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[Guest]

From: Rob D
Email: robdumoulin@yahoo.com
Date: 30 Jun 2001
Time: 11:19:00

WHAT SHOULD I DO? I just ran a compression check on my 931 and got 143, 130, 141, 141 PSI. I added oil to the #2 chamber and got 151 PSI. The test was done shortly after the engine idled about 5 minutes, so it was not fully warmed up. The car oil smokes badly at idle and when you let off the gas. The plugs are not oily, but do have carbon on them. What is the acceptable PSI compression for this engine? I suspect 140 is ok, but is 130 PSI acceptable or does it mean the engine needs a rebuild?

[Guest]

From: MAS
Email: mashwoodsmith@hotmail.com
Date: 30 Jun 2001
Time: 13:20:04

I've got no idea what is normal for a 931, but my 87 924S when tested three months ago was:

170, 175, 170, 175

-MAS

[Guest]

From: Colin I
Email: colin@cingram.demo.co.uk
Date: 01 Jul 2001
Time: 04:51:55

Rob,

are you unhappy with the oil consumption, so think the engine's worn out? the official "acceptable" oil consumption is 1.5 litres / 1000 km ( ie quite a lot!)

official workshop manual says acceptable compression range is 8 to 11 bar ( 118psi to 162 psi ) with a max difference between cylinders of 3 bar ( 44 psi ) - yours sounds ok. remember, turbos have a low compression ratio which, with boost, takes it up to an effectively high compression when operating. you only see low pressures when doing a cranking compression test, so don't compare the number you get with friend's naturally aspirated motors.

you should really do the test with a hot engine ( difficult working on it, though!)

if you're seeing oil smoke, don't just think it's the rings - it could be the valve guides & seals ( a notorious problem area ) or, unfortunately, the turbo itself. if you take the turbo transfer tube ( the one that goes to the throttle housing) off and look inside, you may well find it heavily contaminated with oil.

this is being puuled through the turbo seals when you close the throttle. there are several reasons for this - the seals worn, the pop-off valve in the turbo not operating freely, or the closed crankcase breather (ccb) not operating properly. there have been several changes to this over the model run of the turbo, and it's easy enough to investigate and correct - basically, keep it clean by washing it out in a suitable solvent, and make sure all the hoses are clean and free flowing.

you can actually dismantle the pop-off in situ on the car to check it, but it's still a difficult job ( albeit easier than taking out the engine!) you can hear it working by snapping the throttle open a closed around idle - you hear the valve "clacking" as it hits the stops.

a turbo full rebuild is expensive - typically $750 in the US , 450 pounds in the UK and you've got to get the turbo off - some people find it's easier to take it off with the cyl head , as the bolts can seize solid and you can't access them. a turbo rebuild kit is cheaper , but you need to be a good mechanic to do it yourself.

hope that's usefull

colin

[Guest]

From: Rob D
Email: robdumoulin@yahoo.com
Date: 02 Jul 2001
Time: 09:30:08

Thanks for the info Colin. The performance of the car is still great, but the very substantial smoke screen it is producing is not acceptable. I am trying to isolate the problem to either rings, valves, or turbo prior to doing a complete overhaul. I don't want to waste time and money rebuilding the turbo if the engine and valvetrain are shot.

[Guest]

From: larso
Email: l_porsche@hotmail.com
Date: 02 Jul 2001
Time: 13:20:35

what does the exhaust smell like, and exactly how much consumption of oil are you getting, and have you checked the table spoon of oil rule in the intake ducting

[Guest]

From: Rob D
Email: robdumoulin@yahoo.com
Date: 06 Jul 2001
Time: 13:31:18

The smoke smells like oil. The consumption I am not able to determine because the car smokes too much to drive. There is little or no oil in the throttle body.