Dave928S

I used genuine Porsche guides, and the shop that I mentioned in post #6 fitted them, and did all the other work on the heads.

Mine were reamed out to a shell before removing them, to prevent galling of the bore, the new ones machined to give the correct interference fit, pressed in using differential head/guide temperatures to prevent galling, and then reamed to the correct internal dimension concentric with the valve seat.

A good specialist shop should know exactly what to do.

GB was correct in advising that the factory limit is excessive. Mine were within wear tolerances, but allowing oil past.

GregBBRD

Like you could fit two valves into the same guide?

Like I said......middle of the Sahara...only way out....use a guide and valve with .5mm clearance. You will get out.

Replace the guides, when you do get out.

.8mm clearance....start walking.

Dave928S

Yep ...super slop.

It was well within the wear WSM limit, but way over that which I'd regarded as excessive on lots of other road and race motors I've built and rebuilt, and well outside what I regarded at the time as OK.

Your thinking confirmed what my gut feeling was, and the views of the shop that did the head work, which is why I posted this thread questioning the Porsche wisdom ... relatively short guides and therefore more prone to side rock and bell-mouthing/ovalling of the bore, too worn, were going to get worse ... needed replacement.

Vilhuer

Greg will not approve I'm sure but some people have successfully used thin wall bronze liners like K-line to fix clearance.

Dave928S

I'd like to hear his views. I personally would still go down the path of new guides, as there's not a lot of difference in the set up and machining work required.

Vilhuer

Cost in here at least is much smaller. Talking something like 1/3 or 1/4. When done right they seem to hold up. When something goes wrong they can start to move which obviously isn't good.