[v12-engine] valve clearance adjustment - what to know

V12-Engine
1

After all that was discussed here in the topic ‘‘mildly
erratic engine response’’, I’m planning to soon adjust the
valve clearances of my engine. I know this might sound as a
simple work for most of you, but pls consider that in my
country a Jaguar is a strange thing and that I’ve never seen
the innards of a Jag V12 engine (though I’ve successfully
rebuilt a BMW V12 engine). When I say that, what I mean is
that I’ve supervised a mechanic (who knew nothing about that
particular engine) doing it. I’m a mechanical engineer in
the business of motorcycle engine repair and rebuild.

So far I’ve read Kirby’s book related pages and also looked
at Bernard Embden’s www site explaining how the timing chain
tensioner works. BTW, tks to both of them! Anyway, and
though my English might seem quite OK (it’s my 3rd
language), I always fear to misunderstand something. So here
a couple of questions:

  1. Brittle tensioners tend to break when fully retracted
    (straight position), that’s a fact. After explaining all
    possible precautions to avoid it breaking, Kirby’s book
    tells you NOT to retract it and just let the sprockets
    engaged in the chain and hanging from hooks in the housing.
    When re-installing camshafts just rock the latch to release
    the extra chain tension. IS THIS SO? Or did I understand
    something wrong?

  2. Cam cover oil leaks are no news, especially the moon
    seals. Did I understand correctly that one solution is to
    put new half moons, but NOT to put ANY gasket and use
    ‘‘gasket maker’’ cement all the way and especially above and
    below the new half moon??? (BTW I’ve used in the past a very
    good German made ‘‘Victor Reinz’’ brand gasket maker that I
    can easily buy locally). This would allow me not to need to
    import the gaskets, with the big risk of them being nicked
    (destroyed) in transit or customs.

  3. As most probably I’ll have to enlarge the valve clearance
    gaps, I’m tempted to lower the existing shims, also to avoid
    the complicated freight and customs bureaucracy involved in
    importing new finer shims. I know a guy with the proper
    tooling (a magnetic bench) to do such work. Does anyone see
    a problem here? Or should I better go for thinner original
    shims?

Additionally, I’d appreciate any kind of advice from you
experts regarding this work.

Tks in advance & rgds, Luis.

PS The saga ‘‘in search of a more stable idle’’ will follow…–
Luis Gasperini / '91 V12 XJ-S conv. 5sp
Montevideo, Uruguay
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2

In reply to a message from Luis Gasperini sent Thu 7 May 2009:

Hi Luis.

No problem with grinding them, did that when I overhauled my engine
1990 (a long time ago :slight_smile: and no problems what so ever.

BR//Tobmag–
The original message included these comments:

  1. As most probably I’ll have to enlarge the valve clearance
    gaps, I’m tempted to lower the existing shims, also to avoid
    the complicated freight and customs bureaucracy involved in
    importing new finer shims. I know a guy with the proper
    tooling (a magnetic bench) to do such work. Does anyone see
    a problem here? Or should I better go for thinner original
    shims?

–
tobmag
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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3

Luis Gasperini wrote:

  1. Brittle tensioners tend to break when fully retracted
    (straight position), that’s a fact. After explaining all
    possible precautions to avoid it breaking, Kirby’s book
    tells you NOT to retract it and just let the sprockets
    engaged in the chain and hanging from hooks in the housing.
    When re-installing camshafts just rock the latch to release
    the extra chain tension. IS THIS SO? Or did I understand
    something wrong?

That’s correct. Some people have even done the job and neglected to
rock the latch on reassembly and the car still runs, but apparently
makes a lot of racket because the tensioner is too tight. One quick
release to allow it back to its normal level of tension and all is
well.

  1. Cam cover oil leaks are no news, especially the moon
    seals. Did I understand correctly that one solution is to
    put new half moons, but NOT to put ANY gasket and use
    ‘‘gasket maker’’ cement all the way and especially above and
    below the new half moon???

That’s correct, except there’s nothing “especially” about going
around the half moon. In fact, the half moon is the least of your
worries when applying the sealant.

(BTW I’ve used in the past a very
good German made ‘‘Victor Reinz’’ brand gasket maker that I
can easily buy locally). This would allow me not to need to
import the gaskets, with the big risk of them being nicked
(destroyed) in transit or customs.

They’re expensive anyway! The only downside of this method is that,
eventually, the rubber half moons will harden and crumble. If you
don’t overheat the engine, that’ll probably be a good long time,
though – perhaps long enough that you’ll be looking to adjust the
valves again anyway.

  1. As most probably I’ll have to enlarge the valve clearance
    gaps, I’m tempted to lower the existing shims, also to avoid
    the complicated freight and customs bureaucracy involved in
    importing new finer shims. I know a guy with the proper
    tooling (a magnetic bench) to do such work. Does anyone see
    a problem here? Or should I better go for thinner original
    shims?

I’ll allow others to answer here. I think you’ll be OK. You
should never open the gaps by trimming the end of the valve stem
itself because it’s case-hardened, but I don’t believe the shims have
the same concern.

When resizing, I’d suggest milling off the side with the thickness
letter on it since it won’t be valid any more. You can re-mark if
you choose.

Also, if you’re clever, you may be able to shift shims around for
most of the adjustment and then only grind a handful rather than all
24.

Additionally, I’d appreciate any kind of advice from you
experts regarding this work.

First tip is easy: Don’t forget to reseal the tappet block to the
head while you’re there. You’ll kick yourself if you don’t.

Also, if you haven’t already, replace the washers under the outboard
3/8" head nuts with 1/8" thick washers. Then you might as well
retorque the entire head while you’re there. Make sure to apply
sealant on both sides of the washers under the 7/16" cap nuts, and
use anti-seize compound on all head nuts.

You might want to check the cam timing as it goes together. Chain
stretch affects the A bank more than the B. Not a biggie, though –
and if it looks like it is a biggie, like you have to adjust it a
LOT, that’s probably an indication it’s time for a new chain. At the
position you’ll be in, you’ll be able to replace the chain by
connecting one end of the new one to the end of the old one and
feeding the new one in while turning the engine over – provided you
get a new chain with a master link.

And if you haven’t already, modify or replace the banjo bolts for the
oil lines to the rear of each tappet block.

I’m sure you’re already planning to replace the screws holding the
cam covers.

– Kirbert

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4

In reply to a message from Kirbert sent Thu 7 May 2009:

Tks Kirbert!

That’s correct, except there’s nothing ‘‘especially’’ about going
around the half moon. In fact, the half moon is the least of your
worries when applying the sealant.

I just meant to put sealant above AND below the half moon.

They’re expensive anyway! The only downside of this method is that,
eventually, the rubber half moons will harden and crumble. If you

If gaskets are expensive and using instead a sealant (gasket maker)
is an appropriate solution… I don’t understand why EVERYBODY
doesn’t go that route. IOW, don’t see why ANYONE would buy a gasket.

When resizing, I’d suggest milling off the side with the thickness
letter on it since it won’t be valid any more. You can re-mark if
you choose.

Good suggestion!

Also, if you’re clever, you may be able to shift shims around for
most of the adjustment and then only grind a handful rather than
all 24.

I had already thought that… Means I’m clever??? :slight_smile:

First tip is easy: Don’t forget to reseal the tappet block to the
head while you’re there. You’ll kick yourself if you don’t.

Advice taken!

Also, if you haven’t already, replace the washers under the
outboard
3/8’’ head nuts with 1/8’’ thick washers. Then you might as well
retorque the entire head while you’re there. Make sure to apply
sealant on both sides of the washers under the 7/16’’ cap nuts, and
use anti-seize compound on all head nuts.

Will do. Engine is surely unopened. Had 14k miles when I bought it.

You might want to check the cam timing as it goes together.

OK

And if you haven’t already, modify or replace the banjo bolts for
the oil lines to the rear of each tappet block.

No I haven’t and don’t know why I should either. Will read in The
Book.

I’m sure you’re already planning to replace the screws holding the
cam covers.

Will check. Plan to start next week, but only work a couple of
hours from time to time. So it might take long for me to finish.

Tks once again Kirbert.–
Luis Gasperini / '91 V12 XJ-S conv. 5sp
Montevideo, Uruguay
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5

Luis Gasperini wrote:

If gaskets are expensive and using instead a sealant (gasket maker) is
an appropriate solution… I don’t understand why EVERYBODY doesn’t go
that route. IOW, don’t see why ANYONE would buy a gasket.

Logically, the only reason to go with the gortex gaskets and the
aluminum half moons is because the aluminum half moons won’t every
dry up and crumble. So you’re talking about a 100-year seal instead
of a 10-year seal.

Really, I don’t understand why people don’t do a lot of things. I
don’t know why anyone would ever buy a Marelli cap and rotor, either.

– Kirbert

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6

In reply to a message from Kirbert sent Fri 8 May 2009:

Luis:

The only thing I can add is that the good gasket maker sealants are
being used more and more instead of gaskets.

I know of some midnineties sbc’s that use them in lieu of exhaust
manifold gaskets a very high temp silicon seal. it seems to work
just fine.

Carl–
Carl Hutchins 1983 Jaguar XJ6 with LT1 and 1994 Jeep Grand
Walnut Creek, California, United States
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7

In reply to a message from Luis Gasperini sent Thu 7 May 2009:

Hi Luis

I retracted the timing chain tensioner but I did not retract it
FULLY fearing that would break it.

I used a piece of flat bar with a hole in the centre which lay
accross the cam box opening where the timing chain disappears
into. Through this hole I had a J-shaped threaded rod that was
bent more than 90 degrees at the bottom at the correct height to
hook the tensioner. Threading a nut over the threaded bar sticking
out the flat bar on top would then relax tenstion on the chain just
enough to be able to remove the sprockets off the cams without
drama. This also required moving the crank slightly clockwise or
anti-clockwise depending on which sprocket had to be worked on. Can
send a pic if my verbal description does not ‘‘work’’.

I also had the shims ground off to the correct size for the
required clearances.–
'73 E-type V12 OTS '87 DD6 '80XJS:http://tinyurl.com/cqyeec
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