Hi there.. This is my Mongoose m/b turned in to a recumbent .. I have mounted a Robin engine on the cranks, where the lower bracket was. I push the over center leaver forword, it locks the drive gear on the tire. I rode the bike about 500 miles before I put the engine on..The bike it's self takes a while to get used to, with the movable bottom bracket. I really like the setup..lots of fun this tinkering.. Take care Bill