Compression testing motor on stand?

[beatle]

Heyo,
I have an engine I am about to throw into my car, but before I do, I'd like to know if the engine is any good. How can I test the compression while its on a stand? I tried cranking it by hand with a compression tester in but it didnt budge the needle. for referance, it has no manifolds on.

Cheers
Mike

[dangdang]

Rig the starter motor up (may require the box also to bolt the starter) and crank her up on a battery

Also hold the throttle wide open WOT and test wet and dry all cylinders to be sure she's a goodin.

edit..no manifold no WOT needed, point of that being to fill the cylinders fully whilst cranking.

If you find a cylinder down on pressure a few drops of oil down the plug for a wet test, and if the pressure increases its bad rings, no diff, bad valve.

[DrNick]

i can see that going pear shaped very easily

[dangdang]

Basically all that needs to be done is to turn the engine over at starter motor speed, can't do that....can't compression test....

Also obviously my assumption is that the engine has no fuel or ignition connected....as a runner on a stand might not be best...

[beatle]

hmm, to put starter on I will need to pt on gearbox, to do that means I have to take the engine off the stand, to do that I have to borrow the engine crane, too much and then. Might try pneumatic ratchet to get it humming.

[MR22ZZ]

leakdown test?

[dangdang]

hmm, to put starter on I will need to pt on gearbox, to do that means I have to take the engine off the stand, to do that I have to borrow the engine crane, too much and then. Might try pneumatic ratchet to get it humming.

Will want to be a big ratchet, I doubt even a grunty 1/2 inch air ratchet won't stall on the front of an engine, though there is options...

Just need to get it spinning at a nice consistent rate.

[boona]

As far as needing a gearbox, I used the thin metal sandwich plate that goes between the bellhousing and block.
I was concerned that it would flex and allow the starter motor to jump teeth on the flywheel, but it was fine.

[beatle]

leakdown test?

I was hoping there was another way, as I dont have a leakdown tester, but they are always a useful thing to have I guess, so good excuse to buy one

[allencr]

...cranking it by hand with a compression tester in but it didnt budge the needle.

Turning the wrong way or slowly would still show some compression, so has it been sitting a long time with the cyls rusting up?

If it isn't that or maybe that the cams aren't turning, it's dead!
I would try some oil for laughs and not bother with leakdown, excuse for a new tool or not. It oughta be at least 30-50 unless you're turning it at less then 1 RPM!

[CrUZida]

If the engine has been sitting around for more than a few months then you are wasting your time doing a compression test.

You need to get some heat into the motor to free up all the valves and get them to seal properly.

If you just want to know that all cylinders have compression, then remove all the plugs, turn the motor over by hand, and block each cyl one at the time with your thumb (or similar), you should feel some compression being produced.