Originally Posted by bandito
Theres alot of weight on those 2 frame stems that go to the back wheel from the crank housing and PERSONALLY I would not drill a hole in them, their not very big to begin with and to weaken one intentionally doesnt seem like a good idea to me. At least 50% of the weight of the bike and the rider goes through those stems plus with the vibration of a happy times your just asking for a disaster.
Totally disagree with this. Too many folks have done it with no bad results, me included. Have you personally experienced a failure due to drilling? A 3/16" hole through the chainstay will not compromise the strength enough to be a concern. The chances of a loose tensioner bracket rotating into the spokes are way higher than failure of the frame from a small hole.