Checking compresion on engine not in a car?

[4twenty]

Is it possible to get an accurate compresion reading while an engine is out of the car? Does the valve cover need to be bolted on to do the test? I have an engine that I am trying to sell but would like to check the compresion before I sell it.
Thanks
Jared

 

[Defiant]

Better to do a leak-down.

http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm

No, the valve cover is only there to keep oil from spraying all over the place.

 

[BOOSTED11SECTSI]

To get a true reading the motor has to be running till it is warm. Then shut it off and do the test. So if you can run the motor for a lil bit then check it if not it wont be as true.

 

[char]

metal expands when hot ... all igot to say y cars idle low in cold starts then run faster as they get warm

 

[Eight Ball WS6]

metal expands when hot ... all igot to say y cars idle low in cold starts then run faster as they get warm

every EFI car Ive driven has idled faster when cold and slower when warm ESPECIALLY in below freezing conditions...

 

[Gigaah]

every EFI car Ive driven has idled faster when cold and slower when warm ESPECIALLY in below freezing conditions...

yep, they high idle for a long ass time in the winter some of them.

 

[set3422]

Is it possible to get an accurate compresion reading while an engine is out of the car? Does the valve cover need to be bolted on to do the test? I have an engine that I am trying to sell but would like to check the compresion before I sell it.
Thanks
Jared

Actually I was thinking about doing something similiar to this. While I have my engine out, I was going to extend the engine electrical harness from the bay to about 5 feet long. This way we can start the car and check for odds and ends before we drop it in the bay. The tough part is to get some AN fittings and lines for extending the fuel feed and return line. I don't know if the engine stand will be able to withstand the vibration from motor though.

 

[autronicDSM]

Probably not. You will need a solid stand bolted to the floor a la engine dyno.

As far as checking compression goes, you could just hook up a starter to it. Reading will be little lower but at least it will show if the motor is dud or not. You'd have to fabricate a bracket though to bolt it somehow to the engine.

 

[1fast97gsx]

or just use a 1/2" ratchet in the stand and keep rotating it .. I suppose an impact gun would speed up the process. Get 4 compression guages and you can do them all at once even

 

[autronicDSM]

Air tools *might* work. Forget turning it by hand. You need to spin few hundred rpm for it to build any compression. Ask me how I know.

 

[set3422]

Probably not. You will need a solid stand bolted to the floor a la engine dyno.

As far as checking compression goes, you could just hook up a starter to it. Reading will be little lower but at least it will show if the motor is dud or not. You'd have to fabricate a bracket though to bolt it somehow to the engine.

Yeah when we built our 600cc formula kart at PSU, the engine stand was vibrtaing like a mug when we started the motor.