That is a GY6 engine.They can be surprisingly well made if you get one from a reputable vendor that sources them from a good factory.
In a similar fashion to the HT engines that are so popular with MB's, GY6 engines are made in many different factories and alot of the internal parts are not interchangeable between them. It can be a real PITA when trying to source replacement parts.
Also like the HT engines, there are good GY6 engines from good factories and bad GY6 engines from bad factories. I am talking brand new still in the box good and bad.
There are quite a few members here who have made similar builds to what you are asking about, but I have seen none so far that have used a GY6.
See this thread for more info: http://motorbicycling.com/showthread.php?t=44313