burgass

Hello
Could some one help with diagnosing the following?
During a DE my engine suddenly started sounding as if a spark plug has been blown and lost power.
After inspection it was discovered that cylinder 6 seems to be blown on the outside towards the front end of the car. There is a small buckle on the outside of the heat shield exactly inline with where the top end connects to the cylinder block. You can feel compressed warm air coming from that area.
The engine has been repaired only 10 000km ago for oil leak between the top end and cyl. head. I am not sure what was the extent of the repair but the P-Car shop claims the machined the surfaces and made a detailed inspection.
The most amazing fact is that the same P- Car shop checked the compression of the same cylinder just one day before it blew up and told me that it was perfectly OK. Last but not least – I did not miss gear during the DE which directly excludes any damage caused by driver error.
Does anybody have any suggestions? The shop says “it could be anything” but they totally exclude any mistakes which could have happened during the last repair by them
Thanks in advance!
Regards

PS
Here is a pic just to ilustrate which heat shield I mean

Jeff Curtis

Burgass, I'd bet that your distributor belt is broken, or head studs...seen it a couple times, got the pics, seen the bills - thank GOD not mine!

Check the distributor belt before anything, then drain the oil and remove the lower valve covers to see if any of your head studs have snapped, evident by the barrel nuts and broken piece of stud laying in the galley between your heads and case.

Let us know what you guys find.

burgass

Thanks Jeff! I will do exactly as you said. By the way I heard another idea - due to bad machining and fittment of the top end and cyl. block an existing small "gap" has widened and finally turned in to a whole. Does that make any sense?
Regards

Jeff Curtis

Burgass, if the shop took your ORIGINAL cylinders and machined them for a head gasket, then the outer walls would be pretty thin...thus a possible problem...I would be more concerned if the inner walls were made too thin to accomodate the groove at the top of the cylinder, where it mates to the head.

Just to make myself clear, 1989-early 1991 cylinders were not made to accomodate a gasket - one cannot have them modified to Porsche spec for a head gasket...although it's possible a custom application could work??

I went through all of this when I updated my 1991 motor to late specs with head gaskets, etc. The earlier heads can easily be modified to accept a head gasket, it's just a simple flycut on a lathe or a milling machine, but the cylinders MUST be updated.

I wound up buying a good used cylinder/piston set from Dave K. (from a 1993 RSA, I believe) and didn't realize that my original heads would be okay until I had purchased a late set from another Rennlister in California...that's why you saw my original heads up for sale for sooooo long!

My original pistons/cylinders sold fairly quickly, to a local who is working on a "freak" 914 project.

Back to my original theory...and I'll put a wager on this...broken head studs or dizzy belt, with a broken headstud, you get the rattling and "clicking" sound from massive cylinder leakage to the atmosphere, with broken dizzy belt, it's possible the rotor got stuck on cylinder 6 and burned a hole in it because it sparked there for every pulse of your distributor, all SIX pulses per every other revolution of your engine.

darth

Hi Burgass

I don't quite understand where they did the machining. There are 2 places where 2 surfaces meet - head to cylinder and cylinder to block. I suspect they machined the head to cylinder surface reinforced by what you said, that the heatshield has a small buckle which is directly inline with the head to cylinder surfaces. Did they machine just one cylinder? I hope not - oterwise they would have to compensate for the material remove in order to maintain the head alignment. I'm not sure how a broken distributor belt would have anything to do with your problem but a broken head stud is definitely a possibility and likely you've lost a seal at the head to cylinder surface because of this or the machining wasn't done correctly. I can't imagine this is a coincidence that the cylinder to head seal "let go" after it was machined!

Sorry - but hope this helps
Bill

burgass

Jeff, as I understood the only surfaces which were machined were where the top end meets the head. Nothing about head gasket or modification. "MASSIVE cyl. leakage - thats what it sounded like. I hade a lose spark plug on my other car that gave the same sound. But no rattling and "clicking". I would not be suprised if it turns out to be a head stud.

burgass

Bil, they said they machined all cylinder both left and right side. Either the machining was no good or they did not apply enough torque on the stud I guess. They told me that they checked the studs and found them OK.

darth

Burgass

There is no sense trying to guess what is broken either you or the shop will have to physically investigate - fact is you're lossing compression and you shouldn't run the engine because the fuel going into that bad cylinder isn't being burnt and will be washing down the cylinder wall of any lubrication.

Let us know what you find
Bill
90C2