I fought a hard starting tractor for a couple of years. The starter would grind away at the ring gear without meshing. I even split the tractor and reversed the ring gear to have a new start on things. That didn't accomplish anything. I bought a new starter from the local automotive electrical repair shop that had been in business for half a century and had seen nearly everything. That didn't work either. In fact, the front housing of the starter cracked after just a few attempts. I researched and read all that I could on this particular tractor for months and finally got my answer. My tractor was a gasser and someone, prior to me buying the tractor, had put a starter for a diesel engine on. I had been repeating the mistake by matching the new starter to the old.