Compression Test

[AUSSIEVETTEMAN]

Does anyone know what the factory PSI measurement is for an L81 engine.
I am about to do a compression test and am looking for the figure in the Chilton Manual and the original 1981 Shop Manual, but can't seem to find it.

I know she is getting a little old (22 years no rebulid yet), but I want to find out how much more she has left. Oil consumption is about 1 1/2 litres per 6 months, with about 6000 miles. She has two small leaks, one front seal and the other the rear seal. I think the valve stem seals maybe cactus, but we will see with the compression test.

Any Tips?


Tony

 

[mike weyman]

there is no definitive number for this.compression can change with mods to the motor.what your looking for is consistancy in numbers,they all should be within 10 % of each other.numbers like 150,155,148,152,etc are good, if the span gets too wide , like, 150,165,145,170,etc then you have problems.
if you have one that is particularly low,get it to top dead center on that plug, hook an air hose to the cylender, (adapter kit for compressor iS about5$) and let some air in, if it comes out the muffler, you have a bad exhaust valve,or if it comes thru the intake it is an intake valve.if it doesn't come from either, it's the rings.put an ounce of oil in the spark plug hole,if compression rises,it's because the oil stopped the air from coming out indicating bad rings.

 

[AUSSIEVETTEMAN]

...there is no definitive number for this.compression can change with mods to the motor.what your looking for is consistancy in numbers,they all should be within 10 % of each other.numbers like 150,155,148,152,etc are good, if the span gets too wide , like, 150,165,145,170,etc then you have problems...I see what you mean. We changed the head gaskets after one of the mechanics accidently dropped a nut from the Holley carb that a previous owner put on, down the back of the valve. While the heads were off, we noticed a bit of carbon on the pistons, but basically it was OK. The new gaskets would obviously change the compression numbers. BTW, the Holley got the chop and there now lives an Edelbrock QJet on top of that Edelbrock manifold.
...if you have one that is particularly low,get it to top dead center on that plug, hook an air hose to the cylender, (adapter kit for compressor iS about5$) and let some air in, if it comes out the muffler, you have a bad exhaust valve,or if it comes thru the intake it is an intake valve.if it doesn't come from either, it's the rings.put an ounce of oil in the spark plug hole,if compression rises,it's because the oil stopped the air from coming out indicating bad rings...I'll let you know!

She does not blow any white smoke, but you can smell oil fumes in with the normal exhaust. It is just fumes at this stage. you can smell this when you are following her during driving and while she is idling over in the garage.
Thanks

Tony

 

[mike weyman]

could be valve seals,will give the smell and costs little to fix.