[v12-engine] Valve Rattle

Tom,

It was worthwhile looking at the PCV valve!
There’s my rattle. What did you replace your’s with? Parts stores don’t
carry that type, and it’s unusual in size (diameter) and spring return. I
wonder if a new one (OEM) will stll be noisy?
Have you got your steering rack together again?

Thanks,
Len

Orginal message--------
Kirby,
Thanks for the response.
I’m afraid your answer and description sounds like bad news for me and my 85
XJ-S. (See the rest of my response below your reply).

original message>>>>>.
rattling noise". John, Kirby and others, can you describe this noise
for those of us who think we hear it (or fear it), and to
differentiate it from high mileage valve rattle or ticking?.

Mine sounded EXACTLY like a Chevy with a bad >lifter. Note, however,
that on mine, the valve had fallen about 1/8" but had not >come out.
If it comes out, I suspect the sound would be different.

I’ve never heard a Jag V12 with a high mileage valve >rattle or ticking.
---- Kirbert

snip >>>

valve seat.
I thought it would be constant.
Can you tell me what are some of the other symptoms?
I have not driven another XJ-S enough to compare, but I am surprised and
shocked at how many of my friends with XJ-S’s disregard or avoid looking
into loss of top end power (because they never use it or don’t realize their
rev’s stop at 4,000 or so (my advance WAS sticking, but is now serviced and
freed up, but I still have to rebuild the vac advance module).
Boy, am I surprised to hear that Jag V12’s never develop valve rattle or
ticking. Does that mean that such sounds translates that it’s always a
dropped valve seat?

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It was worthwhile looking at the PCV valve!
There’s my rattle. What did you replace your’s with? Parts stores
don’t
carry that type, and it’s unusual in size (diameter) and spring
return. I wonder if a new one (OEM) will stll be noisy?

Aren’t they SUPPOSED to rattle? I thought that the test was to take
it out and shake it. If it rattles, put it back in. If it doesn’t
rattle, you need a new one.

OTOH, I’m not entirely sure that it rattling while the engine running
isn’t a symptom of another problem. Vacuum and crankcase pressure
should both be pretty stable at any given operating condition, so the
PCV valve would either be held open or held shut. If it’s rattling,
perhaps there’s a pulsing condition either in the manifold or the
crankcase or both. Which would, of course, be bad. Is the engine
physically shaking during this rattle?

Boy, am I surprised to hear that Jag V12’s never develop valve rattle
or
ticking.

Didn’t say that. Just said I’ve never heard one. Jaguar V12’s don’t
have hydraulic lifters, so they can’t go bad. But if the valve
clearances got really wide for some reason, I’m sure they’d tick.
The question is, how would they get wide? A tappet could have gotten
really worn, like it wore through the case hardening and proceeded to
wear through the softer steel underneath. I’ve seen that happen on
several cars, including a Rolls Royce, but I haven’t seen it happen
on a Jag V12 yet.

Does that mean that such sounds translates that it’s always
a dropped valve seat?

If your car sounds like a Chevy with bad lifters, I’d suggest a quick
check of your finances. One way or another, you’re gonna need 'em.

– Kirbert
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http://www.jag-lovers.org/cgi-bin/majordomoOn 11 Mar 2001, at 22:59, Len and Sheila Olsen wrote:

On 12-03-01, Kirbert told us:

OTOH, I’m not entirely sure that it rattling while the engine running
isn’t a symptom of another problem. Vacuum and crankcase pressure
should both be pretty stable at any given operating condition, so the
PCV valve would either be held open or held shut. If it’s rattling,
perhaps there’s a pulsing condition either in the manifold or the
crankcase or both.

On my 1986 car, the PCV often rattled, apparently the aerodynamics of the
valve caused the piston to oscillate at certain manifold pressures. I came
to the conclusion that is was just a bad design (made by a Delco company )

Which would, of course, be bad. Is the engine
physically shaking during this rattle?

Boy, am I surprised to hear that Jag V12’s never develop valve rattle
or
ticking.

Didn’t say that. Just said I’ve never heard one. Jaguar V12’s don’t
have hydraulic lifters, so they can’t go bad. But if the valve
clearances got really wide for some reason, I’m sure they’d tick.

I think, and IIRC Bywater says that top end rattle is mostly due to lateral
clearance around the tappets. I can’t say that I have heard a bad one though.

The question is, how would they get wide? A tappet could have gotten
really worn, like it wore through the case hardening and proceeded to
wear through the softer steel underneath. I’ve seen that happen on
several cars, including a Rolls Royce, but I haven’t seen it happen
on a Jag V12 yet.

I do remember my brother’s XK engine at 150,000 miles having rattly
tappets due to the cams wearing through the case hardening, with the effect
that the valve clearance changed as the tappet rotated, making it
impossible to set the valve clearances accurately. I suppose the same
thing could happen on the V12, as the tappets are the same.

Does that mean that such sounds translates that it’s always
a dropped valve seat?

Remember that probably only one or two valve seats will drop at a time, but
noise due to wear will probably be present on many valves, so you should be
able to tell a lot by listening carefully.

regards,
Mike

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