Re: [xj-s] Valve Stem Seals

["Kirbert" <palmk@mailer.gadcomm.net>]

> From:          "David Low" <dkl@lbwf.gov.uk>
> 
> The Jaguar engines, from the outset were designed to be relatively 'loose',
> and always burned/used/consumed some oil.

I don't think so.  This was true of earlier engines, including my 
Triumph GT6.  However, it certainly is not an option for any car that 
has to meet US emission standards.

> If you start reducing the oil feed to stems, especially exhaust valves, you
> are going to cause localised overheating.

IMHO, doubtful.  The valve guides are pressed into an aluminum head 
that is cooled by liquid coolant -- IOW, the valve guides themselves 
are going to be cool if the cooling system is working.  If any oil at 
all leaks down the guide, it won't be enough to do any significant 
cooling.  The other end of the valve is facing combustion heat; 
enough oil flow to counteract this heat would be a major leak indeed.

If I understood Carpentier's insinuations correctly, he may be 
suggesting that the lack of sealing is one of the factors that CAUSES 
overheating of the exhaust valve stem.  When it's sealed, only the 
head and tulip gets hot, as expected.  But if exhaust gases are 
leaking up the guide, then they heat the stem all the way up.

> Other items in this newsgroup
> indicate to me that overheating appears to be a real problem in the USA.

Unrelated.  We're talking about overheating the head after shutdown 
causing the valve seats to drop.

> If you overheat a valve at the stem/guide interface, you will at best
> increase wear rate,

I am concerned about wear rate, but due to a lack of lubrication, not 
due to overheating.

> and at worst cause a local siezure, possibly with the
> result of dropping a valve guide.

I'm not sure why a seized valve stem would cause a dropped valve 
seat, but I'm not sure it would matter -- if the valve stem seizes, 
you're probably in for major work anyway, dropping a seat wouldn't 
add signficantly to the workload.

> If I was to contemplate doing this on either the AJ6, or any of the V12
> variants, I would be looking very carefully at the actual valve
> composition, and the engineering profile.

I was wondering if Teflon valve stem seals wouldn't be more suitable 
with sintered bronze valve guides than the sintered iron guides in 
the Jag, but mainly from a lubrication standpoint, not heating.

> Without research, I'm not sure of the type of valves fitted, but would be
> looking for sodium filled, and stellite faced valves.

If you find EITHER to fit the Jag, let's hear about it!

> I would consider
> teflon on input valves.

That is an option.  The question of nitrile vs. Teflon is one thing, 
12 places vs. 24 is another.

> Before any of you actually undertake this process, I strongly recommend
> that you contact either AJ enginnering...

Have already forwarded Bywater's response.  So far, his opinion seems 
to be more of a "why bother?" type of thing rather than pointing out 
some sort of real problem with using Teflon seals.

> The original nitrile seals do wear, and are known to be a problem...

Is this true?  I couldn't say for sure when responding to Bywater.

> and they
> also get brittle, again overheating?

My car apparently overheated, since I dropped a valve seat.  But my 
nitrile seals were NOT brittle -- one of the few types of rubber 
parts from my car that weren't.  It's either fairly cool within the 
valve train area, or the Mobil 1 helps keep the nitrile pliable.

> As the temperatures in the USA are very high this year, I would also try
> and find out what specs Jag used on engines shipped to the middle east..
> Probably lower compression ratios, different radiators, high capacity water
> pumps etc etc....

Who's taking bets?  My money is that the engines are EXACTLY the same 
as anywhere else with a similar lack of environmental regulations.  
In fact, I'll even bet that the MidEast cars didn't get the full flow 
oil cooling that Germany had until everyone else got it.

 -- Kirbert      |     If anything is to be accomplished,
                 |     some rules must be broken.
                 |          - Palm's Postulate

---

Follow-Ups:

• Re: [xj-s] Valve Stem Seals
• From: John Napoli <jgn@li.net>

References:

• Re: [xj-s] Valve Stem Seals
• From: "David Low" <dkl@lbwf.gov.uk>

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