I got a free one wheel peel go kart, 3.5hp Briggs, my daughter was riding it and after about 30 seconds it threw a chain, the wheel side with the sprocket on it fell off, I found the nut but when I put the wheel and sprocket back on the threads on the axle are flush with the outer bearing, what can be wrong or what am I missing? I'll get pics tomorrow if that will help, just want to get this figured out for the kiddos if I can. Thank you for any advice.