Possible to compresssion test engine removed from car?

[Riick]

I want to verify that the head gasket / rings / valve seals are good on an engine I want to buy. Is there some way to test compression on an engine that's been removed from a car? (like by using an air compressor or else by jumping the starter or something?)

 

[RealRabbit]

Sure, as long as you can turn the engine over. I.e. jumping the starter.

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[mymmeryloss]

Yep. Jump the starter...


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[Riick]

So if I jump it...
1) Does the engine have to be braced so that it doesn't move around?
2) Coolant will spit out of the output nozzles? right?
3) Does the engine need to have oil?

 

[itsmycookie]

you should have the engine somewhere stable. like an engine stand or sitting on a pallet and being braced so it doesn't tip over.

you aren't starting it so you dont really need to have coolant you're just using the starter to turn it over.

oil is always needed. you would damage the engine without any oil and your test wouldn't give accurate results

 

[Riick]

oil is always needed. you would damage the engine without any oil and your test wouldn't give accurate results

Good info.
Turns out he's already removed the tranny! I guess we'd have to install the tranny, add engine oil, add tranny oil, brace engine, test the engine, drain engine oil, drain tranny oil, remove the tranny. Ick. And draining the fluids might be tough since we have neither stand nor hoist.
The engine has less than 120k and seller claims it ran great before he decided to upgrade. It's a great price too. How stupid would it be to buy without testing?

 

[TokyoSkies]

Good info.
Turns out he's already removed the tranny! I guess we'd have to install the tranny, add engine oil, add tranny oil, brace engine, test the engine, drain engine oil, drain tranny oil, remove the tranny. Ick. And draining the fluids might be tough since we have neither stand nor hoist.
The engine has less than 120k and seller claims it ran great before he decided to upgrade. It's a great price too. How stupid would it be to buy without testing?

Really depends on your plan/budget. I usually buy a motor with the thought that it's going to have shat internals anyway, and plan to rebuild it. That being said, if you want a direct drop-in, yeah. It's a bit risky. If you don't have the funds to replace piston rings, do a valve job etc., I'd ask a LOT of questions and ask for any and all recent receipts for oil changes etc.

 

[Riick]

Really depends on your plan/budget. I usually buy a motor with the thought that it's going to have shat internals anyway, and plan to rebuild it. That being said, if you want a direct drop-in, yeah. It's a bit risky. If you don't have the funds to replace piston rings, do a valve job etc., I'd ask a LOT of questions and ask for any and all recent receipts for oil changes etc.

Thanks.
As for that engine, I checked carfax and the mileage on that guy's car is more like 260k. Some other differences too; I think the guy got cheated. Anyway, not a low mileage engine after all, so even more risky than I thought.

 

[Riick]

Going to test it after all... do we need to put lube in the manual transmission before testing? (The seller figures the only part of the transmission that will move during the test is the flywheel so we can leave the transmission dry; is he correct?)

 

[itsmycookie]

you're just compression testing the engine. you dont need the transmission hooked up since it would be free floating in neutral

 

[Riick]

you're just compression testing the engine. you dont need the transmission hooked up since it would be free floating in neutral

The issue is that the starter motor is attached to the transmission housing. So we're both assuming that the only way to use the starter motor is to bolt the transmission back on. I just want to verify it's OK to crank the engine with the transmission dry. Assuming yes since it will be in neutral, but just want to verify.

 

[KillaGuizEj8Si]

Where in mass are you. Also there are YouTube videos to this even if you don't have a tranny on you could still do it my turning the crankshaft but you have to be strong. Beware of deals to good to be true. Only engine oil is needed your not gonna start the motor just turn it over. The tranny woot even move and look for consistency not just high numbers. My ls was 200-205psi over all four , my gsr 225psi and my b16 215 over all of them. If it's off by 8-10% be careful

 

[Riick]

Where in mass are you.

Boston area.

Also there are YouTube videos to this even if you don't have a tranny on you could still do it my turning the crankshaft but you have to be strong.

Good to know! I'll look into this. How likely is it that the readings will be inaccurate due to the engine being cold? (I know it's best to do a compression test when the engine is at operating temperature to avoid inaccurate readings.)

The tranny woot even move and look for consistency not just high numbers. My ls was 200-205psi over all four , my gsr 225psi and my b16 215 over all of them. If it's off by 8-10% be careful

Thanks. Honda's service manual says nominal is 185psi, minimum is 135psi, and maximum variation should be less than 28psi.

 

[Riick]

Is it typical to get low numbers on cold removed engine? The numbers I mentioned above are supposed to be for an engine at operating temperature. I'm trying to find out whether numbers below what I menationed above necessarily means the engine needs attention.