Jaguar XJ-S. Manual - part 18

 
 

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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 4.  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 4 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. 

Bob Gallivan reports:  “The drum brake adjusting spoon is the right way to go, just under 1/2" wide, cheap & easy to 
drill a hole in for the roll pin stop.” 

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 a bit 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 on page 92).  Use the special tools to gradually release the tensioner into its normal position.  Pull on the 
tensioner to remove tension from the latch itself, and use the rocking tool to hold the latch near the center of a rock -- 
not fully CCW nor fully CW, sorta halfway in the middle.  While holding the latch mid-rock (and perhaps rocking it 

 
 

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back and forth a little), 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. 

 

TIMING CHAIN TENSIONER -- 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.  Even if 
it doesn’t break immediately, this stress may start small cracks that cause the tensioner to break shortly after 
reassembly. 

Simple solution:  Don’t retract the tensioner!  When it comes time to take the sprockets off the camshafts, just do so and 
set them on the holders -- allowing the tensioner to take up the slack in the chain.  During reassembly, simply use the 
latch release tool to hold the latch CCW as you pull the sprockets back up into position on the camshafts.  This method 
has been tried and works fine. 

All this means you will only need one of the two tools shown in Figure 4 -- and since you won’t ever get near the 
fully-retracted position, you won’t need to grind the side off the lever. 

It is of utmost importance that the latch on the tensioner be rocked CCW in order to allow the tensioner to release the 
tension it took up during disassembly.  In fact, it’d probably be a good idea to rock that latch on at least two separate 
occasions during reassembly.  First, obviously, it should be rocked during the reinstallation of each sprocket.  Finally, 
after the distributor has been reinstalled and there’s no more need to leave the crank in a particular position, the latch 
should be held in the CCW position as the crank is turned by hand through a complete turn or two. 

Failing to do this reportedly results in a whirring sound from up front when the engine is started.  Amazingly, it 
apparently does not destroy the tensioner; just realize what you forgot, go back and rock that latch once, it goes “pop” 
as the excessive tension on the chain is released, and all is well.  Craig Sawyers says, “Precisely what happened to me a 
year ago.  Saga was that during replacement of skinny washers at oil feed, I stripped the thread in the back to the tappet 
block.  Tore it off to get an insert put in, and when I got the thing back together there was a worrying whirring noise 
from the front of the engine related to the revs.  Aargh.  But - pulled the rubber plug and stuck a screwdriver in (using a 
pice of mirror and a flashlight to see exactly what was going on) and "pop" went the tensioner.  All was A-OK after 
that.  Now during the reassembly process I could've sworn that I'd released it -but obviously not enough.” 

 

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 are 5/16” in diameter, 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. 

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

 

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. 

 
 

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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. 

It is very important that you check the condition of the damper before relying upon it to set camshaft timing -- 
especially if it’s a later car with the Bosch alternator, which tend to shear the damper as mentioned on page 90.  If the 
damper shears while running it may squeal or affect battery charging but otherwise isn’t too serious, but if you rely on 
the marks to time the camshafts and the marks are wrong due to a sheared damper you may crunch pistons against 
valves when you hit the starter. 

 

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

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

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

The upper row of fasteners on the tappet block are different, though.  If the car is a pre-‘84, they are a coarse thread 
rather than a fine thread, so the torque values aren’t necessarily equal.  The objective should be to achieve the same bolt 
tension, but the difference in threads means it will take a different torque to achieve the same tension.  Judging from 
other similar applications, it appears that coarse thread fasteners should be tightened to a slightly higher torque than fine 
thread, so torquing these to perhaps 12-15 lbf.ft would be in order. 

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

Another option is to check for bits for electric screwdrivers.  These bits are 1/4” hex shafts about 2” long to fit in the 
chuck of an electric screwdriver or drill, and there are all kinds of tips to drive almost anything.  If you can find a bit 

 
 

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with a 7/32” hex tip on it, you can put it into the head of the bolt and drive it with a torque wrench connected to a 1/4” 
socket.  Unfortunately, finding this particular type bit may prove a little difficult. 

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

From ’84 on, the socket head cap screws are metric and require a 6mm Allen wrench.  It might actually be easier to 
find a 6mm hex driver that will attach to a torque wrench than a 7/32”, but if not the above ideas will work -- just 
change the sizes accordingly.    Sam Lysinger reports that you can get a 6mm Allen drive socket from Sears or Snap-
On, either individually or in sets. 

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

Good luck torquing the bearing cap nuts to 9 lbf.ft. with a 150 lbf.ft. torque wrench, which is the only thing available at 
most auto parts stores.  J. C. Whitney (page 691) offers a torque wrench with a 0-600 in.-lbs. (0-691 cm-kgs.) range, 
catalog number 15xx01148.  Lysinger reports that NAPA offers four different models of torque wrenches with a 20-
150 in-lbs. range ranging from cheap junk to premium, and that Sears also carrys one. 

 

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

So, how do we seal it?  The ©1975 ROM, sections 12.13.29 and 12.13.30, says “Smear mating surfaces of tappet block 
and cylinder head with Hylomar.”  Michael Neal says,  “Hylomar is a sealant that does not harden over time.  It is still 
readily available and is blue in color.  It is commonly used to seal the liners into the V12 motor and the cam towers to 
the heads.  I’ve stopped using it to seal the cam towers because a good blast of carb cleaner or an aggressive steam 
cleaning can dislodge it and cause an oil leak that leaks directly onto the exhaust manifolds.  Not only does an oil leak 
like this make a mess but it also causes the exhaust manifold gaskets to erode.”  Note:  See page 101 regarding the liner 
sealing. 

The Haynes manual merely says to use “jointing compound”, perhaps recognizing the shortcomings of Hylomar for this 
application.  According to Craig Sawyers, his repair manual (Jaguar SIII Service Manual, AKM 9006 Ed 5, ©1988) 
“...says to use Loctite 573.  I used 574, which the Loctite website (

www.loctite.com

) has as practically the same stuff.  

TWR Jaguar in Oxford (Tom Walkinshaw's dealership, who manufactured the XJ220.  I believe they know a thing or 
two about Jags) use 574.” 

A call to Loctite (1-888-LOCTITE or +1-203-571-5100) and a discussion with a tech rep revealed the following:  First 
off, Hylomar (which is also made by Loctite, under license from Marston Bentley Ltd.) is intended as a gasket dressing, 
not to be used without a gasket at all, and is not recommended for this application.  As Sawyers says, either 573 or 574 
is suitable; the chief difference is in difficulty of disassembly, since 574 will glue the parts together pretty well while 
573 is designed to be easier to get apart. 

573 is bright flourescent green and 574 is orange -- the stuff itself, not the tube it comes in.  Loctite products all seem to 
come in red tubes. 

Sawyers reports that you’ll need about 50ml to do both banks.  573 in a 50ml tube is Loctite part number 21455 and 
574 in a 50ml tube is part number 24018.  Unfortunately, neither 573 or 574 is commonly sold in auto parts stores.  
Finding it will normally entail calling Loctite at the above number and getting the name and number of a local 
distributor; Loctite will not sell it direct.  Neither of the substances is cheap, but worse yet you may end up facing a 
minimum order requirement of 10 tubes or some such, so you might want to talk your local Jag club into placing an 
order for the group. 

Now, according to Neal, apparently Jaguar has changed its mind again about what to use on the tappet block/head joint 
-- perhaps because Loctite 573 and 574 are too difficult to find.  “I'm more partial to Loctite 518 which, by the way, is