Originally Posted by bro-die
I recieved one as a gift... "how do I find out what displacement is my engine"
If I read you correct you are saying you don't know exactly what motor you have? If that is the case I guess a picture or at least a description of your motor would be needed to even start...
It also seems you were given a complete motorized bike, AND are going to build a second one??? If this is the case, do you have the motor for the second bike already?
Finally, you say you are a "heavy guy", how heavy?
Your post was a bit too vague to help you, fill in the details a bit and we will try to help you out....
Other posters have given you good advice already, but more specifics would help us give you more specific advice....