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1985 Porsche 928s
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Carbon in the intake
Upon disassembling my 1985 32v engine (with 65k miles) I notice that there's quite a lot of crusty carbon / soot on the inside of the intake tubes around where the fuel injector is inserted. This extends a few inches up into the intake tubes. Is this normal? Does it maybe indicate a valve wear / timing issue? I plan to do a leak-down test but was curious to know if this was expected.
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01-17-2013, 11:53 AM
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Join Date: Aug 2012
Location: Philadelphia Area
Posts: 3,680
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I replaced my plugs last weekend and looking down in at the pistons i saw a decent amount of carbon deposit, plugs looked normal. I also have 65k miles. If you had pre mature valve wear you'd see it out back. I think that is normal but should be cleaned.
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Matt Mariani @the_r_institute Authorized Retailer FIKSE Wheels Mod Italian Wheels Maxilite classic wheels Last edited by The Fixer; 01-17-2013 at 12:38 PM.. |
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01-17-2013, 12:31 PM
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1985 Porsche 928s
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OK, thanks Fixer. I'll see what it looks like once I dig a little deeper. I had planned to do a lot more with the engine removed but I might scale it back a bit so I can have it on the road for summer.
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01-17-2013, 02:28 PM
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Join Date: Aug 2012
Location: Philadelphia Area
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Why are you taking it apart?
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Matt Mariani @the_r_institute Authorized Retailer FIKSE Wheels Mod Italian Wheels Maxilite classic wheels |
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01-17-2013, 02:43 PM
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1985 Porsche 928s
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Quote:
The car is in great shape (2 owners) but the history is a bit patchy. The Porsche garage who inspected it said it was in great shape and ran well. The TB and WP are a given and I'll replace both head gaskets and oil pan seal at the same time, plus have a good old look around while I'm about it. |
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01-17-2013, 02:52 PM
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Join Date: Aug 2012
Location: Philadelphia Area
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Didn't know, guess you should have the heads and valves looked over by a machine shop anyway.
Do you know why the head gasket went? I would wonder if it had anything to do with the head studs. There is probably some good threads to read on the head studs/bolts I'd make sure that is right.
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Matt Mariani @the_r_institute Authorized Retailer FIKSE Wheels Mod Italian Wheels Maxilite classic wheels |
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01-17-2013, 03:19 PM
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1985 Porsche 928s
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The PDI mechanic diagnosed head gasket due to a small pool of oil under the car after it was run for 20 minutes. What I did find, though, was quite a pool of oil in the "valley" - between the banks, possibly due (I think) to the breather from the RHS crank cover to the oil filler having completely disintegrated.
I have read some interesting threads on head bolts - a little apprehensive now. |
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01-17-2013, 04:45 PM
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Join Date: Jan 2007
Location: SoCal
Posts: 10,349
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I think I would always want new guides and seals if the heads come off.
AFAIK oil is almost never the issue with 928 head gaskets, always the coolant. |
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01-18-2013, 12:06 AM
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1985 Porsche 928s
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Quote:
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01-18-2013, 07:52 AM
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inventor
Join Date: Jun 2007
Posts: 136
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Most likely a bad rear cam seal...
Carbon on the last few inches of the intake runners is normal. It's fuel (reversion) mixed with oil vapor (PCV) which is then baked on. Clean/grind it out. Gasket match while you are at it. Will give a few more HP. (Leave a slightly rough surface.)  
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01-18-2013, 08:50 AM
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