Sticky Valve?

[WydRyd]

Curious, what's the fix for a sticky valve?

I performed a "cold" compression test on my motor last night and found the following results:-

# 1 = ~100
# 2 = ~110-115
# 3 = ~110
# 4 = ~110-115
# 5 = ~110-115
# 6 = ~110-115

All results look OK for a low compression 3.3 Turbo motor, HOWEVER, Cyl # 1 has me a little concerned.

Whilst doing the test on that cylinder, the needle on the gauge didn't advance normally (like the others). It eventually climbed to ~100 - 102 psi after several strokes.

I've read that this is typical of a sticky valve condition.

IF I have a sticky valve on Cyl # 1, what's the typical fix for this?

I have the symptoms I guess (low idle 300-400rpm's, stalling, popping/back-firing on decel, power loss etc).

Advice/suggestions?

EDIT: I know a leakdown test is the best test for determining the cause of a suspect cylinder, but I don't have access to a leakdown tester and air compressor at the moment.

[WydRyd]

I've read that Marvel Mystery Oil can be used as an oil additive to lubricate the valve-train and loosen any sticky valves.

Anyone tried this stuff?

[WydRyd]

Anyone???

[Early_S_Man]

Merv,

I don't think there can be such a thing as a 'sticking valve' in 911 engines.

The term 'sticking valve lifter,' as in engines with hydraulic tappets ... could have been shortened in the imprecise world of urban myth and old wives tails ... to 'sticking valve' and it is technically still correct, if you mean the valve within a hydraulic tappet or 'lifter' ...

But, I submit that the concept doesn't fly with respect to the 911 valve train ... primarily, because of the generous amount of oil that flows down the valve guides in regular engine operation.

I have used Marvel Mystery Oil in the gas tank from time to time ... but it was for the health of the injectors and fuel-handling apparatus, not for the valve train!

ps ...

The cold compression check is notorious for not giving good or representative results ... adding oil can be useful for diagnosing engines with significant wear problems, but I suspect a Turbo would be doing serious mosquito-fogging [oil burning] by the time that kind of wear produces a difference in dry/wet cold compression tests!

[Zeke]

If you must do a cold compression check, you can squirt a small amount of light oil (like the MMO) in the cyls and move it around with some air from a nozzle or the straw they provide with those little cans of compressed air. This will put a light coating on the walls of the cyls (not guaranteed to get perfectly even distibution) and seal the rings better so you can concentrate on listening to the valves. Maybe you can think of something that comes in a can and do it all in one step.

But, a valve would not seem to "hang" open at cranking speed, if that's what you mean by sticking. If it does, you shouldn't even run the engine, IMHO.

[Jandrews]

Warren,

Please tell us more about the MMO in the gas tank for the benefit of injectors and fuel delivery system!

Thanks,

JA

[WydRyd]

Thanks for the input guys.

Yes, please elaborate on the benefits of running MMO in the gas tank.

[WydRyd]

If the compression is lower on that one cylinder, then perhaps I have a blown out head gasket? Damn I wish had a leakdown tester

[Adam]

It could be a "tight" valve, one that doesn't quite close properly, allowing a leak - my 2.7 had a significant loss of compression on one cylinder and after a thorough valve adjustment, I got it all back.

[PatrickB]

Never used in my cars, however, I used to run MMO in my last 2 airplanes with great results! Excellent for top cylinder lubrication when added to the fuel tank. About 9 years ago, they started changing the formulation of AVgas, as well as virtually eliminating 80LL fuel. The latter had a high lead content, that was essential to smaller bore motors for top cylinder lubrication. After the fuel change, premature valve failure was rampant in smaller bore motors. Unfortunately, I had to find out the hard way with an engine out at 7000' at night above a cloud bank....