Yes a bent valve, or push rod would cause low compression. Poor valve timing (from a skipped tooth) would also cause low compression. You're not only looking for low compression, but in your case you're looking for a difference between the two cylinders.
If you buy one, try and find an OTC. Unless you're going to go with a matco, snap on, etc. Then OTC is the best affordable specialty tool manufacturer.
When checking compression make sure the throttle is fully open and crank it over 4 times. I don't know about an FH780, but an FH721V's minimum compression is 57 PSI
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Last edited by CLS LLC; 10-08-2012 at 10:55 AM.