Friction drive lawnmower engine

[Jasanabia]

My friend wants to put a lawnmower engine on his bike, here's the design we cam up with,
The vertical shaft engine bolted to a rear rack with the shaft rubbing against the side of the wheel. The only problem is there's no clutch, is there a solution?

 

[ducedave]

My friend wants to put a lawnmower engine on his bike, here's the design we cam up with,
The vertical shaft engine bolted to a rear rack with the shaft rubbing against the side of the wheel. The only problem is there's no clutch, is there a solution?

pivot the motor engage disengage or use a syntrifical clutch