[xk-engine] Rebuild of an S3 4.2: Whether to deck the block?

Hi all,

I’m rebuilding (first timer) a S3 donor engine for use in
my XJ6 Coupe.
History of this engine is known to be 135k miles and a
smooth runner, but giving it a going through just to be
safe. Tear down shows all of the typical wear; nothing
extreme, all original, no prior rebuild evidence. So far
all is in spec, except crank main and pin journals
marginal and will be reground .010 under.
Then the block deck; I’m getting a .003 feeler gauge
under straightedge placed between cylinders 3 and 4. A
.002 slides through in a couple other places.
I don’t see a limit spec in the shop manual. It had no
gasket leaks when running. Is .003 too deep for decking?
Is .003 no big deal? As noted, no problems when last
running. Plan is to keep relaxed ~8:1 compression. Should
mention that I did have the head shop do a first decking
of the head during rebuild.
Thoughts?–
Matt Curry, '75 XJ6 Coupe
Seattle/WA, United States
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In reply to a message from MJC 75 XJ6C sent Tue 9 Jun 2015:

If you don’t deck it and it leaks, what would you have to
pay to not have that situation? Do it now and $ave. Really
no downside to decking, as long as the piston height doesn’t
come up too close to the head, significant with 9:1 and
multiple decking, you won’t have that problem
Doug–
The original message included these comments:

running. Plan is to keep relaxed ~8:1 compression. Should
mention that I did have the head shop do a first decking
of the head during rebuild.


Douglass Harroun
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In reply to a message from Douglass Harroun sent Wed 10 Jun 2015:

I have to say this… If you do have it decked then
please ensure you fit the front timing case cover first.
They must be machined together, otherwise you will a step
at the front which will not seal. PLEASE do not ask how I
know.–
The original message included these comments:

In reply to a message from MJC 75 XJ6C sent Tue 9 Jun 2015:
If you don’t deck it and it leaks, what would you have to
pay to not have that situation? Do it now and $ave. Really
no downside to decking, as long as the piston height doesn’t
come up too close to the head, significant with 9:1 and


Phil.D 3.8 etype, XJR6, XK150 FHC, 2.2 diesel Xtype
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In reply to a message from Phil.Dobson sent Wed 10 Jun 2015:

All good points. No time like the present and thanks for
the reminder re the timing cover. :slight_smile:
Will update as things progress.
-Matt–
The original message included these comments:

I have to say this… If you do have it decked then
please ensure you fit the front timing case cover first.
They must be machined together, otherwise you will a step
at the front which will not seal. PLEASE do not ask how I
know.


Matt Curry, '75 XJ6 Coupe
Seattle/WA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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In reply to a message from MJC 75 XJ6C sent Wed 10 Jun 2015:

Yours is right on the borderline and I am a fan of never
removing metal unless you have to. But having measured it
at 3 thou and a couple of 2 thou spots you should kiss it
clean and flat. If your head is warped and you skim that,
then also take the minimum off and straighten it before
you do, if it’s out by much. Otherwise skim and get the
cam bearings align honed. Skimming a warped OHC head flat
at the gasket face only, makes camshaft binding a
permanent feature. Plus remember every bit you take off
raises your CR (and pinking tendency) whilst slackening
your timing chain.

Pete–
1E75339 66 D, 1R27190 70 FHC, 79 S2 XJ12L
Gaithersburg, Maryland, United States
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In reply to a message from PeterCrespin sent Thu 11 Jun 2015:

Thanks Pete.
Indeed reading some other threads about shaving’s effect
on timing chain tension is what led me to post the
question. I will be using new guides and tensioner for the
chain, so hopefully that will take up any slack.

Thanks again to all.–
Matt Curry, '75 XJ6 Coupe
Seattle/WA, United States
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In reply to a message from MJC 75 XJ6C sent Fri 12 Jun 2015:

Head and block shaving have the same effect and are
cumulative of course. A very fee thou for clean-up have
little effect but once you start doing heavy head cuts you
need to be careful. Even then, ORIGINAL grade parts should
cope, but a marginal chain and a marginal (sometimes
undrilled) hydraulic tensioner and a badly repositioned
guide can result in the tensioner pulling out of its shoe
and jamming crooked, followed by rapid wear on the pad and
an unholy mess in the timing drive department. You should
be fine.–
1E75339 66 D, 1R27190 70 FHC, 79 S2 XJ12L
Gaithersburg, Maryland, United States
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