terrible grinding sound

[BrianG]

Hmm, the ebay listing says it's designed for 8th scale conversions, so it should work if they're telling the truth.

Yeah, the one on the left is a CB. The right is the kind Mike used to sell a while back before he started selling his hardened steel version shaped a little more like a CB.

Easy way to tell if your gear is ok is to roll it across a spur with the pinion not mounted. It should roll smooth without catching. If it catches, it's the wrong type. Still, a vid showing how it sounds would be helpful. I'd hate for you to go get different pinions just to find out it's something else.