35 replies to this topic

[Gremlin]

Old torque wrench wasn't torquing as high as the new one is (under torquing)

Under torquing will not produce these symptoms

[minivanman8]

I know. Hence why I'm stumped! I can't remember what temp the engine was when I did compression test last time. It was virtually running temp this time.

Still haven't a clue why bubbles were forming around the head nut though. Like I said, it's gone after re-torquing. Will have to find out how it drives when I have the brakes working better

Edited by minivanman8, 10 May 2014 - 08:57 PM.

[Ethel]

Compression tests are only vague indicators. The biggest variable is how much air you trap before the valves close, which depends on induction restrictions and cranking speed, neither of which have much to do with the engine itself. Try and replicate the test conditions across tests to make them more meaningful, fully charged battery (with the same CCA), all plugs out, air filter off and throttle wide open.

[minivanman8]

Good shout....engine had to be jump started and compression test was done after about 15 minutes of running....so it wouldn't have been a fully charged battery.

I'll stick it on charge and try the test when the engine is cold

[Captain Mainwaring]

Compression tests are only vague indicators. The biggest variable is how much air you trap before the valves close, which depends on induction restrictions and cranking speed, neither of which have much to do with the engine itself. Try and replicate the test conditions across tests to make them more meaningful, fully charged battery (with the same CCA), all plugs out, air filter off and throttle wide open.

 

On a VV carb throttle wide open isn't enough, you need to physically lift the piston too.

[Ethel]

While it's true the piston is a restriction, if it was a significant one the inlet depression would lift it for you, either way it will be as constant as the cranking speed to give results you can compare.