Valve stem seals

ivath · ivath's Garage

My Carrera 3.2 is starting to use a bit too much oil. Based on leak-down results I think the oil is entering the combustion chamber through the valve guides. Bad valve guides seems to be a problem on the 3.2 engines (from what i've read in books and on a lot of forums). I have owned other cars that have started to smoke and use oil and I have then installed new valve stem seals and the problem have been solved. This has been done with the engine in the car and by pressurising the cylinder through the plug hole. Have somebody tried to only change the seals on the Carrera with the engine in the car?

I think it should be possible at least on the exhaust side. The rocker shafts should be possible to remove and then the valve springs can be removed. Then it is also much easier to check the play in the valve guides.

I'm tempted to try this before I go for a top-end rebuild.

Ivar

rvanderpyl · rvanderpyl's Garage

That might work for a short period of time, however the real issue is that the valve guides are worn, which allows to much oil past the valve stems, and also allows the valve to 'rock' in the stem. This can cause accelerated wear on the valve seats and even lead to bent valve stems/broken off heads if it gets too bad. So what you are doing by just replacing valve seals is ignoring the real issue which can come back and bite you in a major way.

ivath · ivath's Garage

I have always thought the barrier/sealing component was the stem seal it self and not the fit between the valve and valve guide(?). But I can understand that the seal are more prone to fail if the valve "rock" in the guides. It seems that the 911 is more prone to valve guide wear than many other cars which suffer from problems with the seals prior to shot valve guides.

88911coupe · 07-05-2006, 07:52 AM

I guess the question is still whether or not you can replace the valve stem seals with the engine in the car. Is the only way (without disassmbling the engine) to check whether the valve stems are worn is by seeing how much the stems move while in place? I would think that at least some engines burning too much oil may in fact just have hardened seals...or is that wishful thinking?