Valve Stem Seals

[blind_elk]

I've been having a bit of trouble since my engine rebuild, losing (burning) oil. My "tame mechanic" thinks it is a problem with the valve stem seals, although they were supposed to have been replaced at the time.

He has been asking around about various things related to fixing the problem. One place told him that there is a problem with the seals and boost levels - anything above 15psi and the pressure escapes up the valve guide and blows the seal off the top of the valve. When the engine is opened up, you find the seals just lying around beside the valve.

Anyone have any experience of this? Is it BS?

Tx.

[madbung]

The valve guides would have to be loose as a whores... for that to happen.

Valve stem seals stop oil running back down the valve stem into the cylinder when the engine is static...nothing more.

When the valve stem seals are gone you get smoke on start up after you've been parked a while then it burns off with no smoke/oil loss during operation.

If what your person says is true...he seems to think it's forcing it way up the valve stem/guide instead of taking the easy/designed route through the exhaust outlet in the head, that really doesn't make sense. If it were you'd effectively be making positive pressure (compression) through the head and into the crank...dipstick blowing out?

It could well be a burnt out/poorly seated valve or 2...but It won't be valve stem seals.

If anyone ever looks at a car thats blowing smoke under acceleration/de-accelleration and the owner says it's valve stem seals, have giggle then walk away. It's the oldest trick in the book.

Edited June 25, 2008 by madbung

[blind_elk]

Then what causes the oil burn during / after extended periods of idling? Where else should I be looking?

[madbung]

Oil seal leaking/weeping turbo side perhaps.

If you ever see a valve stem seal, it's like a small rubber cup that goes around the valve stem with the cup facing down. This basically redirects oil away from the valve stem/guides...kinda like an umberella and handle in simple terms. They don't hold compession or seal anything really.

As for his too much boost theory...you know plenty of people on here that run high levels of boost with no problems.

Ever heard of a high performance valve stem seal? me either

You might want to have someone else look at the car.

Edited June 25, 2008 by madbung

[blind_elk]

Yes, I know what a seal looks like. And yes, I'm aware of many members running ridiculous boost numbers without any reported seal problems. It's not my mechanic promoting the theory, it's another "head expert".

Actually, I recall hearing that turbos supplied by the guy who built mine almost invariably leak oil. Maybe time for a good aftermarket unit.

Would forged pistons have any effect - my theory being the piston cools and shrinks during prolonged idle, and oil doesn't get scraped away properly from the cylinder wall?

[madbung]

Pistons no....it's the rings that perform that task.

Some setups are designed to let some oil through, generally for big hp apps or unleaded conversions.

Edited June 25, 2008 by madbung

[_x_FiReStOrM_x_]

Most forged piston applications will consume a bit of oil, as the forged units take longer to thermally expand, and expand more than a cast piston... therefore they require greater bore clearance to allow for this; although the consumption shouldnt be overly noticeable.

If you're losing a fair bit of oil and its not leaking externally, as madbung said, check turbo seals.. if they checkout ok and you're still in doubt, have your mechanic perform a leakdown test just for peace of mind.

Edited June 28, 2008 by _x_FiReStOrM_x_

[Godzilla32]

Inlet valve guides will cause oil to be burnt if there is too much clearance. The vacuum of the intake stroke will suck oil down the guide and be burnt.