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[colt45]

i need to get a new motor, and i have sourced one, but i want to do a compression test on it before handing over money.  can i do a compression test with just a breaker bar and a socket on the crankshaft?  the motor is out of the car and on the garage floor.

[t_cel_t]

i tried using a breaker bar once but it leaks past the rings too fast to see anything over 50psi, just hold it up and jump the starter

[snm95ls]

leak down test works well
only problem is when the engine is cold the leakage will be more.
you can get the leakdown testers at harbor freight, but the directions are wrong.
fucking chinese labor.

Didn't know that.  I may have to pick up another tool.

 ;D

[Adam Lofton]

Nah, you are never going to be able to crank the engine fast enough to get a good reading. Also make sure the throttle body is WIDE open.

[HiProfile]

I prefer to do it at 80psi max and just deal with the math. High-end mech gauges are usually 2-3x as inaccurate in the first and last 15% of it's display range. Just my particularities, as JD might say.

A cold motor won't show the best numbers, but usually enough to see what's up. If you look at how the starter wires are in a car, its just 2 direct connections interupted by a high-amp relay (starter solenoid). Just brace the motor against a wall and jump the starter with a battery and jumper cables - carefully. And make sure you keep the TB open...

[colt45]

yeah, the motor to be tested will be cold and on the floor.  i just want to get be sure its not completely fucked.  thanks for the link to the leak down tester.   so , you put oil in the cylinder, put the tester on and hook up the air compressor and watch the guages?

[colt45]

it was my understanding a leakdown test used oil?

[Joseph Davis]

If dude has trans + starter, it's on.

[Adam Lofton]

yeah, the motor to be tested will be cold and on the floor.  i just want to get be sure its not completely fucked.  thanks for the link to the leak down tester.   so , you put oil in the cylinder, put the tester on and hook up the air compressor and watch the guages?

1) No oil in the cylinders, that will give you a false reading that the cylinder leakage is less than is actually is.

2) You have to preform the test with the cylinder at TDC on the compression stroke.

[Robb]

yeah, the motor to be tested will be cold and on the floor.  i just want to get be sure its not completely fucked.  thanks for the link to the leak down tester.   so , you put oil in the cylinder, put the tester on and hook up the air compressor and watch the guages?

1) No oil in the cylinders, that will give you a false reading that the cylinder leakage is less than is actually is.

2) You have to preform the test with the cylinder at TDC on the compression stroke.

Also, be careful you dont leave the wrench or ratchet whatever you used to turn the crank, on the crank bolt. Danger. If the piston isnt dead nuts on TDC, the air will force the piston down and toss the ratchet at you. 

[magik123]

oil in the cylinder is a wet compression test not leakdown test.  If you get much higher compression with oil compared to without oil u can guess the rings are shot.