View Full Version : JD compression rates

08-18-2016, 06:58 PM
I know there are many variables and I don't know what internals are in my JD but can anyone tell me the normal compression rates for the JD? Mine started running bad and when checked I got 25 psi out of the rear cylinder and only 15 psi out of the front cylinder.

08-18-2016, 07:12 PM
Sounds very low. You should have at least 75 psi. Confirm your guage accuracy.

08-19-2016, 07:38 AM
My racer, runs about 55 to 60 lbs warm, with an original iron piston/rings and tapered bore, since I built it about 5 year ago. Try lapping the valves, and the intake housing.