Compression Differences between heads

satancom · Post by **satancom** » Sun Jan 24, 2010 5:06 pm

Evening all,

Some of you may remember I posted just before new years that my engine suffered a seriouse ovr heat and compression was down to 80psi or so per cylinder. Anyhow I put new heads on over new year break and have only now had a chance to do another compression test.

Anyhow the right hand bank (drivers) is around 120psi, the left bank is 140-150 psi. The engine was rebuilt with rings and bearings around 3500 miles ago but before the overheat.

The heads I put on came from an engine that had been rebuilt by someone else and sat in his garage for a few years, so it is indeed possibly they were not a matched pair as history is unkown.

I was wondering if its possible the valves on the right bank are not closing properly, maybe due to the rocker pedestals needing shimming or something?

ANyhow engine runs fine and pulls like a train. The comression test was down with a warm engine and no oil in the bores.

DEVONMAN · Post by **DEVONMAN** » Sun Jan 24, 2010 6:13 pm

It would be first of all worth checking the head numbers against the STICKY at the top of this section.
Regards Denis

ChrisJC · Post by **ChrisJC** » Sun Jan 24, 2010 7:18 pm

There are two different combustion chamber cc's, even with nominal 36cc heads. On some heads the valves are more recessed into the seats. I don't know why, from what engines, or how you can tell short of a visual on the combustion chambers.

Chris.

SuperV8 · Post by **SuperV8** » Sun Jan 24, 2010 7:30 pm

Can you do a leak down test? Takes out the variable of battery condition and number/ time of cranking for each cylinder.

Tom.

satancom · Post by **satancom** » Sun Jan 24, 2010 7:57 pm

I assume you need a special piece of kit to do a leak down test?

The bank thats shaowing 120psi was the first to be tested so battery condition should not be an issue (its a good battery too). Also the engine was cranked 5 times for each cylinder. I went back to cylinder 2 (120psi) after I completed the tests to check and came up the same.

The heads were inspected for true before fitting and cleaned side by side so I imagine they are both the same type as both me and my mechanic pall had a good look at them together but one may have been skimmed. I will check the types in the morning!