After exploring just about every single engine option, i am very curious about the 125cc dirt bike engines. You can get them with everything you need to run it for around $250. I can make mounts and brackets. I was wondering if i would have to run a jackshaft to get the proper gear ratio, and if 41 or 415 chain would fit on the engines 420 sprocket. i know this would be alot of engine for a bicycle, but i intend to run it cautiously. I also know that it wont be street legal, but i only really use the bike in my neighborhood, which is large and very hilly, so its not a problem.