I finally got around to putting 89mm cranks (kottered) on my old Frankenstein 24" Uni.
Bent the right one on the first freemount.
Very little money buys cheap components. (Cheap=crappy)
Those little suckers must handle an unusual amount of torque to start (and stop) a unicyler.
Re: Cheap little 89mm
Was it because of the freemount itself or did the freemount fail and you dropped the uni on a hard surface? Either way (but especially in the first case), I’d say this is a manufacturing error and you should get a replacement or your money back. No matter how cheap a crank is it would have to be capable of handling a normal drop, let alone a freemount.
I assume you bent the crank in which case the crank is to blame. If you bent the cotter pin, it might be that it was not properly mounted (in which case you are to blame).
You may be right about mfr defect. I just mounted and pushed with my right foot and zammo! That sucker bent right over. I was able to muscle it back to pretty dang close to normal with my bare hands. (I’m not no he-man)
Just crappy weak metal.
Your average 89mm cottered crank has a high probability of having been intended for a juvenile bike. Thas is, a bike ridden by a very young person not exceeding, and probably way under, 100 pounds. Even an replacement crank of the same brand may not last very long…