groove on a 1/4" shaft is about 3/16", so that's the ID of a 1/4" E-clip. The stubs on the front of the cam sprockets at 5/16", but they have exceptionally deep grooves and the OD at the bottom of the groove is about 3/16", so 1/4" is the correct E-clip size.


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 $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.



Engine Maintenance is Continued...


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