Thanks for the replys, I haven't had a chance to measure the bore as we have been busy and out  of the shop. We hadn't used the tractor in a few years and would like to get it back into service. The 77's main work was grounding feed, running augers, and raking hay. I'm sure the tractor will return to it's former duties. Mainly augers and rakings. Will try to post tomorrow with more details.