i know that people around here ride the smaller cc bikes and are always replacing rear rims because the drive sprocket runs off of the spokes that were never made to have torque on them ... if i were going to build one i would mount the engine over the rear tire and make/buy a unit that drives off of the rear tire, not the spokes

Yea my plan was to replace the rims with ones that are solid (more like a car rim.) I wonder how well a friction drive would work? Be easier but I wonder how handling would be affected? (Higher center of gravity....)

I use firmstrong frames. For the 212cc use the Chief frame it will give you plenty of room for the engine and a nice long wheel base making it more stable at speed.. I know people that have used this frame and the 212cc for racing. Got to over 100 mph with it. Of course for those speeds ya need speed rated wheels and tires. Yes upgraded wheels make it safer. Thick spokes and double wall rims. Some guys use moped wheels to get speed rated. You can not power a 212cc bike from the spokes. It will tear them clean out. You need to use a jack shaft. And you have to drive the rear wheel with a sprocket. If you dont know how its done let me know and Ill fill you in. (hint think disk brake hub)

Friction drive with a 212cc is not a good idea. It will make your tire bald very quick and when it gets wet it slips. You want to drive it with a jack shaft and a strong sprocket.

sprocket is not the problem, it is what the sprocket goes on

The sprocket goes on a disk brake hub. Use a sprocket instead of or with the disk. My setup uses a adapter I made to use with a disk and a one way sprocket so the pedals dont spin when your riding. One side of the hub you peddle with. The other drives the wheel.

I've ridden a few mainly the 66cc marketed as 80cc but a few bigger. Unless you do some serious stuff to them like Merlin has they are supper sketchy scary. The tires / rims and brakes seem to make the most difference but having a good suspension and drive train would be a big plus. I knew one nut who put one on a fixed gear. It did not last long.

Haha that sounds super "safe".... This will be a fun project....

Thanks I got it all figured out, or at least for tonight I do....

How hard do you think it would be to get rid of the pedals all together?

That is the easiest way to go. Here is a forum that deals with this stuff:
http://motorbicycling.com/index.php

Thanks man that seem like a cool site I will have to look into it more! With next pay check I will get my victim....:)

A lot of people are building bikes with the 212cc engine over there. There is thread of mine somewhere over there that shows my build. oldtimer54 is the nic on that site.

I am thinking I am going to stick with the 250, may have to scrounge for some stuff.... i.e. A transmission and some sort of engine:P JohnDoe on there as well.... I will look into your thread.

That would be kind of fun putting one of those bikes together. I would possibly try it if I wasn't on a steep hill with a highway to ride on to town.

In other words if I was in town I definitely would.