compression check on a non running motor

[Miker]

Okay, so I have checked the compression with the guage thing screwed in at the spark plug while turning the engine over four or five times with the starter doing the work with the coil wire off and that really helped me understand my compression rates in each cylinder.
Now, can the compression be checked on a motor out of the vehicle with about the best spinning being a breaker bar on the crank shaft as quickly as I can do it? Or, is there another way to skin this cat?

 

[bknbronco]

I have seen guys start and even run a motor that was still hanging off a engine lift by the two chains! If all you have to do is turn it over a few times then do that. Please be careful, and take the fan off. I seen it run for a minute this way. They put a fuel line in a small gas can, put some wires on the starter, and let er rip!

 

[Madgyver]

As long as you got a bell housing on it with a flexplate/flywheel and starter, you can still test for compression using the starter. Be careful doing this. Make sure motor wont turn over on itself so strap it down.

 

[brewchief]

If you had access to compressed air you could get a leakdown tester instead.

 

[Broncobowsher]

Can't turn the engine over by hand to get a compression reading. You need a good starter and battery to do that. Funny thing, the starter doesn't bolt to the engine, it bolts to the bellhousing. Makes it a lot more difficult.

As mentioned above, a leakdown tester is a good alternative.

 

[TBS-POPS]

As mentioned above, a leakdown tester is a good alternative.

A leakdown tester IS the best way to test condition of any engine, running or not.

 

[Miker]

very good, Harbor Freight here I come for a leak down tester. Thanks guys.

 

[OX1]

I've done both compression and leakdown tests on cold engines. Never did get very good results (cylinder comparison wise) compared to a warm engine.

Obviously the numbers will be lower (or higher in case of leakdown), but I've seen wildly varying compression numbers that evened up quite a bit with a warm engine.

 

[hartbronco]

I have seen guys start and even run a motor that was still hanging off a engine lift by the two chains! If all you have to do is turn it over a few times then do that. Please be careful, and take the fan off. I seen it run for a minute this way. They put a fuel line in a small gas can, put some wires on the starter, and let er rip!

You don't need Gas or spark !!!!! just install the starter and roll the motor over 6 or 7 times on each cylinder with all the other plugs out . This should give you a good idea of what you have , with out trying to kill your self !! But it would be fun to watch you doing this ... take video LOL

 

[Steve83]

The engine needs to be warmed up, and if it has hydraulic lifters, it MUST have recently had good oil pressure to get the valves open. It needs to spin several times at speed to for HLAs to adjust.

 

[Rustytruck]

Pull all the plugs, spray some oil in the spark plug holes, wire the carb wide open and use a electric impact on the Damper to spin the motor. I saw a guy once rope start his Bronco on the trail with a rope around the damper pully. There are many ways to spin a motor.

 

[ochretoe]

Pull all the plugs, spray some oil in the spark plug holes, wire the carb wide open and use a electric impact on the Damper to spin the motor. I saw a guy once rope start his Bronco on the trail with a rope around the damper pully. There are many ways to spin a motor.

I have done something simular to this. Put an impact on fan nut and turn the engine over with the impact. Two or three turns is all you need for a pressure test. Be sure and pull all the plugs first and make sure everything is oiled. We used a squirt of 20 weight oil in each cylinder.

 

[Quick & Dirty]

I don't like the idea of using an impact wrench. The whole point of an impact is to tighten/loosen a fastener without spinning whatever it's attached to. You're just going to end up with 400ft-lbs of torque on the balancer bolt and never turn the engine over.

Back when I was young and dumb I put an impact on the nut of a rear axle input. Just the center section, not even installed in a housing. It turned easy by hand, I just wanted to watch it really spin. The impact never turned it at all, it just hammered the yoke into crush sleeve and locked up the pinion.

 

[bknbronco]

x2 on what quick and dirty said above!

 

[OX1]

Back when I was young and dumb I put an impact on the nut of a rear axle input. Just the center section, not even installed in a housing. It turned easy by hand, I just wanted to watch it really spin. The impact never turned it at all, it just hammered the yoke into crush sleeve and locked up the pinion.

HAHA, that's great!!!!

 

[Broncobowsher]

If you have an impact wrench that can turn over an engine, I want to see that impact wrench because it ain't a normal one.

 

[bknbronco]

If you have an impact wrench that can turn over an engine, I want to see that impact wrench because it ain't a normal one.

You read my mind!