compression test recommendations?

70SWT · 08:53 AM

EDIT to clarify: looking for tips on how to do a compression check on an engine on a stand i.e. out of the car, if possible, and without taking it to a shop, and recommendations for specific products available at a reasonable cost.

Thanks, Al

nimskov · 02-14-2009, 06:18 AM

I recently tested the compression on my car. I simply bought a compresstion tester at a local parts shop. It's no big deal.

The only slight problem with my tester is, that it can be bard to screw the hose in the plug hole, since the tube its flexible.

Other than that, remove all plugs, disconnect fuel pump, always test with full throttle, and run on the starter the same amount of revolutions for each cylinder tested.

Good luck

70SWT · 02-14-2009, 08:53 AM

Thanks for the tips! Original post edited as above.

nimskov · 02-14-2009, 11:05 AM

Normally the engine has to be at operating temp. when compression test is performed.

Not sure if it's a good idea to do it on an engine stand... there's no oil pressure and the temp is too low.

If you could rig a temporary oil tank, so the engine would get some oil, it could perhaps be done.

Hooking up a battery and making a temporary start switch should not be a problem.

70SWT · 02-15-2009, 03:54 AM

How about leakdown - doable on the stand, or similarly also only practical in the car?

911pcars · 02-16-2009, 12:53 PM

Posts above neglect to mention the starter motor needs a mount to rotate the engine. That means either a partial or full gearbox housing, and the required real estate for this gets a little tricky the way most engine stands are configured.

As suggested, the engine should be be close to normal operating temperature for accurate compression and cylinder leakage results, but while one shouldn't necessarily compare cold test results with factory specs, it's close enough for a very rough estimate.

Cylinder leakage testing requires the test cylinder to be positioned @ TDC end of compression. That task is the same with the engine installed or on an engine stand. Accessing the plugs and fishing loose spark plugs that fall out of the socket is easier on a stand, but that's quite minor. Preventing the crank from rotating is easier on a stand (lock flywheel in place), but for more accurate results, the engine should be at normal operating temperature.

Sherwood