I have built two motorized bicycles now.Both of them have 49cc 2 stroke engines made in china. I decided i want a 4 stroke. I asked the man at Toys4Boys Motor-sports about his 4 stroke bicycle kit. He said "don't do it. It is gutless and a pain to install. Not recommended." This left me with only one option. I must build one from scratch. I went out and bought a brand new Briggs a Stratton weed whacker engine. I also bought a 1981 Raleigh Challenger. Now it shouldn't be too hard to put them together right? This is what i have to work with. The roller is something I machined in my garage. It is one solid piece. I milled one side square to match the weed eater drive shaft. I pressed a bearing on the other side. Tomorrow i plan on mounting this all in a housing and somehow attaching that to the seat stays. Let me know what you think, any ideas?