Jaguar XJ-S. Service manual — part 36

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wheel, for example) you’re still gonna be in a pickle putting the rebuilt distributor back on without tearing it back apart
or turning the crank while the distributor is out.

If you turn the crankshaft while the distributor is out, you face additional problems. The distributor turns once every
time the crankshaft turns twice, and therefore the distributor must not only be lined up facing 1A while the engine is at
10° Before Top Dead Center (BTDC) but it must be on the correct stroke. If not, the spark plugs will fire at the end of
the exhaust stroke instead of the compression stroke, and the motor will not run.

To get the setting right, cylinder 1A must be on the compression stroke when the distributor is installed pointing to 1A
on the cap. If you know in advance you may be turning the engine, it is easy enough to avoid problems. While the
distributor cap is off and the rotor is pointing at 1A and the crankshaft is at 10° BTDC, remove the oil filler cap. Reach
beyond the front edge of the chain and mark the camshaft gear itself (the camshaft gear turns at the same rate as the
distributor). You can use a dab of paint, or stake it, or whatever will give you a clear indication.

You might also want to mark the position of the base of the distributor, since it mounts on slotted holes. Ideally, the
base should be mounted so the correct timing is near the center of the range of the eccentric adjuster, but to begin with
it will be easier to put it back where it came from. Peter Smith: “I find that using typist’s white out to paint across
components can be helpful. It can be applied over slightly greasy surfaces and if precise alignment is necessary I can
draw on it with a biro.”

You can insert an allen wrench through the openings in the distributor and undo three screws and remove the distributor
as a unit. However, for the purposes of doing the marking mentioned above, it may be preferable to proceed with the
disassembly described below with the distributor still on the engine until you’ve removed enough parts to be able to
mark the bottom of the housing on the inside.

DISTRIBUTOR DISASSEMBLY: Remove the rotor arm; see page 125.

Remove the EFI trigger board or anti-flash shield (whichever). The biggest problem with removing the anti-flash
shield will be dropping the tiny screws and washers, but the trigger board causes more trouble. It is mounted with four
tiny plastic screws, and Jan Wikström reports that the screws get stuck to the metal; “On my own experience of three
distributors, you can expect to get two out intact. If you’re very careful.” He also reports that he has used metal screws
in a pinch with no apparent problems. When installing the plastic screws, maybe it would be a good idea to use anti-
seize compound, even though it looks silly on tiny plastic screws.

Richard Dowling dealt with the trigger board screws differently: “I retapped the holes to M4 (about 2 times stronger)
and fitted bigger nylon screws.”

Next, remove whatever is used to trigger the ignition; on 1982-89 cars, you need to remove a C-clip, then slide off a
wavy washer, then pry out a U-shaped pin. Finally, you need to slide off the iron star-shaped inductor rotor, being
careful not to damage it or deform the points. Even more importantly, don’t just pull upward on a sticky star rotor,
because you may stretch the springs in the centrifugal advance mechanism underneath. Here’s a method that seems to
work: Lift gently on the star rotor a little bit and insert the claw of a claw hammer under the star rotor. Rest the head of
the hammer on the edge of the distributor housing, but do not pry. While holding the star rotor in its slightly elevated
position with the claw hammer, tap downward on the center of the rotor carrier shaft with a plastic-surfaced hammer.
Once the end of the rotor carrier shaft is flush with the surface of the star rotor, if it still won’t simply slide off you can
position a small socket with an OD slightly smaller than the rotor carrier shaft on top and continue tapping.

On the pre-1982 cars, a plastic disk with 12 ferrite inserts was used; according to Jan Wikström, “Its hub is about an
inch long (estimated; I’ve never seen an intact one) and all beneath the disk. It’s a tight fit on the spindle and in its
keyway. And the disk, which is all you have to apply force to, is about 3/16 in thick near the hub. On an old car like
mine, the only way to get the disk out would be by breaking it up.”

Fortunately, John Nuttall found a better way: “I discovered a technique for removing the circular plastic timing rotor
which, according to Jan W in your book, often breaks under extraction. The idea is to undo the three screws which
hold the movable part of the distributor body to the base. This can be done with the rotor in place. These screws have
springs on them to allow the body to rotate when the vernier is turned. It is then possible to push upwards on the rotor

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with the body with the force being applied uniformly very close to the central shaft of the rotor - much better than
pulling at the edge.”

Unfortunately, Wikström counters: “It’s better than fingers, although it still bears on the thin part of the disk outside
the hub. But sure, it’s worth trying before you break the disk up. One hitch: If you don’t have the distributor with the
little screw inside the top of the shaft, lifting the micro housing (charming name, isn’t it?) will pull the centrifugal
advance mechanism apart without shifting the disk.” And stretch your advance springs beyond recognition. If you
can’t rely on the retainer to hold the rotor carrier shaft still, you must press down on the center shaft with your thumbs
while pulling up on the housing to get the disk off. Maybe some method involving tapping with a plastic-faced
hammer will work here, too.

Whichever distributor you have, you must remove the three screws with springs and lift off the movable portion of the
base to gain access to the centrifugal mechanism below. You could leave the pickup assembly in place, but on the
1982-89 it’s in the way for getting to one of the screws with springs; since it’s only two Pozidriv screws to remove the
pickup assembly, that’s the easy solution. Of course, it’s a good idea to inspect the vacuum advance mechanism as well
as the pickup module while you’re there.

Note how the centrifugal weights and springs are installed. Being careful not to stretch them, disconnect the springs
from the pivot posts for the centrifugal weights; Carlos Artal says, “Use a piece of strong, thin string (such as fishing
line, etc. -- I used dental floss) to take away the springs without damaging them or overextending them. It works for
mounting them too. Just get one extreme, and pull slightly outwards and up.” You don’t have to disconnect the springs
from the posts on the rotor carrier base plate if you don’t want to; you can just let them dangle. Yes, the two springs are
different, but it doesn’t matter which one goes on which weight.

Remove the felt from the top of the rotor carrier (if there is any) and observe the retainer underneath. This is a possible
cause of trouble. The early cars had a screw there, but on later cars there’s a nylon clip instead. The nylon clip is
usually brittle and cracked, sometimes allowing the rotor carrier to rise on the distributor shaft and possibly causing
interference damage down in the advance mechanism. If you don’t have a screw, the procedure for removing the rotor
carrier is to yank, which usually results in breaking the nylon clip.

Normally the rotor carrier shaft should slide off the distributor shaft at this point, but if it is seized some Liquid Wrench
or other measures may be called for. Please try not to bend the distributor shaft -- it is remarkably thin within the rotor
carrier. And don’t grab the rotor carrier shaft with pliers or vice grips -- the metal isn’t that hard, you’ll booger up the
surface, and then it will be difficult to get the plastic wheel or star wheel back on. Once apart, clean all the crud off the
bearing surfaces. Decide for yourself whether Bywater or I am right, whether it seized due to lack of lubrication (dry)
or a lousy lubricant (gummed or varnished).

There are photos of some of the parts within the distributor at:

http://www.jag-lovers.org/xj-s/book/Distributor.html

DISTRIBUTOR SERVICE KIT: A distributor service kit, part number DZB105, is available; it is often called an
“anti-flash shield kit” since the anti-flash shield is the most obvious part in the bag. The kit contains parts usable on all
pre-Marelli distributors. Stefan Schulz points out: “It's a Lucas part number rather than a Jaguar one. My friendly not-
so-local Jaguar parts man couldn't find it on his system.”

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The mail order catalogs may not list what parts are supplied in this kit, so the list is provided here:

Clear plastic anti-flash shield (used on 1982-89 only)

Screws and washers for anti-flash shield (4 ea)

Ignition pickup mounting screws (2 ea - used on 1982-89 only)

Distributor cap gasket

U-pin for reluctor positioning (used on 1982-89 only)

Reluctor retaining clip and wavy spring washer

Replacement carbon contact for distributor cap, with spring

O-ring for distributor-to-engine joint

Nylon rotor retaining clip (see note under DISTRIBUTOR DISASSEMBLY above)

It may not really be necessary to obtain this kit to perform a distributor overhaul. The O-ring can easily be purchased
locally, and you’d be well advised to find a Viton one anyway. The rotor retaining clip, while not likely to survive
disassembly, can be replaced with a couple of small washers and a tiny O-ring -- see CENTRIFUGAL ADVANCE
REASSEMBLY below. The existing anti-flash shield, screws, cap gasket, U-pin, retaining clip, wavy washer, and
carbon contact may all be reusable -- and if not, screws and washers can be purchased separately, a gasket can be
purchased separately from Jaguar (DAC4063) or cut from gasket stock, and a carbon contact can be pilfered from some
other type of distributor cap.

In fact, the only part of this kit you’re likely to really need is the anti-flash shield itself since the old one may be brittle
and cracking. You could try buying it separately from Jaguar; it’s part number AEU1722. Or you could try fabbing a
flat disc from clear plastic and installing it with four long nylon screws and some nylon nuts to support it at the same
level as the top of the original shield; you might drill the four holes in the housing out and tap them larger to permit
using stouter nylon screws. You could try fabbing a shield from the bottom of a plastic container of some sort, again
finding a way to hold it in place without creating an electrical path to ground. Finally, you could just omit the anti-flash
shield entirely, since it’s plausible that it’s entire purpose in existence was to provide a purpose for the four screw holes
that were originally intended to hold the trigger board on D Jetronic cars.

DISTRIBUTOR SHAFT SEAL: The Jaguar V12 distributor has had two common problems, centrifugal advance
seizing and cracking distributor caps. Both of these problems have been attributed to crankcase vapors entering the
distributor between the shaft and the housing. Supposedly the vapors condense into the type of varnish found inside
engines, seizing the advance mechanism. Vapors collecting within the cap are ignited by the arcing of the distributor
and cause an explosion which cracks the cap.

Both causes are in question. Hard deposits that seize the advance may very well be the original lubricant exposed to too
much heat. And Jaguar’s reported reason for venting the later distributor caps was to deal with high temperatures that
caused the caps to crack, although clearly the vent system could also remove collecting vapors. It is noteworthy that the
later, vented distributors are still prone to advance mechanism seizing, and the still later Marelli distributors are vented
even though they have no advance mechanisms to seize. And the real source of the explosive vapors is the incompetent
mechanic who has addressed a seized centrifugal advance by spraying WD-40 down the center of the shaft, which spun
out and was ignited on startup and blew the cap apart.

There is a seal between the shaft and the distributor housing, but it gets hard and brittle, probably due to the heat in this
area. If the distributor is being worked on, it might be a good idea to replace this seal. Note that removing the
distributor drive gear retaining pin requires some grinding, and reinstalling the pin requires a tack weld to hold it in
place. There’s a bearing in there, too, you might wanna renew it while you’re there.

RATTLY PARTS: Richard Chapman had another problem: “The pressed connection between the rotor shaft and plate
where the springs connect was loose. I brazed it very carefully and that made the timing reading stable rather than
flickering.” This is not a rare occurrence; be sure to check your rotor carrier for looseness before reassembly.

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THINGY: Highly technical term referring to a specially-shaped plastic thrust washer at the bottom of the rotor carrier
shaft, just below the centrifugal advance weights. It has ears on it that appear to provide an inner stop for the
centrifugal weights, apparently to reduce noise but effectively limiting how retarded the timing moves at idle. It’s also
a British non-metallic part, so it may be cracked or broken. Note: If you have the early distributor held together with a
screw under the rotor instead of the nylon clip, you don’t have a thingy and don’t need one.

If you’re lucky enough to have an intact thingy, you need to take care to reinstall it properly during reassembly. If you
just look at it and line up the notches with the “wings” on the cam plate on the bottom of the rotor carrier shaft, there’s a
better than even chance you will have installed it wrong. There is a pair of pins on the thingy that hold it in position
relative to the cam plate, and the correct position of these pins is shown in Figure 9. Note that for clarity the thingy
itself is not shown, only its pins.

RIGHT

WRONG

Figure 9 - Locating the Pins on the "Thingy"

If your thingy is toast, bad news: This part is apparently unobtainable. It’s not included in the DZB105 kit. One
frustrated owner reported: “I phoned Lucas Aftermarket Operations, Parts and Service (note: See page 702).
Apparently, they have routine service parts which are readily available at most dealers, other service parts which
they can provide part numbers for and which are often available, and then there are non-service parts which of
course the thingy and the seal fall under. The parts did not show up on his drawings although he did have DZB105.
He could see the shaft bearings in the drawing, but no seal and no plastic thingy. I asked what happens to parts that
are not on their drawings anymore. I was advised that once it is not profitable to sell replacement parts, they are
removed from the aftermarket listing and so, to Lucas Aftermarket the part numbers are no longer available. He
told me that the part numbers could only be obtained from the factory drawings once they were declared non-service
parts. He also advised that they factory would not talk to me about this because that is what Lucas Aftermarket is
for. So, Lucas Aftermarket is apparently the only information source Lucas has for part numbers and they do not
have these parts listed anymore.”

You’re screwed. The only option -- and it’s a perfectly workable one -- is to install a generic 5/16” ID flat thrust
washer in place of this thingy. Val Danilov adds “I wouldnt use any washer there larger than 0.5in OD, as it may
interfere with the weights.” The thrust washer also needs to be at least .060” thick, although if thinner you could
merely stack two in there; the ideal thickness is around .078”, but you could probably install anything up to about
.120” without any problem. The loss of the inner stops for the centrifugal weights will evidently allow the timing to