Jaguar XJ-S. Manual — part 24

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edge of the crank damper. As a result, such a slippage between the inner and outer portions of the damper would have
made correct timing impossible. Most of the cars with the later Bosch 115-amp alternators and ribbed belts (see page
571) also have Marelli ignition, and the timing is not adjustable -- but is established by a pickup at the front damper.
This pickup senses trigger points attached to the inside portion of the damper, so they are unaffected by slipping of the
outer ring and the engine runs normally.

It’s easy to blame these damper failures on the higher loads imposed by the 115-amp alternator or even on some change
in build quality between the V-belt dampers and the multi-groove dampers, but there is one more possible cause for
these failures. As described on page 571, there is a flaw in multi-groove pulley design that results in them slipping and
squealing even when the belt is tight. Obviously, most mechanics will address a squealing problem by tightening the
belt -- and since that won’t fix this problem, they may respond by tightening the bejeezus out of it. An overtightened
belt applies a considerable radial load on the rubber portion of that damper, and this load cycles around the damper as
the crank rotates. It would be logical to assume that such a cyclic load could rip that rubber loose from the metal in a
fairly short while. All owners of Bosch alternators are advised to have that alternator pulley modified at the next
convenient opportunity, and then adjust the belt to a reasonable state of tension.

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
(see page 197), 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.”

Tom Amlie had trouble getting the new seal installed in tight quarters. “If I kept trying to do it like the books said, I
would still be at it. Book says to tap the new seal in. Not possible. Go to Home Depot or similar and get a PVC drain
pipe fitting (reducer) to fit the seal. Carve on it until it works. Then use that huge bolt that holds the pulley/damper to
push it in. Works like a charm.”

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 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 along this path, but if it did leak people would think it was the front seal, so who knows? Maybe it’s a
common leak!

Cohen adds, “When I did my front seal 7 years ago, the collar that came with the seal had to be tapped into place, even
though the old one slid right off. The dealer assured me that that's normal, they loosen up with time. This is not true. I
had to drive the collar off after 7 years and 70,000 miles. It's a good thing the timing cover was off, because I don't
know if I could have gotten a grip on it from the front.” Who knows, maybe Jaguar figured out how the oil was leaking
out so new seals come with a coating on the inside of the sleeve to seal it.

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.”

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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 an unevenly-spaced series of notches rather
than evenly-spaced because an uneven spacing eliminates whine. For the same reason, cooling fans have unequally
spaced blades and tires have unequally spaced tread patterns.

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

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

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. See the info on seal replacement on page 91.

If you do need to remove the timing cover, Section 12.65.01 of the ROM 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 -- see page 88.

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

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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 page 96 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 Haynes manual, Chapter 1, Section 42, Step 5, suggests using quick-drying paint to
mark their locations before removal. Craig Sawyers says, “Nice idea, but no dice. Have a look at the bare block and
you will see that the dampers fit onto raised bosses. There is no accessible metal to either paint or scribe a line on to
show the original position of the dampers.”

If you move them, the use of an elaborate (and undoubtedly expensive) special tool JD.38 is required to properly
position them. Advice: Don’t move 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.

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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.

On page 92 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.”

Once you’ve decided to replace the chain, the next question is whether to pay Jaguar prices or simply drop into an
industrial supply store and buy generic chain. You don’t want cheap chain, that’s for sure -- but most industrial supply
stores actually carry really good chain, probably as good or better than the chain sold through Jaguar. Many of these
stores will also happily explain to you why you want a good chain rather than a cheap one and perhaps even show you
examples of each.

When ordering a chain from some parts houses, the chain they offer is a length of generic industrial chain and a master
link to put the ends together. This leads many owners to question whether they want to do this or pay for the Jaguar
part which is a loop without a master. Those aren’t the only choices, actually; if you think a master link is a problem,
that same industrial supply store will offer to make the loop for you. They have the special tool on hand to properly roll
the end of a pin over to make the chain into an uninterrupted loop. And this will still save you perhaps 2/3 of the cost
of the Jaguar part. Remember, Jaguar isn’t fabricating custom chain for this application; the chain they sell was
purchased from an industrial supplier and made into loops.