Quote:
Originally Posted by ProwlerGT
Is it possible to have a bad valve or piston and compression still tests good or ok?
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The only scenarios I can think of where something related to a valve would show good compression and leak down would be:
1) Collapsed lifter - valve would stay closed all the time. If this was the case, it should make a horrible racket, especially at idle and it may get better with rpm as oil pressure increases??
2) If there was a broken valve spring (broken on either end). The broken spring would have enough force to open/close the valve while cranking during a compression test, but it might not allow the valve to close fully every time while. If this was the case, you'd assume it would get worse with rpm because the valve would be floating??
3) If the valve guide was worn, which would allow the valve to oscillate and occasionally it would not seat properly. If this was the case, one would assume the valve guide seals would be bad as well??
This list is not comprehensive, its just the only scenarios I can dream up at the moment. Please feel free to correct or add on to my list.
Otherwise, a bad valve should show up as poor compression and/or leak down.