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Fri Dec 13, 2024 3:46 pm

I will soon be going to the scrapyard to pull an EJ25. Does anyone know what “good” compression numbers would be when turning the crank with a wrench? The junkyard compression test gives lower numbers but I want to know what to look for. Maybe somebody with a good EJ25 would be kind enough to do a hand compression test for me?

Fri Dec 13, 2024 4:18 pm

I'd love to know that too!! BUT, cold engines are very poor candidates for compression testing. I'd be feeling mor for consistency in each, rather than a number.

My EJ22 ran great, but when cold, one cylinder showed 90'ish with the others in the 140's.

Fri Dec 13, 2024 7:26 pm

CowardVenus15 wrote: I will soon be going to the scrapyard to pull an EJ25. Does anyone know what “good” compression numbers would be when turning the crank with a wrench?

you're kidding, right?

there is zero way to accurately even do this, let alone have any numbers that are meaningful. I can fart harder than you'd ever turn an engine by hand and get any compression

I mean, you're in a junk yard. bring a battery and jump the starter. if you can't do that, you may want to rethink things....

Fri Dec 13, 2024 8:23 pm

As others have pointed out, compression tests need to be done while the engine is warm and you cannot do it by hand.

That being said, I have purchased several (10+) engines from various dismantlers and JDM engine suppliers (GM LS/LT, Toyota 2JZ, Nissan RB) where the compression tests were performed at ambient temperature (engine removed). Use a battery and turn it over with the starter motor.

These are the factory values for a warm 2001 Subaru EJ251:
Compression (350 rpm and fully open throttle)
Standard; 1,275 kPa (13.0 kg/cm2, 185 psi)
Limit; 1,020 kPa (10.4 kg/cm2, 148 psi)
Difference between cylinders; 49 kPa (0.5 kg/cm2, 7 psi), or less

As long as you have good compression (within 5-15% of the warm value) AND more importantly the values are within 7 psi you should be fine. Remember to hold the throttle wide open when performing the test. With used engines, usually the lower the miles the better. Make sure you do the head gaskets and whatever else is necessary for the particular engine. I've had great results with pull out engines. YMMV.

I've purchased a several good quality used engines from JDM Engine Bay in San Leandro, CA.
https://jdmenginebay.com/

Fri Dec 13, 2024 9:39 pm

Assuming the engine hasn't been tilted to the point oil in the sump has come into contact with any one or more of the pistons, you can do a pseudo compression test by turning the engine by hand. The numbers will in no way be meaningful so don't even bother with a gauge, but with the spark plugs installed you will be able to tell whether each cylinder has compression or not by the feel. You need to turn the engine over in the direction of normal operation, typically clockwise when looking at the engine from the pulley end, and rotate the engine at the same speed for each cylinder trying to maintain a continuous motion from BDC to TDC as best you can. If all the cylinders feel the same you are likely golden, and if not you likely are not, but there are zero guarantees either way. Using a long handled ratchet can help in giving consistent results.

Sat Dec 14, 2024 1:41 pm

I got about 30psi per cylinder with the wrench on the crank from the engine I pulled. Gonna call that good compression and it was consistent. Fingers crossed there isn’t anything I’m overlooking on this one.

skills@eurocarsplus wrote: I can fart harder than you'd ever turn an engine by hand and get any compression This guy farts hard.

Sat Dec 14, 2024 5:01 pm

Stay up-wind of Skills! Check! :shock: :shock:

Hans