When doing a leakdown test the cylinder should be at TDC. With the cylinder in this positin will the compression release affect the leakdown test? I know that as the engine starts the release is deactivated. But when the engine is not running shouldn't the release have the exaust valve open? Is the same thing true if doing a compression test by just pulling the rope and not spinning it fast enought to release the compression release. Maybe I am not understanding how the compression release works. Any help or information or explanation will be greatly appreciated. Thanks for all your help.

Russ

most comp release mechanisms i am familiar with only open the exhaust valve for a fraction of a second.if its an ohv engine you can see the valve bumpopen for a second after the piston goes past tdc. most instructions i have read for doing a leakdown test entail securing the crank in a certain position to insure a reliable test. r u doing that? :wave:

When doing a leakdown test the piston needs to be at TDC. You may have to lock fly wheel to keep air from pushing piston down.