Well yesterday I did a compression / leakdown test as I have been burning a little bit more oil then I would like. First off the engine wasn't cold or hot either , it had been driven for a good 40 minutes and then sat for a good hour before starting the test. Only a dry test was performed and the results from cylinder 1-4 were 145,165,165,165. So we rotated the engine to bring cylinder 1 to tdc and did a leakdown and was getting about 9%. We didn't do the others as the compression seemed fine in those. Now we determined it was head related as there was no hissing at oil cap or dipstick, so I hope this rules out rings if though I plan on building my engine soon. The last time the compression was checked it was back in February and the results were 162,165,165,165. We checked cylinder 1 then and it had about 2% leakdown. It was brought to my attention at that time no that I remember that there was some oil residue in cylinder #1 exhaust port. I remember seeing it when the exhaust manifold was off, just thought it was from the bad valve seals there were just being replaced so didn't think much about it. I'm being told now that its probably my exhaust valve guides that are shot and thats why I'm burning oil. I had a issue before with burning oil when I had a couple valve seals pop off but not the way I'm using oil now. What do you guys think any of this make any sense?

 

Oil burning can be due to a valve seal or valve guide problem. However, I don't see that causing a loss of compression. I'd suggest pulling the injectors and having them flow tested.

 

are you saying a bad injector could cause the low compression in one cylinder?

 

Bad injector = lean mixture in one cylinder = detonation.

There's other possibilities. This is just a suggestion of one place to look. At assembly the piston fit or ring alignment could have been off for that cylinder.

 

detonation would only effect the compression if there was damage to the rings or broken ring land right? when doing the leak down it wasn't leaking into the crank case so wouldn't that mean the rings are still sealing?

 

I'm sceptical of your leak down results. New engines built for Nascar don't achieve 2% and rings always leak no matter how good the engine.

Anyway, there's only two places leakage can occur, valves or rings. Checking injector operation is something that can be done without engine disassembly.

 

You know now that you mentioned that I would agree I never heard of that low % of leak-down. I know it did have 9% on cylinder 1 on this last test, but wished we would of checked all of them. I asked him what would normal be and he said a good engine should be 2% to no leakage. That's why I like these forums because there's a lot of good knowledge to learn. Do you think it could be a bad valve seat that could cause the 145 psi in cylinder 1? Thanks for the replies.

 

Leakdown testing involves a very specific procedure and an equally specific testing device. It's anyone's guess as to which commercial testers actually conform to spec, but I can verify that at least some of the cheaper ones do not. As such, readings that most report should be taken with a grain of salt. This discussion I posted a few years ago is worth 5 minutes of reading:

https://www.evolutionm.net/forums/ev...wn-tester.html