compression test with engine out?
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Racer
Joined: Aug 2000
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Originally Posted by C3w4sp
you wouldn't fire the motor to do a compression test with it in the car.
Would bolting up the starter & hot wiring it do the trick?
Anybody ever do this on an engine stand?
Pro
Joined: Jun 2005
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St. Jude Donor '09, '24
Sure can, get a pair of jumper cables and run 4 ga. sized wire to the starter motor and a small wire to the solenoid. Negative side of the battery cable to the block and both wires to the positive side of the cable. This should spin the starter enough to get your compression check done, houstonvett
Pro
Joined: Mar 2000
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From: NE USA
if you had an engine stand that bolted to the motor mounts, like a storage stand, speedway has them like 40 bux.
most engine stands bolt to the block at the bell housing bolt holes. the flywheel / flexplate will have to have clearence to spin. either way make sure its stable and seriously held in place, take all the spark plugs out. use a fully charged battery, reg up a switch between bat and starter, crank with gauge installed in spark plug hole untill you reach max reading. repeat all cylinders. VETDRMS is right the reading will be low but the key is consistancy from cylinder to cylinder.
dunno how dangerous it is, never tried it, dunno if it would need oil or not.
most engine stands bolt to the block at the bell housing bolt holes. the flywheel / flexplate will have to have clearence to spin. either way make sure its stable and seriously held in place, take all the spark plugs out. use a fully charged battery, reg up a switch between bat and starter, crank with gauge installed in spark plug hole untill you reach max reading. repeat all cylinders. VETDRMS is right the reading will be low but the key is consistancy from cylinder to cylinder.
dunno how dangerous it is, never tried it, dunno if it would need oil or not.
Pro
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St. Jude Donor '09, '24
Can do when taking the motor out with a Porta Crane or cherry picker. Just take the belts off and plugs out. One person should be able to keep the motor from moving around while turning the starter over. Would pre lube the bearings with an oil pump primer before spinning the motor, houstonvett
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Pro
Joined: Mar 2000
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From: NE USA
Originally Posted by houstonvett
Can do when taking the motor out with a Porta Crane or cherry picker. Just take the belts off and plugs out. One person should be able to keep the motor from moving around while turning the starter over. Would pre lube the bearings with an oil pump primer before spinning the motor, houstonvett
as long as you don't cover the intake with a lifting bracket, the reading would not be accurate.
Melting Slicks
Joined: Dec 2005
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Originally Posted by tonyk72
Doh!
Would bolting up the starter & hot wiring it do the trick?
Anybody ever do this on an engine stand?
Would bolting up the starter & hot wiring it do the trick?
Anybody ever do this on an engine stand?
Sure it's doable. You can test fire, break in a cam and check for leaks on an engine stand, I did this on a fresh rebuild. You need to take the precaution of bolting it down to the concrete floor though. you wouldn't want the rapid spin up of the reciprocating assembly to cause the motor to do unwanted acrobatics if you decide to fire it. Spinning it with just the starter could be done without securing it.
And a compression test can be done on a cold engine.
Originally Posted by C3w4sp
as long as you don't cover the intake with a lifting bracket, the reading would not be accurate.
Last edited by shafrs3; Mar 16, 2006 at 08:36 AM.
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
test: leakdown v. comp
Those are all good suggestions for a compression test.
However, you may find doing a "leakdown" test will yield more info and is easier to do on a stand. The leakdown tester is similar to a compression tester but the leakdown tester has TWO gages on it ... and it attaches between your sp hole & a compressed air source ( compressor). You don't spin the motor with a starter, you can do it on a standard engine stand or while suspended from a cherrypicker, you don't need a carb or intake or exhaust. With leakdown, you push compressed air into cylinder ... not pumped up by a spinning motor. Moroso as well as many others sell a leakdown tester. Probably about $50-$80.
However, you may find doing a "leakdown" test will yield more info and is easier to do on a stand. The leakdown tester is similar to a compression tester but the leakdown tester has TWO gages on it ... and it attaches between your sp hole & a compressed air source ( compressor). You don't spin the motor with a starter, you can do it on a standard engine stand or while suspended from a cherrypicker, you don't need a carb or intake or exhaust. With leakdown, you push compressed air into cylinder ... not pumped up by a spinning motor. Moroso as well as many others sell a leakdown tester. Probably about $50-$80.