787 has 150psi and 120psi...can I run it ???

[gcha1727]

Hello. My motor currently shows 120 and 150 on a compression test. I read not to go beyond a 10% difference on the cylinders.

Will it damage the motor if I use it like this?

If it can be used will it be noisy or vibrate or anything else?

Thanks

 

[Dr Honda]

Will it run... yes. Should it run... NO !!

What ever cause that one jug to drop to 120 psi will continue to eat at it... and it will take out the crank. If you caught an issue before the meltdown... you are lucky. I would pull the head, and take a look. You may be able to just replace a piston and rings. BUT... you need to figure out WHY it happened. My bet is that the cab is plugged up, and I'm also betting that it's the PTO jug showing the low pressure. (It is more susceptible to a lean run)

 

[gcha1727]

Long story but Illl keep it short.

I bought a used motor with a missing piston. The cylinder/head looked good. I had a piston that fit well which brought that psi to 150. The original one is at 120psi. I suspect the 120 psi cylinder is old and almost at rebuild stage.

Does this info change your opinion on causing possible crank damage?
What will happen if I try to run it like this?

Thanks