Two motors I've pulled apart have had this issue. I'm thinking on my next build to slot the crank all the way down and use straight key-stock instead of the half-circle woodruff key they use stock. The balancer bolt would keep it from coming out the front.
i did that on my GZ motor. a few minutes on a mill and a key stock from fastenal, bam problem solved now a can run an over sized crank pulley with no worries