I've always been told by my dad the cranks and counterweights usually come apart for people who never idle down once they cut the blades off and are just moving the mower around. Don't have to be full throttle for the motor to move I usually just have half throttle if the blades are off. Dad is a diesel/gas mechanic for 40+ years and has a degree. Been yelled at many times when I was young for forgetting to cut the throttle down but we got over 3k hours out of that Kawasaki. Engines don't like full throttle with no load on them.
Edit: also never just sit there with your motor going full throttle and nothing going on may hold up for a while but will eventually come apart on you.
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