starter clutch lockup

[aerowerks]

So I have this '75 CB500T. I bought it many, MAAANY years ago. It was my first bike. I rescued it from a junk yard. The only reason why it was being scrapped is because the starter clutch locked up while the engine was running. That oversped the starter and completely destroyed it.
Back then, I replaced the starter, and it was fine for a while. Then it happened again. I got mad, pitched the starter and just kept it as a kick start.
Now that I'm putting it back together, I'd like to know couple things:
1) why did it happen?
2) is there a way to prevent it from happening again?

 

[ancientdad]

Hard to know why it happened, and it's an odd occurrence that I've never personally seen before. The typically slip more often than anything else and the design is one that pretty much eliminates the possibility of lockup unless maybe something was assembled wrong. This is one of those instances, like so many, that pictures of it just as it was when you pulled the alternator rotor would be interesting to see.

 

[LongDistanceRider]

It's a sprag bearing that allows rotation in one direction only, locks in the opposite direction. So the problem could be related to Items 2, 3, 4 or 13 in this fiche. https://www.partzilla.com/catalog/honda/motorcycle/models-with-no-year/cb500t-a/alternator Until it's apart and inspected there's no way to know.

 

[crazypj]

I've seen it happen for couple of reasons,
1. someone pressed starter button for 'extra power'
2. damage to the ramps or flats on rollers
If ignition timing is too far advanced and you get a backfire, I've seen the ramped part (part 2 in diagram) actually crack and poke through the outer steel shell.
It's also possible for the plungers to be stuck if the springs get weak/old (parts 3&4)