The only consistent problem I have with this old machine is with the way the final drive sprocket is pinned to the shaft. It is supposed to be a solid 1/4" "groove pin" but that had sheared. (Probably why I was given the machine....) I have been using grade 8 1/4" bolts, but these only last a few hours before shearing. I've been assuming these are at least as strong as a groove pin but maybe I'm wrong about that. I've been thinking about drilling out the shaft and sprocket for a 5/16" or 3/8" pin or bolt but that would be a bit of a pain. Suggestions? Is this a common problem with these machines? Thanks.