Re: Frame Reinforcement Issue
I'm not familiar with the Legacy Cruiser but the frame looks very much like the Jaguar and Southport cruisers which are very popular foundations for motorized bicycles. I have two Jaguars both of which have hundreds of miles on them with absolutely no evidence of metal fatigue or weld failures. Your weight is just a little over mine so rider weight isn't the problem. Neither is the shock of clutch engagement.
If I understand your original post you have a new Legacy and are looking for ways to reinforce it. I don't feel reinforcing the frame is necessary. I have to think you had a defective frame on your first bike. I have no idea where or why but that Schwinn frame design is more or less trouble free...in most cases.
By the way, your chain tensioner bracket will prevent a lot of problems. Good work.
Please keep us informed on your efforts and their results.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"