Is the sound you hear really grinding or a chattering from the starter solenoid? There are several things. Your adjustment may have slipped, did you turn the engine over a couple of times and check the adjustment again? Did you check that the rocker arm stud was tight in the head? Did you check that the rocker arm was not cracked thru the stud hole is where this would usually happen. Have you removed the spark plug and tried it? Might be hydro-locked from leaking carb float. Could be cable connections.

Walt Conner

It's a grinding noise