For spark ignition engines, the cranking motor should be used with the battery in full charge condition. Ignition wires must be disconnected from spark plugs in the case of spark ignition engines. Throttle should be set in wide-open position to provide normal volume of air to cylinders for correct reading. Spark plug should be removed only from the cylinder being tested to allow applying of the gauge. Removal of both spark plugs would result in a faster turning speed and, thus, a higher compression reading.
Model A
Cranking Speed 190 rpm
Pressure
A (All-Fuel) - 81.8
A (Gasoline) - 117.5
Allowable variation on No. 1 and No. 2 cylinders up to 10 %.
From John Deere field service bulletin 181-S, July 1951.
Try doing a compression test again after squirting some oil in cylinders and see if it comes up. If it does you may have stuck rings or a tired motor. If it does not you may have valves out of adjustment. Just a guess since it is a 48 it may still have the All-Fuel pistons in it, but 50 psi when it is suppose to have near 80 is not good.
This post was edited by Rodney51Cub on 09/19/2022 at 07:32 pm.
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