[xj40] Very stiff inlet camshaft

My 87 cylinder head has come back gleaming from the head specialist
rebuild shop. After bolting up the camshafts to the recommended
torque, I find that while the exhaust camshaft is stiff to turn
(wedging an extension bar against temporarily inserted camshaft
flang bolts) as expected, and as experienced on many head rebuilds,
the inlet camshaft is MUCH stiffer. I did not try it before sending
away the head so cannot compare, but what is the experience of
others (no theory please – I know they should be similar)? Do the
two camshafts often require VERY different turning forces in
prcatice?–
Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Thu 17 Mar 2011:

Alan,

Is this with the head bolted down to the block? That is the
only time that the camshaft is properly torqued down by the
head bolts which pass though the camshaft bearing caps.

Did you have the head skimmed?

Its been a long while since I did that job on my car but I
do not recall any ‘stiffness’ in turning the camshafts -
only the slightly ‘lumpy’ feel as each valve spring was
depressed, but I had no difficulty turning them.

If you suspect an alignment problem of the camshaft
bearings, the only way to check that would be to remove all
of the valves to let the camshafts ‘freewheel’ in those
bearings.–
The original message included these comments:

My 87 cylinder head has come back gleaming from the head specialist
rebuild shop. After bolting up the camshafts to the recommended
torque, I find that while the exhaust camshaft is stiff to turn
(wedging an extension bar against temporarily inserted camshaft
flang bolts) as expected, and as experienced on many head rebuilds,
the inlet camshaft is MUCH stiffer. I did not try it before sending
away the head so cannot compare, but what is the experience of
others (no theory please – I know they should be similar)? Do the
two camshafts often require VERY different turning forces in
prcatice?


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Thu 17 Mar 2011:

Yes Bryan, the head was skimmed automatically during the recon
procedure. Point taken about head bolts, not bolted onto the block
yet, but my worry is that the inlet is so much stiffer than the
exhaust. I too am very familiar with the ‘lumpiness’ of the valves
being compressed, but on the inlet the force is so great as to mask
that. I cannot test the alignment without unspringing the valves,
can I? I am going to try and isolate which bearing cap gives the
problem, as it’s only on tightening up that I have the trouble.
Then I am wondering if some slight application of very fine emery
cloth on the appropriate bearing is a good idea. It is perhaps
surprising that these bearings are just steel in aluminium, unlike
the Ason Martine top end I did when I seem to remember that the
bearings were white metal in shells.–
Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Thu 17 Mar 2011:

Alan:
I agree with Bryan. The cams shouldn’t be that hard to turn.
But they have to turn TOGETHER because the valve will interfere
with each other if both intakes and exhausts are opened at the same
time. If you’re turning the cams separately (I hope and pray that
didn’t do that), you’re going to bend valve stems, and it will have
to go back to the head guy.–
The original message included these comments:

My 87 cylinder head has come back gleaming from the head specialist
rebuild shop. After bolting up the camshafts to the recommended
torque, I find that while the exhaust camshaft is stiff to turn
(wedging an extension bar against temporarily inserted camshaft
flang bolts) as expected, and as experienced on many head rebuilds,
the inlet camshaft is MUCH stiffer. I did not try it before sending
away the head so cannot compare, but what is the experience of
others (no theory please – I know they should be similar)? Do the
two camshafts often require VERY different turning forces in
prcatice?


Pete Peterson 70E(193K) 88XJ40s(253K & 242K) 94XJ40 (122K)
Severna Park, Maryland, United States
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In reply to a message from Alan4d sent Thu 17 Mar 2011:

Alan,

I don’t want to be the bearer of bad news, but if the reason
that the head was skimmed was because it had warped
slightly, releasing the pressure on the head bolts would
allow the head to ‘spring’ in the direction of the warp and
thus ‘bend’ the camshafts. That would mean that you would
have perhaps felt that ‘stiffness’ if you had tried to turn
the camshafts as soon as you took the head off.

It is therefore possible that with the new flat surface of
the head to block face, when you torque down the head bolts
on the block the camshaft ‘bend’ may straighten out or could
be made worse.

I did not need to get the head skimmed on my car - it was
perfectly flat when removed.

I do know that there is definitely some tiny deflection of
the camshaft when the head is properly torqued to the block
as opposed to the head being on the bench with the bearing
caps merely held down with its own bolts (which is I guess
the situation you have now?). IIRC, I found that the valve
clearances would reduce by varying amounts up to about 1�
to 2 thou between the clearances on the bench and those when
the head was fitted to the block and fully torqued down.
That must indicate a deflection in the camshaft when finally
fitted.

I don’t recommend using emery on bearing surfaces. Those
bearings are line-bored at the factory.

I would try bolting it down to the block (use the old gasket
temporarily) to see if the stiffness disappears.

Watch that the valves don’t clash with the pistons or each
other when turning the camshafts individually.–
The original message included these comments:

Yes Bryan, the head was skimmed automatically during the recon
procedure. Point taken about head bolts, not bolted onto the block
yet, but my worry is that the inlet is so much stiffer than the
exhaust. I too am very familiar with the ‘lumpiness’ of the valves
being compressed, but on the inlet the force is so great as to mask
that. I cannot test the alignment without unspringing the valves,
can I? I am going to try and isolate which bearing cap gives the
problem, as it’s only on tightening up that I have the trouble.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Alan4d sent Thu 17 Mar 2011:

Forgive my impudence at such a basic suggestion - but I
trust the camshafts have had a liberal coating of assembly
lube applied to the bearing journals before assembly? They
aren’t being turned in bone dry bearings are they?–
The original message included these comments:

My 87 cylinder head has come back gleaming from the head specialist
rebuild shop. After bolting up the camshafts to the recommended
torque, I find that while the exhaust camshaft is stiff to turn
(wedging an extension bar against temporarily inserted camshaft
flang bolts) as expected, and as experienced on many head rebuilds,
the inlet camshaft is MUCH stiffer. I did not try it before sending


1990 4.0 Sovereign
Canberra, Australia
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In reply to a message from Jaguarpete sent Thu 17 Mar 2011:

Well, that would chill me soemwhat, but I am happy to report that
the inlet camshaft was not THAT difficult to turn and the exhaust
was easy! So I surmise that the valves don’t actually meet on this
model (said he hopefully). If there were valve clashes surely the
reistsnce would be very extreme? I’ve found that Nos 5 and 6 caps
on the inlet were reversed during rebuilding, so maybe that’s been
the problem.–
The original message included these comments:

I agree with Bryan. The cams shouldn’t be that hard to turn.
But they have to turn TOGETHER because the valve will interfere
with each other if both intakes and exhausts are opened at the same
time. If you’re turning the cams separately (I hope and pray that
didn’t do that), you’re going to bend valve stems, and it will have
to go back to the head guy.


Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Fri 18 Mar 2011:

Alan,

I can assure you that with the head on the bench, a) you
have to raise the head on blocks so that the fully open
valves do not hit the bench and b) you need to turn the
camshafts in unison a few degrees at a time, always in a
clockwise direction, from the TDC #1 cylinder timing
position to avoid the valves on one side clashing with the
valves on the other.

It takes very little effort to bend a valve stem if the
valves clash.

With the head bolted down to the block, you should not
attempt to turn the camshafts individually or in unison
prior to the cam timing being set in relation to TDC #1
cylinder unless you are sure that none of the pistons are
anywhere near TDC on any cylinder.

This is an ‘interference’ engine and valve / piston damage
will occur otherwise.–
The original message included these comments:

Well, that would chill me soemwhat, but I am happy to report that
the inlet camshaft was not THAT difficult to turn and the exhaust
was easy! So I surmise that the valves don’t actually meet on this
model (said he hopefully). If there were valve clashes surely the
reistsnce would be very extreme? I’ve found that Nos 5 and 6 caps
on the inlet were reversed during rebuilding, so maybe that’s been
the problem.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Fri 18 Mar 2011:

Hi all

Thnaks very much for your input. It is my hope that I have not bent
any valves. The exhaust cam turned very easily. I don’t think I
turned either cam all the way round. I will have a look today. I
asume if any valve is bent it will not seat and I will be able to
see it?–
Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Fri 18 Mar 2011:

Alan,

Not easily - depends how badly it is bent. The only way to
check for a bent valve is to remove it and spin it to see if
there is any run-out or to lap it against the seat to see if
you get 100% contact all the way around the valve head.

Have you solved the ‘stiff’ rotation of that camshaft by
re-fitting the bearing caps in the correct order?–
The original message included these comments:

Thnaks very much for your input. It is my hope that I have not bent
any valves. The exhaust cam turned very easily. I don’t think I
turned either cam all the way round. I will have a look today. I
asume if any valve is bent it will not seat and I will be able to
see it?


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Fri 18 Mar 2011:

Hi Bryan

Thanks for your help. No I have not tested it because I am now
nervous about rotating a camshaft with the other in place. I am
hoping to go down to the workshop this morning and I will remove
the two cams, bolting them up one at a time, which is what I should
have done in the first place!

I am very unhappy about the prospect of slightly bending a valve
and not being able to see it. Looks as though I will have to
dismantle the whole head! I was hoping a bend would be obvious or
there would be some other test with the valves still in the head. I
suppose I could try putting fluid in the chamber(preferably not
petrol) and see if any leaks through.–
Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Fri 18 Mar 2011:

Bryan, further to that I have received an email asking whether the
head was on the block. This makes me hopeful because the head is
off the block and up on the bench, with spacers under it. Do you
think that bodes well for the valve bending scenario?–
Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Fri 18 Mar 2011:

Alan,

This is just an illustration of the problem.

If you start off with the camshafts in the correct ‘TDC #1
cylinder’ position - i.e with the timing slots in the
flanges exactly vertical to the plane of the head - and then
turn the inlet camshaft 40� in a clockwise direction, using
the ‘rule of seven’, the inlet valves of cylinder #6 will be
fully open.

If you then try to turn the exhaust camshaft
anti-clockwise through 40�, the exhaust valves of cylinder
#6 would also be fully opened - but before you can achieve
that , the exhaust valves will clash with the inlet valves
on cylinder #6 and if you force the issue, damage will
occur. Of course, if the valve stem is badly bent, the valve
will not close anyway because it will jam in the guide and
you would be able to see that pretty clearly. In addition,
on any bent valve, the valve clearance on that valve would
be excessive when the heel of the cam is on the cam follower

  • far greater than its original 12 to 14 thou which I
    presume your machine shop has set the clearances at.

The head does not need to be on the block for that to happen

  • that would only worsen the situation if any valve came in
    to contact with a piston before the timing is properly set.

Having said all of that, you surely didn’t apply brute force
to persuade the ‘stiff’ camshaft to rotate, did you - i.e
sufficient to bend a valve?–
The original message included these comments:

Bryan, further to that I have received an email asking whether the
head was on the block. This makes me hopeful because the head is
off the block and up on the bench, with spacers under it. Do you
think that bodes well for the valve bending scenario?


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Fri 18 Mar 2011:

No Bryan, I did not apply ‘brute force’. I merely noted that
levering round the cam by using a small extension bar (200mm)
against the sprocket bolts screwed back into the flange, resulted
in the inlet being 25% more hard to turn than the exhaust.
Whichever camshaft wasn’t being turned, the other remained with the
notch dead upwards.

I realise now that it was stpid. I’ve done top overhauls so many
times I’m amazed I forgot!

Anyway, Bryan and all else who have kindly helped, good news. This
morning, I unbolted both camshafts so that the valves reseated. I
filled each port with metho (rather than petrol because of the
danger and rather than kerosene because it would be hard to see any
oozing amongst the light coating of oil on the re-conned head). I
filled each port to the brim with the metho so that there a
meniscus. After a few minutes no oozing was detected and the level
of liquid in each port remained full, so I surmise that by
coincidence(?) I got away with it (I wonder how far I would have to
turn each camshaft if the other one was at ‘notch on top’ before
there would be a serious collison of valves?), or any touching?
(bending?) was so slight that it did not affect the integrity of
the seating seal. I suppose the ultimate test is the compression
when the engine is back together (provided the rings are OK!). I
reiterate the the exhuast was easy to turn and no point of actual
resistance was felt (although I can’t be sure how far I turned
either; my guess if 180 degrees!

In answer to the earlier question, testing with only one camshaft
in reveals that the inlet is still very stiff with the bearing caps
put properly! In fact it seemed slightly stiffer. The local
mechanic in whose garage I’m doing this thinks it is OK.–
Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Fri 18 Mar 2011:

Alan,

Sounds as if you may be OK - go for it.

If you have time (and the patience - remembering to only
turn the two camshafts in unison in the same direction to
avoid valve clash!) measure the valve clearances on the
bench and then measure them again when you have finally
torqued the head down on to the block and set the cam
timing. You may be surprised at how much they close up.

That is important if the exhaust valve clearances have been
set ‘a little tight’ on the bench because if they drop much
below the recommended minimum of 12 thou there is a chance
that the exhaust valve will not seat properly when the
engine is hot and the valve head seat will get burnt. Just
to be on the safe side, I set the exhaust valve clearance on
mine at 14 or 15 thou on the bench and all dropped 1 or 2
thou when bolted down on the block to be just within spec.

BTW, I use the ‘rule of seven’ when checking the valve
clearances. When #1 are fully open (which is easy to see),
#6 have maximum valve clearance, when #5 are fully open, #2
have maximum clearance, when #3 are fully open, #4 have
maximum clearance and so on … so that the sum of the two
cylinders always totals seven.

One other tip - do not use the torque figure of 16 to 20
lbf/ft on the camshaft bearing cap bolts quoted in Haynes -
it is too high and the bolts may snap. The correct figure is
13 to 16 lbf/ft (or 18 to 22 Nm if you work in metric)–
The original message included these comments:

In answer to the earlier question, testing with only one camshaft
in reveals that the inlet is still very stiff with the bearing caps
put properly! In fact it seemed slightly stiffer. The local
mechanic in whose garage I’m doing this thinks it is OK.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Sat 19 Mar 2011:

Oh, I wish I’d known that before! Four of my bolts stretched
(rather than snapped) and needed replacing! That torque being
wrong would explain it!

I’ll deal with another associated problem (possibly not one?) in a
fresh thread about hydraulic tensioners!–
The original message included these comments:

One other tip - do not use the torque figure of 16 to 20
lbf/ft on the camshaft bearing cap bolts quoted in Haynes -
it is too high and the bolts may snap. The correct figure is
13 to 16 lbf/ft (or 18 to 22 Nm if you work in metric)


Alan (XJ40 3.6L 1987/8)
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In reply to a message from Bryan N sent Sat 19 Mar 2011:

Further to the cam cap torque issue, the Jag workshop manual says
23-27 Nm! Do you feel that is a misprint (wouldn’t surprise me)?
Do you feel the head bolts are right at 38-40 Nm + 90 degrees (I
don’t like that last bit myself!)–
Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Sat 19 Mar 2011:

Alan,

Where did you get that head bolt torque figure of 38-40 Nm?

That’s far too low, it should be 60 (sixty) Nm (or 44
lbf/ft) plus 90�.–
The original message included these comments:

Further to the cam cap torque issue, the Jag workshop manual says
23-27 Nm! Do you feel that is a misprint (wouldn’t surprise me)?
Do you feel the head bolts are right at 38-40 Nm + 90 degrees (I
don’t like that last bit myself!)


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Sat 19 Mar 2011:

You are quite right of course! The misprint is in the Jaguar
sowrkshop manual (all $400 worth of it!) in volume 2 on page 12-
68. That misprint answers my other question! If they can make
such a gross mistake they can make any more!–
The original message included these comments:

Where did you get that head bolt torque figure of 38-40 Nm?
That’s far too low, it should be 60 (sixty) Nm (or 44
lbf/ft) plus 90�.


Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Sat 19 Mar 2011:

Job complete! Camshaft was still stiffer on the inlet than the
exhaust, but I managed to avoid bending any valves when I foolishly
turned one camshaft when another was torqued down. Anyway, top
finally reassembled into the car yesterday. Engine started on first
twitch of the key (better tn it ever has) and ran sweetly.–
Alan (XJ40 3.6L 1987/8)
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