Eric_Oz_S2

So what's the consensus on how long the valve stem seals or valve oil seals last? It seems that I have oil leaking past the guides as evidenced by black oily soot on the top of the pistons as seen through a borescope. Spark plugs have a brown ash buildup as well, although this could be due to running relatively rich for my supercharged setup.

Is it worth changing the oil seals without the stem seals if there is not too much "wiggle" in the valves? I presume the oil seals crack and harden over time leading to ineffective sealing.

Looks like I may be in for a head job

Thom

What do you call "valve oil seals"?
The only oil seals in the head I'm aware off are the valve stem seals.

I would have everything replaced while the head is off, valve springs included. On the 16V head they are notorious for breaking and setting their preload is quite a hassle.

Eric_Oz_S2

Yep - valve stem seals.

What is the go with setting preload in the springs? Haven't heard of them breaking on the S2 before - but then again I have really looked around either.

Thom

Broken valve springs do not seem to occur very often on 16V heads but it happened on my S2 and I heard it happen enough times to have come to think that valve springs on a 16V head should be better replaced after 200k km (120k miles).
When it happened to me last year the inner (small) valve spring broke, then the valve floated somehow and got hit by the piston. The engine ran like it was misfiring and I kept chasing for an ignition issue until I removed the head cover and figured it out.

kev951

valve stem seals can last a lot longer than the bronze valve guides which is the first place you lose power in the cylinder head. if your cylinder head has over 20k on it, I can pretty much guarantee you already have some leakage throught the valve guides. Its a good rule to change the guides and stem seals any time the head is off, unless you just had it refreshed and it has low mileage on it. Stem seals actually wear out faster when they are dry. so the car that has been sitting for three years and gets started up once is a good example of dry stem seals.

Eric_Oz_S2

I suspect at 160,000 km with lots of track time, that my head is indeed due for a refresh. My suspicion is that oil is being sucked into the cylinders through the valve guides on sudden closed throttle (vacuum) on the track.

Is valve guide replacement a DIY job? As I understand it valve guides are available only as oversize which requires the holes to be reamed slightly. Springs would be easy.

V2Rocket

Valve guides are $5 new, and I got an NA head rebuilt at a local shop and they charged $5/each to install new guides...cheap insurance.