The first bike I had was a nightmare after the bolts in the front mount broke one morning on my way to work, I noticed something touching my leg and looked down to see my motor moving side to side, as soon as I pulled the clutch in the whole motor jumped off the frame and locked the bike up at 25mph. (left me stranded at 4 a.m.in the middle of a long dark back road) I do wear a full size motorcycle helmet when I ride in case of such an event. I skidded to a stop and assessed the damage. My chain was twisted up and the bike was out of commission. I fabricated a motor mount out of two 2x4 ties and that worked like a charm. My first bike was a beach cruiser Electra. This one I've clamped the rear mount to the seat post first and made sure the front mount was touching the frame. I just put this bike together and want to know what you think. The motor doesn't budge and I've only tightened the nuts down enough to close the lock washers and a pinch more
Personally, what I do when I'm mounting a chinagirl, is I make my own mounting plates so that the bolts sit at the correct angle. I take some steel plates and drill some holes in them so that I can bolt the steel plates to the motor, and then put U bolts through the plates and around the frame.
It looks like the front of the motor could chew through your frame. The way Necromancer describes is a much better way to go. If you do follow his method get the ubolt that has the curved "bracket" and put that in the bottom of the U so it rests against the frame at the front of the downtube. It spreads the load out better than just having the ubolt itself against the tube.
This video shows what they are saying at 9.45 in. The offset flat plate method with the muffler clamp disperses the load. The flat plate can be clamp up or clamp down.
https://www.youtube.com/watch?v=kyWNS0xhG5g
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https://www.youtube.com/watch?v=kyWNS0xhG5g
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