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Night_Wolf
10-20-2011, 02:30 AM
So my best friend/roommate has a 97 Eclipse with a 4G63 7-bolt motor, and were working on doing an Evo 3 turbo swap on it as well as a few other minor upgrades and a re-seal. We decided to to a compression test on it and the results were as follows (+/- a few psi):
Cyl 1: ~160
Cyl 2: ~160
Cyl 3: ~145
Cyl 4: ~160

Think we should do a rebuild on it? I don't know much about compression tests and such so I thought I'd ask my favorite forum people

rizin
10-20-2011, 03:04 AM
My buddys evo had a problem like this. When he decided to rebuild it the piston was cracked in the center. I don't know if this could be anything like that. His was on cylinder 3 also.

temperacerguy
10-20-2011, 03:44 AM
I doubt it's a cracked piston.... you are within 10% of each other. so it's not HORRIBLE... could be ready for rings soon.

Night_Wolf
10-20-2011, 04:04 AM
My buddys evo had a problem like this. When he decided to rebuild it the piston was cracked in the center. I don't know if this could be anything like that. His was on cylinder 3 also.

We're gonna do a head gasket on it so I can check for that

rizin
10-21-2011, 05:22 AM
Ya one cylinder is ready for rings? I was just throwing it out there. I don't know the difference in the two engines I am just saying this because of experience first hand of one guys car. From what I here the evo viii can crack pistons. He thought it was rings after putting oil in the cylinder and the pressure raised on the compression test. I was just throwing it out there since I have seen it and I am no expert on any engine.

Luni
10-21-2011, 05:28 AM
Nah, 145 isnt a cracked piston. Id say youre ok. I wouldnt worry about it unless it was excessively using oil, smoking, or had less than 120 in that one, and the other 3 were high.

93celicaconv
10-21-2011, 01:45 PM
145 psi is pretty low. So are the 160 psi readings, but not terrible. That engine should be putting out 185 to 195 psi on a good block with tight, lapped valves. If you are only going to run the engine a year or 2 yet, probably will get away with it. But those pressure values are on the low side overall, and something unique is going on with cylinder #3.

T-spoon
10-21-2011, 04:57 PM
145 psi is pretty low. So are the 160 psi readings, but not terrible. That engine should be putting out 185 to 195 psi on a good block with tight, lapped valves. If you are only going to run the engine a year or 2 yet, probably will get away with it. But those pressure values are on the low side overall, and something unique is going on with cylinder #3.

Well, the overall lowish numbers could of course just be how they did the test.

93celicaconv
10-22-2011, 03:41 AM
Engine compression tells us at least 2 very important things - differential between cylinders, and magnitude of pressures. Both are equally important. I sense most people in this forum are more concerned with differential pressures than total pressures. That wouldn't be wise. Of course, a compression gauge out of calibration is problematic, but if all 4 cylinders were at 160 psi in this example, that's not great news. It means something is leaking more than normal involving all cylinders. Adding oil to the cylinders would help to determine what is causing the abnormal leakage.

temperacerguy
10-22-2011, 04:53 AM
Well, you're kind of vague about which engine you have... you say "7 bolt" which normally means you have one of the turbo engines (as you typically don't make a distinction between the differnt types of 420A engines).

The Turbo 4G63 engines typically have standard (NEW ENGINE) compression of 168-174, with nominal compression of 121 to 131. for the 97 4G63 7 bolt the standard compression is 178psi, nominal is 133

If you have a NA engine, the nominal compression is 145 and 146psi..

So, as I have said.... You're good all around.

Now, your compression is within 10% and you are well above the service limits for the engine (regardless of which 4G63 you have), so you are fine as far as service limits.

Typically with such a low variance in compression test results, you have a minor scratch down the cylinder wall, and you don't need to worry about it till it starts smoking bad, and it's time for a ring job (whenever you do rings, you always re-hone the cylinder walls (which will get rid of the scratch).
I am however of the belief that when you pull apart your engine, you're in for a penny, in for a pound... and you might as well do everything else that you can when you are in there... Valve job, re-seal and the like....

I'm not really sure where 93celi is getting his values... but that 97 7 bolt is a pretty low compression motor at 8.5:1 which is why compression tests show such low psi even when new from the factory. With the values of your test... the engine is fine with Good numbers.

93celicaconv
10-22-2011, 02:17 PM
My bad - I didn't see what engine was being referenced. I was thinking a 5th Gen NA Celica with the 4A, 5S or 3S engines. My error.

Luni
10-22-2011, 04:44 PM
RTFM N00b! :p

vip09
10-22-2011, 06:57 PM
Sounds fine to me. Was the test done on a warm engine or cold?

alltracman78
10-22-2011, 09:01 PM
turbo engines

Now, your compression is within 10% and you are well above the service limits for the engine (regardless of which 4G63 you have), so you are fine as far as service limits.

Typically with such a low variance in compression test results, you have a minor scratch down the cylinder wall, and you don't need to worry about it till it starts smoking bad, and it's time for a ring job (whenever you do rings, you always re-hone the cylinder walls (which will get rid of the scratch).
I am however of the belief that when you pull apart your engine, you're in for a penny, in for a pound... and you might as well do everything else that you can when you are in there... Valve job, re-seal and the like....

I'm not really sure where 93celi is getting his values... but that 97 7 bolt is a pretty low compression motor at 8.5:1 which is why compression tests show such low psi even when new from the factory. With the values of your test... the engine is fine with Good numbers.

This shit.

Turbo motors always have lower compression.....

Night_Wolf
10-22-2011, 09:34 PM
It was a cold engine

And actually on a side note, I'm trying to create a wastegate actuator bracket for my CT-26 (clocked turbo) does the actuator push or pull the wastegate open if that makes any sense....

vip09
10-22-2011, 11:07 PM
Did you hold the throttle open while testing?

DudeMan
10-23-2011, 03:26 AM
It was a cold engine

And actually on a side note, I'm trying to create a wastegate actuator bracket for my CT-26 (clocked turbo) does the actuator push or pull the wastegate open if that makes any sense....

It pushes.

The rod is under tension toward the actuator, which holds the wastegate closed, when positive pressure is fed to the actuator it pushes the rod outwards and opens the wastegate.

Night_Wolf
10-24-2011, 02:42 PM
Did you hold the throttle open while testing?
No we did not


It pushes.

The rod is under tension toward the actuator, which holds the wastegate closed, when positive pressure is fed to the actuator it pushes the rod outwards and opens the wastegate.

Thanks!

vip09
10-26-2011, 01:31 AM
Cold engine and closed throttle will give you low numbers.

93celicaconv
10-26-2011, 04:09 AM
Right. The repair manual asks that the engine be warmed up to normal operating temp, then shut off, ECU fuse pulled, spark plugs pulled, throttle plate wide open, and test all 4 cylinders relatively quickly. If not done this way, likely the values obtained will be lower, and not able to compare to a table of compression values proper for each engine.

Night_Wolf
10-26-2011, 02:09 PM
Cool thanks guys!

temperacerguy
10-26-2011, 09:56 PM
Cold engine, warm engine, oPen/closed throttle... It's all moot, your numbers are still good