Compression test questions

[Michael Oritt]

I did a compression test on the MGA engine in my Elva and got the following results (reading from cylinders 1-4):

Engine cold : 156-148-137-158

Engine hot: 137-140-125-145

W/squirt of oil: 147-150-133-160

It seems that cylinder #3 is low by about 10-15% across the board. But does the fact that the oil squirt raised all readings up proportionally point toward a bad exhaust valve in that cylinder? Would a leakdown test be any more significant?

 

[DrEntropy]

MUCH more telling, Mike. A "listenin' pipe" in the form of a piece of 1/4" fuel line and you can tell if anything is leaking into crankcase (by listening down the oil fill hole), the exhaust or the intake (a bit more obvious just where to stick th' "pipe"). And with the gauge it can indicate just how bad the leak may be.

 

[jlaird]

Just from those numbers I would say valve first.

 

[Hap Waldrop]

How about a leak down test, it would isolate the problem.

 

[jlaird]

Yep, that is the final answer.