I have a Rigid ol50135w compressor and the motor sometimes hums when I turn it on. When it does run the compressor shuts off and hums when it get to about 100psi. I took the cover off and tried to turn the fan and it seemed hard so I removed the connecting rod to see if the problem was between the rod and crank shaft. There is some scoring on the rod and I attempted to fix that but when I put it back together it ran for about 10 minutes and started having the same symptoms. The oil is fine and I lightly sanded the inside of the conecting rod to smooth it...Any Ideas??????