Re: Bottom crank jack shaft.
Unless you have a pull start, you will need to lock up the freewheel. This can be done by taking off the seal/shield and filling it with solder. If you need a freewheel, I think a bmx one would hold up ok. Try to find a good one, look up the models you have and find out which is strongest. They can handle quite a bit of torque. Oh, and hankman, HP is torque times rpm. Torque is converted to rpm and vice versa. HP is what really matters, torque means nothing without rpm.
some people say that a motorbike defeats the purpose of a bike. i tell them to get a flintstone's car.