944cer Posted August 19, 2007 Share Posted August 19, 2007 I had an overheating and oil issues my last time on the track, 1st for car as a race car, causing rod bearings to go out. So I'm beginning the process of pulling the engine to replace bearings and have the head reworked. I ran a compression check and came up with the following; #1 132, #2 120, #3 110 and #4 125 psi. Any thoughts on the results? Seems like a lot of variability to me. I am also wondering if the low numbers could be a result of slighly warped head from overheating or is it something more major? Rings? TIA Lee Quote Link to comment Share on other sites More sharing options...
Weston Posted August 19, 2007 Share Posted August 19, 2007 That is a bit of varience, but on my previous track car, I found that a dead rod bearing can contribute to lower compression readings on that cylinder, so that may be part of the issue. It's usually #2 that sees the most wear, with #3 being close behind it, but that's not set in stone. Quote Link to comment Share on other sites More sharing options...
944cer Posted August 19, 2007 Author Share Posted August 19, 2007 It is my understanding that 2&3 do get the most wear as well. However I can't see how those bearings would affect compression. Quote Link to comment Share on other sites More sharing options...
944cer Posted August 19, 2007 Author Share Posted August 19, 2007 I just checked the dip stick again; hmmm this time its goo. So the oil and coolant have definatly mixed. Head gasket and/or oil cooler ring. Quote Link to comment Share on other sites More sharing options...
Weston Posted August 20, 2007 Share Posted August 20, 2007 It is my understanding that 2&3 do get the most wear as well. However I can't see how those bearings would affect compression. When there's a gap between the crank and the rod, the piston wont get pushed all of the way up or pulled all of the way down, so the compression will be a little lower on that cylinder. I saw a good 20-30 psi drop when I completely lost the rod bearing on my old Integra. I just checked the dip stick again; hmmm this time its goo. So the oil and coolant have definatly mixed. Head gasket and/or oil cooler ring. While the compression test does make the head gasket a suspect, I'd suggest doing the oil cooler gasket first (be sure to get an alignment tool for that). We tore apart Chuck's motor and replaced a perfectly good head gasket, only to find that it was just the oil cooler gasket leaking. It will take some time to get rid of the milkshake in the coolant and oil, and it's pretty bad for the bearings... I'd flush both the coolant and the oil twice if it happened to my car. Quote Link to comment Share on other sites More sharing options...
Chuck T. Posted August 20, 2007 Share Posted August 20, 2007 i had to drive the milshake for too long and it trashed the bearings. Quote Link to comment Share on other sites More sharing options...
944-Spec#94 Posted August 20, 2007 Share Posted August 20, 2007 You probably should do both. I have seen plenty of old stock headgasket fail due to age more than anything else. My head gasket was replaced long before failing yet it was in sad shape. Corrosion had even created some holes in the head. Gasket failure was just a mater of time. So I had the holes in the head welded up and new gasket installed. Plus pulling the head will get you a chance to see if you have ring issues. If you are going to race the car it will be well worth it. If you are just going to street drive the try to get away with just oil cooler seals. Quote Link to comment Share on other sites More sharing options...
944cer Posted August 22, 2007 Author Share Posted August 22, 2007 Thanks for the info guys. Alignment tool for the o-rings? Guess I'll have to get one. Quote Link to comment Share on other sites More sharing options...
Tim Comeau Posted August 22, 2007 Share Posted August 22, 2007 You can use the oil pressure relief valve itself to align the oil cooler. Just carefully slide it in and out as you torque the 13mm head bolts sequentially. It should still slide in and out when you're done tightening the cooler down, i.e., no binding. Quote Link to comment Share on other sites More sharing options...
944cer Posted August 22, 2007 Author Share Posted August 22, 2007 Thanks Quote Link to comment Share on other sites More sharing options...
dartydave Posted August 23, 2007 Share Posted August 23, 2007 throwing oil filled with rod bearing around can score your cylinder walls and cause compression loss past the rings. Do inspect the cylinder walls. A leakdown test will give you a better idea of where your problems are. Quote Link to comment Share on other sites More sharing options...
944cer Posted September 13, 2007 Author Share Posted September 13, 2007 The engine is completly disassembled, down to just the block. The crankshaft and heads are off to the machine shop. I have read about having the oil journals on the rod bearings on the #2&3 cylinders modified. My question is what are the specifics of the modification and is it advised and class legal. It should be easy to have done since it is already in the shop. Quote Link to comment Share on other sites More sharing options...
944-Spec#94 Posted September 13, 2007 Share Posted September 13, 2007 My question is what are the specifics of the modification and is it advised and class legal.It should be easy to have done since it is already in the shop. Cross drill #2 & #3 rod journal to the same hole as exisiting just 180 degrees around. It is legal as it only improves reliability, but not peformance. Quote Link to comment Share on other sites More sharing options...
944cer Posted September 13, 2007 Author Share Posted September 13, 2007 Thanks Joe. Quote Link to comment Share on other sites More sharing options...
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