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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,224
Exhaust valve guides and valve stems wear out faster in a 930 engine than any other production engine I've seen or experienced.
They are usually somewhat worn beyond spec in 30,000 miles from new and just keep getting worse.

It's because of extreme intense localized heat in the cylinder head of a turbocharged air cooled engine and because the exhaust valve and guide is downstream from the intake valve in the cooling air and upside down at an angle and has a tight fitting valve seal so very little oil ever migrates up the valve stem against gravity and the tight fitting valve stem seal while the engine is running and lubricates it and the valve guide.

Hate to say it but that part of the 911 engine design really sucks in my opinion.

Some 935 exhaust valve guides had little cooling fins at the top to increase surface area to help cool them as oil splashed onto them.... maybe they all should.

If you have oil in the turbo compressor housing, charge pipe, and intercooler the turbo seals are probably worn and leaking to some degree. Make sure the air filter is clean. If there's also oil in the turbine housing or hot side than it definately needs to be rebuilt.

If oil is in the air cleaner housing and all over the CIS air flow sensor plate the piston rings are probably worn and letting some exhaust gasses blowby into the case pressurizing it a small amount.
Then the blowby gasses and oil mist goes to the oil tank through the breather hose where it eventually gets routed back to the air cleaner housing.

You need to do a leakdown test with leakdown gauges, and then your ears and a hose in the right places while filling the cylinders with around 100psi air pressure to diagnose the condition of the rings and valves at TDC.
Old 12-29-2009, 09:12 AM
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