Re: What's the real reason for Chain Tensioners
I'm running an old Schwinn Mesa Runner mountain bike without an idler. To do so I had to modify the chainstay a bit. I cold formed a piece of 3/32" x 1" x 6" to fit the outside of the chainstay and welded it in place. With the torch I heated the inside of the chainstay tube in the area where the chain crosses and dented it in so the chainstay is about half its normal diameter in that area. A little bondo to fair edges in and some primer ande it looks pretty good. I haven't painted the bike yet but so far there's no marks in the paint on the chainstay from the chain. It sure runs more quietly than it did with the idler. Luckily the bike has nearly horizontal drop outs and a seven speed freewheel so there's only one chain to tension. I've ridden the bike about 120 miles so far with no problems. The only thing I would do different now would be to find a bike with V brakes, the old side pulls take a lot of pull with a double cable lever. I ended up extending the lever a couple inches for more advantage. It's working okay, but would be better with anything other than the side pulls it has.
I'm working on installing a four stroke on a cheapo mountain bike. I welded a 1"X1" square tube to the frame above the bottom bracket to attach the engine to. It looks like I might be able to eliminate the idler on this one too. If not I'll weld a strap to mount the idler so there's no chance it can move. I already experienced the 'fun' of having an idler drop the chain and lock up the rear wheel. Dirt bike experience helps with that but I still got dumped.
Goldwing 1500, Silverwing 600, Schwinn 49