787 engine loses compression on compression tester but starts and runs?

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JKSTI&R1

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Hey Guys,

So had a quick question. So i got in a couple 96' gsx and they both had the same problem. One ski was running and did start and run. So i went to check the compression on the engines and it got up to like 145 bouncing hard 20 psi and as soon as I stop, it went from 145 to zero in a few seconds. I could hear it coming out the manifold. turn lights off, used flashlight and could see the gases. So is it the crank case seal? Ive never had a motor do this, let alone 2 of them from the same person. The other motor went to 180 psi because it does have a seal leak and had some oil in the cylinders. It also went from 180 to zero in a few seconds. So if this is the case, is it normal for it to run? the motor with the 180 psi was never running, had parts missing off it............

Just curious your guys thoughts on this. Either way, both will be parted out and not sold as a good running engine.............
 
What do you mean it goes to zero? My compression gauge holds the highest psi until I release it. The engine doesn't hold the psi when you stop but the compression gauge should.

145 is good, 180 is a little high, but will likely drop some after running it a bit.
 
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