Jaguar XJ-S. Manual - part 19

 
 

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red.  Loctite 518 is a metal to metal sealer and dries to a rubbery texture.  It is what Jaguar now recommends for sealing 
the cam towers to the heads.  Most auto parts stores carry it, just get the big tube.” 

Joe Bialy says, “I have a copy of "Loctite Worldwide Design Handbook" 1996/97 edition.  518, 573, and 574 are all 
from the same family of gasketing materials.  573 cures slow and fills gaps up to 0.2mm.  518 has moderate cure time, 
fills gaps to 0.5mm.  574 is fast curing, good for 0.5mm gaps.  They are intended primarily for structurally rigid close 
fitting flanges.  Being anaerobic, they only cure between the flange faces.  Excess material is dissolved in "most fluids" 
thus flushed away.  "Passages or channels will not be blocked." 

“The book makes no mention of Hylomar at all.”  Interesting, since Loctite manufactures Hylomar under license. 

“I also saw a Jag tech bulletin (#12-51) that now specifies Loctite #518 for the tappet block-to-head joint. It was dated 
8/94.” 

“Also according to their book for 510 type gasket compounds (509, 510, 518, 573, and 574):  "Anaerobics cure rapidly 
between metal surfaces...To ensure gasketting success, all fasteners must be torqued to specification immediately (<3 
minutes) after assembly".  I dunno how you’d torque any assembly to spec within three minutes, especially one with as 
many fasteners as the tappet block-to-head joint, especially if you include the cam bearing caps in that spec.  
Nevertheless, the substances do seem to provide a good seal. 

David Johnson points out that Loctite provides an online comparison of the various gasket-forming substances they 
offer at 

 

http://www.loctite.com/literature_html/pdf/gasketingan.pdf

 

This is a .pdf file, which means you’ll need Adobe Acrobat to view it -- but the Adobe Acrobat reader is free, if you 
don’t already have it you should get it anyway. 

Steve Cranswick suggests Loctite 5900, as described on page 39.  I know, too many recommendations, but the point is: 
just about any Loctite 500-series product will probably work here.  What won’t work here is Hylomar, which is what is 
recommended in the early ROM’s and was probably used at the factory on early cars. 

Whatever sealant you end up using, think a little bit before applying it.  There is no need to smear it all over 
everywhere, and in fact that type of application is not recommended because it can result in air bubbles.  Keeping the 
bead thin might also help you get it compressed properly with the first few bolts before the sealant sets up.  You also 
don’t want to get any inside the tappet guides.  The instructions on the tube of 573 say to apply a bead to one part only, 
which makes it easier to apply than Hylomar; trying to “smear” it onto the head itself would be tricky since all those 
studs are in the way.  Basically, you need to apply one continuous bead of sealant completely around the edge of the 
tappet block, making sure the bead pattern is such that it will always contact a mating surface on the head.  Some flat 
areas on the tappet block correspond to gaping holes on the head, so a random guess is not acceptable; make very sure 
you are applying the bead in the correct place.  Pay special attention to the area of the inside corners right behind the 
cam sprockets, where the forwardmost cam bearing studs are located; each side of the tappet block requires a slightly 
different treatment, and the left bank is a bit different than the right. 

Now, think a little more before applying the sealant.  Note that the bead should be routed inside of each of the 10 holes 
(one row of 6 plus the 4 surrounding the sprocket) for the studs on which the nuts are located outside the cam cover.  
Unfortunately, depending on the casting tolerances of your particular tappet block, the amount of surface area just 
inside the 6 holes may be tiny indeed; you will need to exercise considerable care to make sure that particular location 
seals properly when assembled.  Also note that the bead must be located outside of the other 20 holes, otherwise oil 
might get under a nut, run down a stud and leak out -- a serious potential on the studs that hold the cam bearing caps, 
since oil is being fed under pressure between those parts.  

If all that wasn’t perfectly clear, I have provided an illustration showing where that bead of sealant should be located; 
see Figure 5. 

 
 

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Figure 5 - Sealing the Tappet Block 

 
 

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If you have a pre-’84 car with 5/16” studs, the 4 studs surrounding the cam sprocket have been sealed with cap nuts and 
copper washers.  However, if the bead of sealant is applied to the tappet block correctly inward of these studs and the 
cam cover gasket does its job, there will be nothing within these stud holes to leak.  From ’84 on, these 4 studs are 
metric and use normal nuts and spiral groove washers with no attempt at sealing the studs, so they must have figured 
out it wasn’t necessary. 

 

VALVE CLEARANCES:  In order to adjust the valve clearances, you must tear a considerable amount of hardware off 
the top of the engine.  Also, since adjustment is via shims, the measurements must be made, the assembly torn apart and 
the shims removed and replaced, and the gaps checked again after reassembly.  The shims themselves cost about $3 
each.  Having a dealer perform this work reportedly costs over $600, and is probably a reasonable charge considering 
the number of hours that will be required.  Before doing the work yourself, see the tip on clearing off the top of the 
engine on page 58. 

The wear rate on this valvetrain is slow, so this adjustment doesn’t need to be done very often.  However, when they do 
need adjustment, it’s likely because the clearances have closed up!  Wear between cam lobes and tappets or between 
tappets and valve stems causes the gaps to open up while wear between valves and seats causes gaps to close, and 
apparently the latter is predominant in this engine.  This means that there won’t be an annoying ticking to tell you that 
the valves need adjusting. 

If you wish to check clearances, it is recommended that you obtain a set of feeler gauges that has a bend in the blades.  
You can’t get a straight blade in there, but sets are available wherein the entire set of gauges and the holder they come 
in are bent about 45º in the middle. 

A minor tip:  The valve adjusting pads come in sizes varying in .001” increments and (the genuine Jaguar parts 
anyway) indicated by a letter etched on one side of the pad.  As a favor to the next guy who’ll be working on this 
engine, install the pads with the letter facing outward (toward the tappet).  Years later, the letter will still be legible.  If 
installed with the letter facing the end of the valve, it will be difficult or impossible to decipher the letter later on. 

Roger Bywater of AJ6 Engineering (and formerly with Jaguar) says, “we knew back in the 1970s that running with the 
exhaust valve clearances set at 0.016” gives a slight but measurable gain in mid-range torque and reduced fuel 
consumption.  Noise is not excessive at this setting because the actual running clearance closes up with the higher 
temperature of the exhaust valves compared to the inlets which must be set as normal. 

“Anyone wishing to measure a V12 cam, as I have done in the past, will find that the timing quoted for the H.E. occurs 
at 0.010” lift whilst the timing at the point at which 0.012” clearance is taken up is an almost unbelievable 36,78/78,36. 
 The difference in overlap between 0.013”  and 0.016” clearances is about 12 degrees so the need to avoid tight 
clearances will be obvious and although the extra lift may be insignificant it can profoundly effect the HC emissions 
generated, quite apart from the modest effect on torque.  In my view the best compromise regarding noise and 
performance is to aim for 0.013” for inlets and 0.015-0.016” for exhaust which, because of greater expansion of the 
exhaust valve stem, results in a similar true running clearance for both. 

“...If mid-range torque could be improved by just opening up the clearances, why did the factory not do it in 
production?  Well maybe they did (I am not prepared to be more positive than that) - but you will not find any manual 
telling you so because the reason for doing it would have been to reduce HC emissions at a critical time, at the risk of 
introducing more tappet noise problems.” 

 

CYLINDER HEAD REMOVAL:  First, a bit of clarification:  It is possible to remove each head with the camshaft and 
tappet block in place, and this may make sense if the reason for disassembly is farther down.  This is the procedure 
outlined in both the ROM and the Haynes manual.  On the other hand, if you plan to work on the tappets or valves 
anyway, you might choose to remove the camshaft and tappet block before removing the head.  It makes the head 
lighter for lifting, and it makes it safer to set down -- there won’t be any valves sticking out the bottom. 

The following are a few comments/corrections to the ©1975 ROM, Sections 12.29.11 and 12.29.12, along with 
corresponding sections of the Haynes manual: 

 
 

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In Section 12.29.11, which is about pulling the B bank head, step 19 deals with moving the transmission dipstick tube 
outta the way.  The dipstick for the BW tranny is on the B side, but on the cars with the GM400 the dipstick is over on 
the A side, so this step needs to be moved to Section 12.29.12.  The same thing might be said of step 14 in Chapter 1, 
Section 19 of the Haynes manual -- that it should be moved to Section 20 -- but if you have a later car, you should 
probably be following the procedures outlined in Chapter 13, Section 3 anyway. 

In Section 12.29.12, which is about pulling the A bank head, step 5 says to remove the auxiliary air valve.  The AAV is 
on the B side, and doesn’t need removal for working on the A head only.  The same correction applies to Chapter 1, 
Section 20, step 5 in the Haynes manual. 

Steps 8 and 12 in section 12.29.11 and steps 10 and 14 in section 12.29.12 instruct you to position the engine at TDC 
on cylinder 1A (by using the cam aligning tool on the notches in the camshafts) and then unbolting the sprockets from 
the camshafts.  You will find this job goes easier if beforehand you rotate the crank one full revolution from that 
position (TDC on cylinder 6A, notches on cams pointing downward towards the head) and pull two bolts and one 
locking plate off of each sprocket.  They’re easier to get to when pointing up than when pointing down.  Step 7 of 
Section 12.13.01 and step 6 of Chapter 1, Section 10 of the Haynes manual hint in this direction without making it as 
clear as they might. 

Both manuals talk about removing heat shields, but beyond the big obvious one on each side don't really clarify what 
they're talking about.  In all probability they're referring to the heat shield on the downpipe on the LH side as well as the 
heat shields around the boots on the power steering rack.  The heat shields on the rack need to be removed in order to 
deal with the downpipes. 

Neither manual even mentions the front exhaust manifolds.  It’s probably a matter of choice; they can either come off 
with the head or separately.  If left attached to the head, they provide a nice handle for grabbing, but they do make the 
assembly heavier to lift. 

 

CYLINDER HEAD REMOVAL -- ENGINE IN CAR:  The conundrum facing anyone pulling the heads with the 
engine in the car is the fact that the rear exhaust manifold on each side is too close to a portion of the chassis.  If the 
head is slid up the studs with the rear manifold still bolted to it, it will hit the chassis long before the head clears the 
studs.  This problem can be addressed in two ways:  1) the rear manifolds can be removed from the head first; or 2) the 
motor mounts can be disconnected and the engine moved around until the manifolds clear the chassis as the head comes 
off.  Sections 12.29.11 and 12.29.12 of the ROM describe the first option.  Section 12.29.12 for the A bank head also 
describes pulling the starter, which is probably entirely to gain access to the lower nuts on the rear exhaust manifold on 
that side; if the head is removed with the rear exhaust manifold attached, the starter does not need to be removed. 

If you choose the path of removing the manifolds first, you’ll run into the same problem: the chassis is too close.  The 
manifold won’t come over its own studs without hitting the chassis first.  Of course, sections 30.15.10 and 30.15.11 of 
the ROM just list the step-by-step instructions as though each step is easily completed.  After all the fun you’ll have 
getting a wrench on the nuts on the bottom side of the manifolds, you’ll be just tickled pink to find that you have to 
undo the motor mounts and tilt the engine anyway. 

This manifold removal problem also has two possible solutions:  A) move the engine on its mounts again; or B) 
unscrew the studs so the manifold can come out vertically without having to clear the studs.  Of course, unscrewing the 
nuts is hard enough, unscrewing the studs is likely to be seriously difficult.  Here’s an idea:  Remove all the nuts first, 
then back the manifold up against the chassis so you have a gap between the manifold and the head.  Using a thin pair 
of pliers, reach between the gap and unscrew the top three studs and then the bottom three studs.  This method has the 
advantage that you will be gripping the studs near the middle and therefore not boogering up the threads where they’re 
actually used.  Note that two of the studs on the bottom of each rear exhaust manifold cannot come out through the 
manifold; they will either have to be removed with the manifold or the manifold will have to be repositioned -- perhaps 
downward, perhaps tilted -- to get those studs out.  All the while, keep in mind that you will have to put this manifold 
back on somehow. 

Clearly, removing the heads by leaving the manifolds on the heads and tilting the engine has its benefits.  For one thing, 
you can leave the starter alone, there’s no reason to mess with it.  This author got his heads off by unbolting the motor