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WERK I WERK I is offline
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Join Date: Jan 2003
Location: Wisconsin
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Quote:
Originally Posted by copbait73 View Post
Iím not a CSI investigator but I have extensive background in turbos and tend to get unhinged when every engine problem on a turbocharged engine eventually gets blamed on the turbocharger.
Well, get unhinged because this camshaft failure was due coking in the turbocharger.

Quote:
Originally Posted by copbait73 View Post
The thread starts with describing an extreme thermal excursion for the entire engine. Now in this situation the turbo is happily idling away and not exposed to conditions to form varnish much less hard coke. However being an air-cooled engine if the oil is at an excessive temperature so are the head temperatures.
So you are telling me that the ambient temperature of a turbo bearing shaft "happily idling away" is lower than the oil (230 degrees) that's being circulated in this situation? Remember, the reason for the elevated temps in the engine oil is due to the volume of oil being circulated through the engine is insufficient. Same applies for the turbocharger. Varnish is going to generated on the turbocharger shaft in a condition such as this with dino oil.


Quote:
Originally Posted by copbait73 View Post
Everyone who has experience with non turboed air-cooled Porsches, aircraft or the lowly VW knows you will find coke chunks in the oil strainers. Without turbos, how can this be?
Who said it can't?

Quote:
Originally Posted by copbait73 View Post
Because they are air-cooled and the coke is being formed in the extreme temperature areas localized around the exhaust valves and moving outward as the mineral based oils are being cooked. There is also the very real problem of all turboed engines; blow by. This forms similar accumulations in the vent hoses, oil tank, etc.
The used oil delivered by the DRY SUMP PUMP is returned to the OIL FILTER before going into the holding tank. So anything gathered from the engine's sump is going to be filtered before residing in the holding tank. The turbo sump pump is another matter all together.

Coke doesn't just magically appear. Elevated oil temps go through a metamorphosis. The coke chunks I found in the valve train feed tubes had hardened over time and the exposure to brake cleaner which I tried to use to clear the tubes (didn't work). Also, the appearance of the "chunks" looks like they attached themselves to each other over time. Before becoming coke, oil becomes a very tacky substance and I am sure that is how the pieces became attracted.

Quote:
Originally Posted by copbait73 View Post
I pose one more question for you. If these chunks shown in the initial posting were formed in the turbo bearings, how did they get through TWO close tolerance pumps, the oil scavenge then the oil pressure pump without being pulverized?
Like I said, The coke did not have to appear immediately on the turbo shaft, but the metamorphosis of oil to varnish to tar will easily get through the turbo sump pump.

Quote:
Originally Posted by copbait73 View Post
I think these were formed in the cooling rail oil delivery path during repeated running and hot shutdown extremes throughout the life of this motor. This last extreme was the killer.
This was a split case freshly rebuilt engine (about 3K miles since rebuild), thoroughly cleaned... I blame the failure on two factors. Web Cams would not warranty the cams if Syn Oil was used to lubricate the engine, so I had to use dino oil. Two, the current dino motor oils are lacking in the proper minerals for the early engines running this type of valve train mechanism.
I did not shut the engine down hot. The engine was shut down after driving it at highway speeds to bring the temps down.


Quote:
Originally Posted by copbait73 View Post
If you canít except coke, obvious you canít, use synthetic oil, as do all the gas turbines in the world.
Marty
The reason we (or I) can not accept the coke is obvious. It was a poor design on Porsche's behalf to have used oil returning from the turbocharger to the main sump tank UNFILTERED.
Two, it is a poor design to have the top end lubricating system OPEN LOOP. Once a particle such as coke gets in there, it's just a matter of time before it gets into the feed hole and begins to clog it.
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'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 12-09-2007, 05:32 AM
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