0pyders

iTrader: (3)

Can you do a compression test without the intake manifold installed? I'm trying to make sure that my cylinder heads are sealed good so no coolant leaks.

zraffz

I don't see why not. The intake manifold only covers intake ports on the heads. You technically are supposed to test compression with the tb/primaries/secondaries wide open anyway.

AlkyIROC

Since very few people know to open the butterflies while doing a compression test, it's probably better to do it without an intake manifold.

The only drawback may be if there's still coolant in the block. Just draining the rad to remove the intake doesn't remove the coolant from the block. With the intake off, coolant may spill into the lifter valley and get into the oil.

0pyders

iTrader: (3)

no coolant, the engines on the stand. Would it be okay to test it without oil in the crankcase since it's just a few spins?

74Novaguy

You would be better off doing a leak down test than a compression test. you wont beable to spin it fast enough to get a good reading. and a leak down will tell you if seals are leaking.

zraffz

Why can't he bench test the starter on the motor without any plugs in it or belts on it?

And double check with Alky but you should be fine cranking it without oil in it. Most guys I know don't prime the oil pump on rebuilds; doesn't seem any different to me.

74Novaguy

I guess i didnt think about putting the starter on it on the stand... I guess I would make sure your stand is secure. If your doing all the cylenders I'd put oil in it. Ive put motors in with out priming them before and no problems but im not cranking them very much before they get oil from the pump and they usually have alot of assembly lube. And hes also looking for leaks... its easier to find leaks from a leak down test because you can keep pressure in the cylinder while it leaks down.

0pyders

iTrader: (3)

I'd do a leakdown test but I don't have an air compressor. I think I'll just fill it with oil to be safe and just make a mess and do the test. Thanks for your help guys.

zraffz

I've went as far as firing a motor up on a stand, had oil in it but no coolant and no hose supplying water. I did have the motor mounts on it though with a ratchet strap holding them down to the base and two jack stands with a 2x4 under the front of the oil pan though.
I've also seen a big block get fired up inches off the ground.

AlkyIROC

Filling it with oil won't help. The oil pump is driven by the distributor. Without an intake manifold, you won't have the distributor installed.

1969RSSS

i would use a primer rod and drill on the pump drive or a pressurized oil tank line into the rear oil plug. Rebuilt and installed over 2000 engines and i would never do this without some sort of oiling. When you are checking the compression in a given cyl you are adding that load to the rod bearing and adjoining main bearings with no separation between the crank journals and bearing surface not to mention dry cyl walls after 3-4 cyls tested. So i would at least put oil in the pan for some splash lubrication and give the oil pump some spins to lube the cam bearings and lifters.
I think a leak down check with a pair of chassis ears with the rod taken off and the hose end inserted into a coolant passage would be about the most accurate test your gonna get.
You could also install the intake and water pump, install some looped hoses and pressure check the cooling system would also work. Either way good luck with your build.

RyanEricW

Make sure the engine is primed or your readings will be off. Maybe some do not know it, but oil actually helps in the sealing of the rings..

Also if you are running an aluminum block, you need to make sure the block is at operating temp, or have specs for a cold engine, as aluminum expands more than cast iron. This may be arguable, as usually the pistons are aluminum as well, so they are supposed to expand/contract together.

There's a special tool for priming the oil pump with a drill....run it for 5-10 minutes, or until all of the valves start oozing oil before you do the test. Cyl leakdown would be nice as well.

ItzPerfect Bos

it doesnt matter if the engines in the car , out the car. Intake on or off. Starter or by hand. Leak down test is a good test but not one you can do in ever situation. Compression is compression. weather you pmuped it up by hand ( turned the engine in a complete revolution). Its the same. It doesnt matter how fast it turns. The speed has nothing to do with the compression. Thats incorrect.

74Novaguy

Way to go reviving an old thread
Actually turning by hand will lend you a low reading on a dry compression test due to air leaking past the piston rings. May get a better read with a wet compression test. But still with the slow turning by hand you will get an inaccurate reading. you can however bolt an started to the engine on the stand and turn it over with a 12 battery.