It's not a small one,It's the usual size you put on a go Kart. I used a bore sleeve to up the shaft from 5/8 to 3/4,the driver clutch did not fit all the way down the key slot but more than half way,anyway it has not caused any problem in 3 weeks so I think it's good to go.I'm only running a stock 79cc predator so it isn't nearly as powerful as the 6.5 predator made for that clutch.I used a small bike I had no real use for because I had no way of knowing if the concept would work,it works great so I might eventually move it to a larger beefier bike. The engine mounts are just simple angle iron with c clamps . I put the angle Iron pieces about 4 inches in length in a vise and bent them inward to make up for the angle in the frame and seat post. I could move them up and down to get everything where it would work best.