rx_rotary

I tested the compression on my 1979 12A rx7
with the engine cold and a regular piston compression
tester with the shredder vavle in.The compression
was 105 on both rotors.Is that good,average or bad?

hanman

If you use a conventional tester, with the Schrader valve still intact, you must hold the pin in. This will allow the pressure to release and not hold the reading, otherwise you are only going to get one compression reading instead of the three that you need. Here is the procedure:
Disconnect the fuel, however you want, disable the pump, constrict the fuel line, whatever.
Disconnect the spark plug wires.
Hook the compression gauge up to the top (trailing) spark plug hole. I would take the other trailing plug out also.
Have someone sit in the car and hold the gas pedal to the floor while turning the engine over.
Hold the pin in on the compression gauge (this is the Schrader valve).
Check the readings while the engine is turning over. You will see the needle bump up and down. You are looking for three readings. i.e. bump, bump, bump. They should be consistent with each other. Like if you get 105, 100, 103. If they are not, you have problems. It helps if you turn the engine over for a number of rotations.
Then do the other rotor.
If you do not have consistent readings, come back and post your numbers, we will let you know what's happening with them.
hanman

85TIIDEVIL

iTrader: (2)

I know this is a old thread... but I just did a compression test w/a piston compression tester just like described above and I'm getting 90 all around on both rotors...

Is that low...? It's a 74 13B 4port. I did the same test last summer, with the same tester and got 110 all around.

I re-tested her compression b/c I'm having a REAL rough time starting her when it's cold out (well not even that cold out, 35* or less) and all the ignition stuff was just replaced... battery, cap, rotor, wires, plugs, alternator.

IanS

iTrader: (4)

Do you drive the car around a lot? If you have put a bunch of miles on since last comp check then maybe this would explain the huge drop in comp. 20 psi drop in a single year seems like a lot unless it was overheated or something. If the engine has not run very much maybe it needs a little seafoam action to clean it up decent and recheck. Only thing its gonna hurt is the 10 bucks it costs for the bottle or whatever, which is worth a try in my opinion.

I also wouldnt think that even with 90 all around that it would have that hard of a time starting when cold like you describe. Could very well be the reason though.