Nicholas P.

iTrader: (1)

Last night I was playing around in the Garage and I got my compression tester out. I am wondering what the compression is supposed to be. The Engine is a 1984 with 1979 housings.

cdrad51

It's supposed to be over 100.

Hades12

Did you hold the valve open as you spun it over and look at each of the pulses?

90 is fine, 75 is low but should run Ok for a bit.

Nicholas P.

iTrader: (1)

Yes Hades12 my brother told me to do that. What kind of symptons does low compression give?

Hades12

Hard start and lower power.

dj55b

iTrader: (2)

Don't know if you have done so or not,

But you should try to grab some seafoam, pour some down the carb, turn the engine counterclock wise for about 5/6 turns by hand (you should be able to do this via the main engine pulley). If you have the time, let it sit for half a day in it, then turn it over 180 degrees for the other half of the day and then next day crank it up let it smoke up, and then do another compression test. You should be able to see some gain ... maybe not so much from the front, but more the rear rotor.

vxturboxv

iTrader: (2)

Not that I'm doubting the "magic sea foam solution" but why the hell would cleaning the carbon out of your housings and rotors give you a higher compression reading? If anything, shouldn't cleaning out the carbon lower the compression ratio? Your eliminating the carbon that is taking up space in your rotors? Just a thought I could be wrong...

If it were me I'd just swap over to some heavier oil. (If you haven't already). I'm at around 92 on the rear and 110 on the front with 40wt rotella. I was about 3 points lower on both readings with 10w30.

Also did you warm the car up completely and hold the throttle body on the carb open completely while you were cranking? (obviously remove the plug wires when doing this).

Good luck.

cletus

Carbon can cause seals to stick allowing air to leak by which would lower your compression.

vxturboxv

iTrader: (2)

Ah-hah! Told U I could be wrong... Although if you had a stuck seal I'm doubting you'd get comp numbers anywhere near 70's-90's. Unless it was partially stuck I guess... I find a daily flogging of 7k or so keeps my little 12A carbon free.

dj55b

iTrader: (2)

as cletus said ... its been proven before ... and i had about 7psi increase when i did it on one of my buddies engines ... every little bit helps

Nicholas P.

iTrader: (1)

I'm not trying to sound mean or anything but what does warming up the engine have to do with compression.... At the mechanic shop we had to use it all the time for piston engines.

trochoid

iTrader: (6)

If you read the testing proceedure in the FSM, it states that the test is performed on an engine at operating temps, 250 rpm cranking speed, etc. While a warm emgine may not show much of a psi increase, the measurements are taken using certain stard testing proceedures so one can determine the condition of the engine on a comparative basis.