This is topic Compression test on sitting engine in forum Tech Talk at Northern California Ford Owners .
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Posted by zpyro35 (Member # 3745) on
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A compression test should work on a sitting engine, right? I tried a compression test on this engine I just got, and the gauge showed nothing. I did hear, however, air coming out either the intake manifold or the hole where the distributor goes. Did I get screwed on the engine that I thought was good?
Also, what size bolts do you use to put the engine on a stand? Cuz my engine just fell off the stand...I tried rotating it and it sheared the bolts right off. What size bolts, what strength, and where do they bolt to? I had 2 on the lower corners and 2 on two other places that the tranny bolts to. I used 3/8"x3 1/2" bolts that were threaded the whole length of the bolt. the two on the bottom corners sheared off (actually one did....the other had the engine hanging off of it, bent the bolt at about a 45* angle.) the other two just kinda fell out.
Posted by st5150 (Member # 51) on
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Sounds like the piston wasn't at TDC. The intake valve was open and letting the air through. The piston has to be at TDC for the cylinder you're testing.
Posted by 87 Saleen (Member # 1549) on
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7/16"
Posted by mtbaughs (Member # 4052) on
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Wow that sucks...Like mentioned you'll have to use 7/16 bolts to set the motor on an engine stand. As far as measuring the compression goes I would do the following to make sure it is a safe thing to do. Drop the long block into the car with the starter and tranny in place. After all the valve's are set/ roller rockers are set with proper pre-load I would than hook up a compression gauge. Using a remote starter switch spin the motor for each cylinder. This will give you the compression for each cylinder. Hopefully with the motor falling like it did you didn't damage anything. Not to sound like an ass here but you may want to grab someone who has some experience in doing this as I think it might save you some time and more importantly a lot of money if things end up going together wrong.
Posted by zpyro35 (Member # 3745) on
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The problem with putting the engine in the car is I would have to take the engine out of the car that's already in it, then drop this one in, do the compression test, then swap it back out for the old one. and being my daily driver I don't have the time for that right now.
Posted by 88-383 (Member # 4088) on
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I may be with late with this info, but you can do a diffrential compression test on the engine out of the car.
Pull the rockers off so the valves stay closed then do a diffrential compression test. What you get is what you got! just let the piston settle at BDC becuse it wont matter. The chamber should be sealed.
Trust me this will work.
KM
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