by bgsengine » Wed Mar 11, 2020 9:41 pm
the correct bolts would typically be a grade 3 , or grade 5 with shear points grooved into them, but the simple action of the bolt shearing can make the surface of the bolt very very hard to drill... but what I always did was drive them through with a drift punch and heavy hammer, long as the auger and the shaft holes actually are still lined up.. but if someone put in an ordinary regular hardware bolt, chances are the bolt "bent" into the shaft as it sheared, wedging it into the hole. I never even bothered trying to drill them out if they won't come out with a punch and hammer.. one time we used a oxy-acetylene torch and actually drove the bolt far enough out one way that we were able to cut off the other end (with the "bend" mushroom") with a abrasive cut-off wheel, then drove the bolt back through from the freshly cut side.. but the extensive labor time, once we figured up the cost in labor (if we'd actually billed the time) , would have cost more than just replacing the whole gearbox... although I suppose, if you were to pop out the gearbox, you could then hammer off the augers and mount shaft in a vise or drill press, etc, and get the old bolt shanks out by other means..
How poor are they who have not patience. What wound did ever heal, but by degrees? - Iago (Othello Act II, Scene 3)