Leakdown Test With Motor Out.

[Bl4cK32]

Ok, searched but couldnt find exact answer...

Got an RB here sitting on a motor stand. I need to find out the condition of the motor, so im guessing since i cant compression test it, then a leak down is my only other option besides saying stuff it and rebuild it anyways.

Is it possible with the motor on the stand (how do i stop it spinning)?

No manifolds attached, just the bare long motor.

Anyone got steps / links etc to help me on doing this?

Cheers.

[GTRNUR]

You might be able to borrow a VL RB30 auto tranny bell housing and starter motor from someone. Thats to get it cranking. It wont spin over on itself and can be held by one person when cranking.

If your careful you can put some wood under the sump and prevent any rocking from damaging the sump. Ideally you'd use the engine mounts and a frame to hold the engine, but since your not starting it you will get away with it.

[SECURITY]

to do a compression test i managed to get around 70psi from turning the crank bolt by using a rachet while the motor was on the ground. i suggest getting a long breaker bar and try turning it. you need to get 5 uninterrupted revolutions to get a decent reading. you wont get a proper reading because the engine wont be at OT but it will give you a good indication on how even the cylinders are holding compression.

for the leak down, you can lock the cylinder at top dead centre (dont forget, each cyl has to be at TDC when testing it) by holding a breaker bar on the crank bolt. but because it will be at TDC the chances of it turning arent that great.

[Bl4cK32]

Well...seeing as its out of the car, there is no real way you can do a compression test. It needs to spin at cranking revs to get a proper reading. FWIW a fresh motor is about 150psi, and using a wrench on the pulley bolt is a little far from ideal.

Hence the leak down test, which i know pretty much how to do. What i wasnt exactly sure of was if it can be done with the manifolds off. I know you put each cylinder at TDC with the tester plug in (closes off the cylinder completely) then pump air in. Listen for air at either side (intake then exhaust) and dipstick. Why im also asking is because some say to pop the radiator cap off and look at the coolant to see if the head gasket is holding (bubbles)...

From anyone who has done one before or knows, is it possible to get a good reading with the motor out, and how do i get around the coolant issue?

edit/ I suppose i can just listen for leaks up the coolant passages the same as you would in the intake and exhaust (use a hose...one end in ear / the other in the area you are interested in) or i could hook up some long hoses to the coolant intake / outlet and throw em in a bucket of water and watch for bubbles...as for the motor not spinning, ill hook up a flywheel and put a flywheel lock on it to stop the motor spinning.

Edited February 13, 2011 by Bl4cK32

[SECURITY]

long breaker bar will give you the leverage you need to turn the motor at cranking speed - or thereabouts.

[GTRNUR]

long breaker bar will give you the leverage you need to turn the motor at cranking speed - or thereabouts.

I'd love to see someone try and turn over an engine at 250-300 RPM with a breaker bar. I think more likely you will bust your gut just getting 30RPM.

Piston rings dont close up till the engine is hot, so the leak down/blow by when cold would mean you'd be lucky to get 70psi.

[Bl4cK32]

I'd love to see someone try and turn over an engine at 250-300 RPM with a breaker bar. I think more likely you will bust your gut just getting 30RPM.

Piston rings dont close up till the engine is hot, so the leak down/blow by when cold would mean you'd be lucky to get 70psi.

Yeah, theres no way you can crank a motor over by hand fast enough to get a close reading. Leak down test can still be done apparently when the motor is out, but it will read a little more of an overall drop though.

What im after is to check the head gasket, and general condition overall, so if one cylinder is way off then i should be able to see...?

[SECURITY]

if you knew how to do a compression test you would know that you only need 5 revolutions to get a result. obviously the quicker you do it the better, but it can be done (i've done it) and you can get a reliable result. keep in mind you will not get a OT reading, but you are only looking to see that the cylinders are within 10psi of each other.

[GTRNUR]

if you knew how to do a compression test you would know that you only need 5 revolutions to get a result. obviously the quicker you do it the better, but it can be done (i've done it) and you can get a reliable result. keep in mind you will not get a OT reading, but you are only looking to see that the cylinders are within 10psi of each other

And there in lies the problem with your "compression test". Cylinder pressure attained in a compression test is a function of engine rotation speed and cylinder seal (rings, head gasket and valves). Any variation in speed means a variation in your results. This is why compression tests are done with a starter motor that can be cranked over continuously until a maximuim rotating speed is reached.

The only thing you can do with a breaker bar is position each cylinder at TDC for when you perform a leak down test using an air compressor and leakdown test tool.

Just because you've done something, it doesnt mean you did it the right way.

[SECURITY]

and just because you havent done it that way, doesnt mean it wouldnt work. like i said, your results arent going to be at OT but you can still check if they are within spec to a certain point. i mean if you're getting 90psi from one, then 70 from another using that method then you will know if its rooted or not.