just shave the shaft of the kb. grip it tight with some sandpaper, run it, and check often for fit. people have also used a dremel cut off wheel, ran the motor and moved the wheel up and down the shaft until a pinion fit. people are always afraid to grind on shafts, which perplexes me. they'll launch the motor off a ramp at 60mph, but won't grind that precious shaft! it's just a hunk of metal, it won't even get mad at you!
