I'm sure there's probably a simple solution to this, but I couldn't figure it out this morning. The cog on my old chain tensioner kept coming unscrewed and then the chain would come off. TerraTrike sent a replacement, and I installed it, thinking I had it right but then when I tried to ride the tensioner swung forward and the chain slipped off the hub. It seems like the chain tensioner is screwed on tightly, but it can still move forward. Clearly something is wrong. Any suggestions? I just don't see what else I need to do to fix this.