[JSchmitz]

Hardening is a touchy thing. More isn't necessarily better. A lot of people assume that Grade-8 bolts are always better. They are better in tension but nut in shear. Learned that at a very young age. Put Grade-8 bolts in a Brush Hog drive shaft. They broke immediately. I played around with Cherry Red powder hardening compound in the machine shop. I made a T-bolt for the lathe compound rest (just playing around). I hardened it with the Cherry Red. It snapped as soon as I started tightening it. It was made from good quality high carbon steel. If you start with crappy material, no amount of metal conditioning is gonna produce a good product. I suspect this to be the case with the oil pump drive shaft in question here.