i did a compression test on a 12a today. i let the car warm up, unplugged the fuel pump from the connection underneath the drivers side bin and also took out the fuel pump fuse. after doing this i took out the top plugs and i used a snap on compression tester. i just screwed it into the plug hole and had someone turn it over until the needle stopped. on the front rotor it went and stopped right at 100. now heres the weird part, on the rear rotor it shot to between 175-200. i had the person turning the key stop when i saw what it was doing. i tried it twice and both times i got the same results. when i went to push the valve to release the pressure it seemed as though the vlave was harder to push, but maybe its me. what the heck is going on?? is this bad or did i just mess up?

 

i thought you can't use a standard piston compression tester on a rotary? maybe that's why it's not working...

Alvin

 

You can use a piston compression tester just fine. The readings will just be lower than expected. Anything between 90psi and 110psi overall on a piston engine compression tester is good. Actually, a rotary will run on a compression of 50psi, just won't have much power. My 6 port 13B turned out 105psi overall on the front rotor, and 107psi on the rear and the engine has about 40000 miles on it.

As for your 200 psi reading, I suggest you check the compression again. Just this time check it before you run the engine. Its possible that there was somehow some excess oil in the rotor housing bumping up the compression numbers quite a bit.

 

Did you take the shcraeder valve out of the tester before use?

 

You don't HAVE to take the schrader valve out. Taking the valve out simply makes it so you can check the compression on each face of the rotor. Leaving the valve in make it so you can check the highest compression reached over the 3 faces of the rotor.

 

Which is exactly what you want, Individual numbers.

 

The valve doesn't account for the 175-200psi reading, does it?

 

Which tells you jack sh*t...... getting 140 PSI as highest is nice for example, but if the 2 other apexes give 70 PSI......

you need individual numbers...end of story.