So, you pulled your motorcycle starter apart, to replace (brushes) or rebuild something, and now that it’s back together it turns great but the bike doesn’t crank over.!?
It’s spinning the wrong way, because you put the “can” in backwards. Because it is going the wrong direction, the sprag clutch isn’t engaging and the engine isn’t turning (fortunately).
At least that’s what I just did/found. I’m writing this up in the hope this helps someone else.
By “can”, I’m referring to the middle part of the starter with the permanent magnets. Basically the shell of the starter is a cylinder (can) with two caps, in my case, one cap has the brushes, and the other end has the bearings that support the splined output shaft. It’s not that the can is 180 degrees wrong around the rotor, but that you got the brush/output ends backwards. I’m kinda shocked that it went together the wrong way. I couldn’t find the index marks on the can, but that was because they were faint and in the “wrong” place. Once I put it together the right way, all the index marks lined up (duh).