can you test rotary compression with the engine out of the car?
 

as the topic says. the engine i have tried this on i am using a breaker bar to turn the eccentric shaft pully, i am getting almost no compression out of either cylinder. i have no idea if the engine runs or not but it has been sitting for a few years untouched. any ideas on how to tell if its good before i put it in the car?

When I turned my engine over with a ratchet and socket (out of the car), I got a whooshing sound out of the the spark plug holes. The Bruce Turrentine video shows this as a way to check compression if the engine is removed. Other than that, I don't think there is an easy way. You can also look through the exhaust ports and inspect the apex seals.

I would try turning the motor with an impact wrench on the front pulley and use a modified compression gauge to take a reading. This will not be as accurate as testing the compression in the car because an impact wrench will not turn the motor as fast as the starter.

A ported race motor I have has the compression numbers written on the bottom of the rotor housings (visible with the oil pan off). They read something like (9.4, 9.3, 9.5 @ 200 rpm) for each rotor. I imagine the engine builder used an impact wrench or something simular to get the motor to turn at 200 rpm for a reading.

Keep in mind that if the motor has been sitting for a long time the seals are probably carbon glued and it will not show any compression but might be a good motor if you loosen the seals up with a treatment of ATF.

Try this:
Put some ATF in the plug holes (or directly in the intake ports if the manifold is off) and rotate the motor a few times by hand. Do this a few times to be sure you have some ATF in each chamber. Let it sit overnight and put more ATF in it. Then try getting your compression reading while turning the motor with an impact wrench.

I can't tell you what I think would be acceptable compression numbers so use your own judgement.

Ugh... Are you serious? This is *terrible* idea! There is no way an impact wrench will even turn the engine over, and it may even over-tighten and/or break the front pulley bolt. And then you'd really be screwed.

Have you used an impact gun before? It works by giving the nut/bolt very sharp 'impacts'. If there is any resistance at all to the crankshaft, it will not turn. And since you will be turning against compression, there is no way this would work.

The ATF is a good idea, though.

Yea.. And I have used an impact wrench to turn a motor over.

thanks for all the replies guys. i actually did try to turn it over with a drill, but it didnt have enough torque. my sissy electric impact wrench couldnt turn the motor over when i was installing my crank pully, (allthough it did get off the 2 1/8" flywheel bolt with no problem =).

turning it over by hand yeilds about 30 psi (as fast as i can turn it). i did inspect the apex seals and they look good, and i bought some MMO today to try to loosen up the side seals (which ironicly is the reason the last motor died). hopefully that will do the trick. if all goes as planned ill install the motor tomorrow and see if she cranks.

the best part is the motor is going in my it-7 race car, if it wins anything ill prolly cry =)...

I would love to see that. I've used impact guns to remove pulley bolts, and it does not have enough constant torque to turn the motor over.

Remove the exhaust manifold and look in there . rotate untill the apex seal is centered in the port. push on them all to see if they are moving . Or bolt the motor to a transmission and starter , crank away. My mechanics friend has a test stand and they run motors out of the car s for testing.

Don't use an impact gun, use an air socket. Works great as it provides constant torque vs. the impact where you might hurt something. Also, a shop here in town has an electric bellhousing that bolts up to the motor and plugs into a 12V source to turn the motor at starter speed. That would be the ideal choice, but pricey.