Idle Pulley Torques Inward

[crassius]

Another thing that can put excessive force on the tensioner is of the tensioner isn't aligned to feed the chain straight up onto the bottom of the rear sprocket, the chain can miss the teeth and wind around the outside of the sprocket (which makes it WAY too short).

[maniac57]

The tensioner takes the most abuse when starting a new, tight engine. Do whatever it takes to secure it before you get hurt. Twisting to line up the idler wheel better and tack-welding the tensioner should cure your problems. If you decide to weld it, be sure it is positioned to give you the most range of adjustment in the chain BEFORE you weld it.

[VTHokie]

I ended up adding a tensioner that is bolted to both bars, and it feels extremely sturdy. I got the idea from the thread provided earlier (http://motorbicycling.com/showthread...ight=tensioner).
I gave it a test ride today and it held up superbly, but due to my inexperience in balancing the rear wheel, I blew apart my coaster brake and lost all the bearings. BUT, the tensioner held up perfectly, and I'm extremely happy with it.
Thanks for all the advice and suggestions.
Here are some pics:

[GearNut]

Good job with that tensioner!
I am sorry to hear that your hub blew apart.
May you have better luck with the new one!

[VTHokie]

Thanks for the examples, GearNut. Those cushion clamps are priceless - I bought a variety in case I need them for future work.

[crassius]

Originally Posted by VTHokie

but due to my inexperience in balancing the rear wheel, I blew apart my coaster brake and lost all the bearings.

thought it might be a rear sprocket problem causing all that force

new tensioner looks good & solid, but I'd guess the old one would work when your sprocket gets fixed

[VTHokie]

Ahhh that's an interesting point, and it makes complete sense. I'd be lying if I said I didn't notice a significant wheel wobble, but I selfishly wanted to get the bike up and running before I worried about it -- lesson learned. I'm sure you're absolutely right, and the wobble torqued the tension bar out of place every time. I should've gotten that dang wheel balanced to begin with. After watching a video on tightening / loosening the spokes, I realized that adding that rear sprocket probably threw everything out of alignment (because the bike itself was brand new and would be in no need of truing under normal conditions). Hopefully I can find a place to put it back together today