These engines were originally designed and built by Ryobi. I have seen trimmers labeled Cub Cadet, MTD, and Troybilt (as well as of course Ryobi) that are essentially identical and use this same engine. I have owned and used a couple of Ryobi labeled trimmers. They start easy and run fine but are not very powerful. They are an interesting exercise in manufacturing efficiency - i.e. cleverly and cheaply made. They are built to perform their function as a home owner quality trimmer at the lowest possible cost.
I have not measured it, but I believe these trimmers have a 56mm clutch. Another issue is that this engine has an overhung crankshaft, with an output shaft on only one end of the engine. As such, the starter is between the engine and the clutch.
I am quite sure you could build a motorized bike with one of these engines, but unless you already have one (and lots of skills and little money), I think you would be much better off starting with a Honda GX35 or Subaru EH035 if you want a small 4 stroke.
Edit:
Just a tease, but I have a virtually new one of these engines that I'd sell for $45 plus shipping - if you are really intent on trying to use one!