Tuesday, March 16, 2010

Compression test results

Well, I picked up a cheapie compression tester from Ebay ($30 Aud delivered) amazingly cheap. Seems to work OK.

Results were 150 psi on all cylinders.

Importantly they were all the same, so, perhaps the leaky gasket is not telling me I need an engine rebuild.

As they say here:

As a rule, most engines should have 140 to 160 lbs. of cranking compression with no more than 10% difference between any of the cylinders.

Low compression in one cylinder usually indicates a bad exhaust valve. Low compression in two adjacent cylinders typically means you have a bad head gasket. Low compression in all cylinders would tell you the rings and cylinders are worn and the engine needs to be overhauled.

I will now locate the parts and tools to replace the head gasket.


  1. Hi JB Vanman -

    Great compression results! Being even at 150 psi indicates that all is good in the head and combustion area, which is good news ... you've just saved yourself about $900!

    Before you go taking the head off, if the oil leak is coming from between the block and the head there's a good chance that it is leaking from around the rocker gear or a pushrod to the outside. It would be worthwhile running the engine up to normal temperature, then torquing the head down. There's a chance that this may be enough to stop the leak.

    Well worth a try!

    Cheers - Bugly

  2. Thanks, I will certainly try that. Taking the head off is pretty involved, by the time the carby, exhaust and radiator connections come off.

    Great idea.

  3. Hi again -

    The head removal is not too hard a job, but it would be good if you didn't have to do it! Don't forget to re-adjust the tappets after re-torquing the head, as you'll open the gap a tad. The good book shows both exhaust and inlet valve clearance (cold) at 0.015 inch (0.38 mm)