Hi Everyone,

I've got a 1986.5 4.7 928 S2.

I've taken the heads off due to a blown head gasket. I'm about to send them off to be re-conditioned and have been advised by an engine-builder friend of mine to replace the valves as a matter of course. Seems like a good idea after nearly 40 years and 130k miles.

So looking at the options, it seems I can either spend about £20 a valve for non-Porsche ones, or about £230 a valve for the OE ones. I don't really want to splash out £2k on the Porsche ones, but then £20 each makes me nervous about the quality of the non-Porsche ones?

Has anyone out there used the cheap ones? Did they work, or did they crumble and destroy your engine after a week? Should I just get the old ones cleaned up? - they look ok, no obvious damage or excessive wear.

Thanks in advance for any advice..

Andy

 

Unless your engine builder friend of yours has determined that the valves are worn out, his advise is terrible. This is not a race engine where components are lifed. Disassemble the heads, measure the stems - dimensions are in the WSM and proceed from there.

Your heads would most definitely need exhaust valve guides, which would be worn beyond specification due to the relatively heavy valves, short valve guides and relatively large lift on the S2, but normally that would be about it...

 

I'll take the old ones,where do I send shipping money to??

 

I'd guess that your machinist was talking about replacing the exhaust valves and somehow that conversation got confused.
The intake valves, unless stem wear or margin wear becomes an issue should be 300,000+ mile pieces.

Conversely, the exhaust valves live a life in hellish temperatures and frequently need replacement at the 1st rebuild.
And, there's quite a difference between Factory exhaust valves and aftermarket "cheap" exhaust valves.
The factory exhaust valves are sodium filled to transfer some of the heat from the head of the valve to the stem. The "cheap" aftermarket exhaust valves appear to be sodium filled, from the outside, but have no sodium inside.

Factory exhaust valves are very superior!

 

Thanks for all your replies. Looks like I need to spend my money on a good micrometer...

 

At Rose Passion a Porsche exhaust valve cost 48 €

 

Guessing not a factory one, with sodium.

I've got 4 "aftermarket" listings for "aftermarket" exhaust valves, from 3 different parts suppliers.
They range from $14.60, $24.31, $24.78 and $46.00.
I've sectioned 3 of those valves, looking for any trace of sodium. Nothing. (Didn't bother with the $14.60 one.)

Porsche didn't put those steel sleeves in the S2 exhaust ports because they were bored.
The exhaust temps were so high that they were melting the aluminum ports....

 

Interesting!
An ugly trap for the uninformed, thank you Greg!

 

The price delta was so severe that it warranted investigation. I've had previous issues with valves and needed to know the truth.

 

So the cheapest original 92810541004 are 145 €, if available.
Is the exhaust valve in the 944 engines even more stressed than in the S engines?

 

Correct.
I believe that a late Euro S engine uses a 928 195 409 02 intake and a 928 105 410 04 exhaust.
And no, I believe that only in the 951 engines that this would be an issue.
(They are also sodium filled.)

 

I visit Jochen this evening and he told me Porsche invented the sodium filled valves in the 951 engines for the public cars.
Jochen is pissed off because he can't also get oversized pistons for early and late 928 engines.