So I bought a car with a brand new rebuilt motor and In November I went out and bought a compression tester from Harbor Freight. Tested the motor and both rotors were at about 110psi. Fast forward to today and I measured just the rear rotor to see how things were coming along. It said 60psi, I was stunned. It starts up, runs and drives the same, pulls the same amount of vacuum.

Does anyone have experience with having a tester go bad? I also let a friend borrow it and he got 60psi also on his motor.

 

Either the tester is no good or you're not using it properly.

You can generally tell the health of an engine by how well it starts and idles and how much vacuum it pulls. A motor that cranks and starts nicely, starts easily when cold, has a smooth idle, and pulls good vacuum is fine.

Did you have the throttle wide open when you did the test? Was the tester fully screwed into the plug hole? Was the O-ring at the part of the tester that screws in to the motor present, in good shape, and sealing?

For me, the number the tester shows doesn't mean much. Holding the relief valve in and watching the pulses and their pattern means far more. And, I can tell if a motor is flaky or iffy just by listening to it idle and start.

Dale

 

http://www.rotaryresurrection.com/3r...ion_check.html

I used the method in the above link. I didn't check the pulses. I will redo that and let you know. Is 60psi even startable?

 

This is just the sound with both lower plugs removed. I also wanted to check that the throttle was opening all the way.

 

Pulses for rear rotor

 

Everything sounds fine and dandy to me. I don't think you have anything to be concerned with.

If you've lost compression, you'll know it. Typically you bring in the compression tester to check the engine in the troubleshooting process or to check the health of an engine that's an unknown quantity, like when buying a car.

Here's a blown engine, I just dug this up on Youtube. Guy barely seems to know what he's doing, but the important parts are listen to the engine start and listen to the exhaust on the outside when it's idling. The pertinent part starts at around the 3 minute mark -


Dale

 

Thanks Dale. Im a little less worried now.


Here is a hot startup and idle video

 

Sounds fine to me. Go drive and enjoy!

Dale

 

Do the tests again in a week and see what happens.
Make sure it is done correctly. Have somebody help you.
If the same happens again, then you it is bad.

I once tested an engine that the rear was good and the front had all three faces with 0 psi.
It started totally normal but idled a little rough.