Dropped Engine, can I still do a Compression Test?

[wilson234]

I dropped my engine to repair a clutch issue. Then found a broken head stud, not working on replacing studs.

I didn't expect to have to take apart the engine, and didn't have any running condition issues with the engine prior to drop. But now I'm thinking if I'm going to tear into the engine, I might as well spend the $$ for any machine work that needs to be done. Engine has 88K miles from 1989 964.

My question is can I still run a compression test? I read this typically is done with a warm engine, which is not possible now since it is removed from car.

Maybe it will not be as accurate but I'm assuming a cold engine might show lower compression across all cylinders, but I guess if they were all consistent it would be a good sign.

Can a compression test be peformed by cranking the engine by hand? Given the starter is removed from the engine.

Any help would be appreciated.

Thanks!!!

[Spumato]

Yes, you can do a compression test by hand with an air compressor to fill the cylinders from the spark plugs.

[Spumato]

Keep in mind that cylinder leak down of 5% is the norm. Anything up to about 12% should be acceptable.

[boosted79]

No, you can't do a comp test by turning the engine over by hand unless you are superman and can turn it at cranking speed.

['76 911S 3.0]

Leakdown test is the only thing you can do at this point

[kclem19]

Pull the transmission, bolt it to the engine, install the starter, and bump it over with the starter with jumper cables....

[Spumato]

My bad... I did get my terminology crossed. I was working the leak down arena. My apologies. Compression test does have to be done with a running engine, sorry!

[iamtheari]

How much error do people see from a warm engine leak down to a cold engine leak down? I want to do a leak down test on my engine, which is running and in the car but almost ready to drain the oil and drop for a clutch replacement. But it seems really tedious to get to the spark plugs when the engine is still warm given the amount of stuff that has to come off to get to them. I assume people come at it from the lower spark plugs on the dual-plug engines when they're in the car, since #3 and #6 are impossible to get at the top side of with a wrench, much less a leak down tester. Doing it on a cold engine sitting next to the car seems like a lot easier job than a hot engine still in the car.

[Josh D]

You can still learn a lot from doing a leakdown on a cold engine, even if leak percentages are a bit higher on a cold engine. What you are looking for is variation of leak percentage among the six cylinders and where the leak is going. Still very useful if you are trouble shooting or checking general condition.

[911pcars]

Originally Posted by kclem19

Pull the transmission, bolt it to the engine, install the starter, and bump it over with the starter with jumper cables....

Yes. You have the cylinder with the broken head stud as a reference. Even though the engine is cold, compression results from each cylinder can be compared with each other as well as the affected cylinder with the two-piece head stud. You'll want an idea of the condition of the piston rings. How far you go depends on your inspection at each step.

Sherwood