So, the spring in the Surly singleator that I'd been using on my SS is completely shot. I'm not really sure how it happened, but it seems that the spring, which is essentially a corkscrew with two very short 90 bends at the tips (these create pins that fit into holes in two parallel plates to hold the tension on the chain), is stripped out of the holes that hold it in place, meaning that the tension is gone off the chain. I've talked to a few friends about the possibility of using a regular derailer and just messing with the limit screws to get my chainline straight again. This seems like a reasonable idea to me.
The quesiton is -- should it be an MTB derailer or a RB derailer? The chain is an SS (BMX) chain and I have a BMX cog back there. Is an MTB derailer better suited to the heavier chain? Is an RB derailer too narrow to accomodate the chain? Which is going to hold up better? I'm really disappointed in the singleator; I've had it lest than six months and it's already shot (no crashes, abuse, etc.). Whatever. I'd love to get rid of the problem with a set of horizontal dropouts, but that's not to be (and free bike frames converted to singlespeed are gift horses, and not to be looked in the mouth).