[Tinker51]

A friend had this very same problem in a fairly potent hi-po 289 he built. The gears would last about 1500 miles then shear the pin. We looked at all the same things you all have suggested (brass gears, larger pins etc.) but they each failed as if on cue at around 1500 miles. Mr Fixit and Excaliber have it though, the gear was too deep and was under pre-load when the dist. hold down was tightened but it was so close you would never see it (plasti-gauge confirmed it). Next gear was a stock steel gear which we machined some material off (I don't recall now how much) and it has run like a beast since.