You guys know that I am not an engineer -with that being said take this with a grain of salt.  I was looking at buiding a chain drive (motorcycle chain) for my minimax  (40HP Kawasaki) and found that chain does not like high centrifugal loads.  When you use a large enough crank/drive sprocket (13 -15 tooth) to minimize the turn angle you end up with a fairly large driven sprocket (39 - 45 teeth); thus the chain loads around the larger sprocket are suprisingly large.  I no longer have the calcs or I would share them.  I would love to find out that I made a mistake though.  Remember that a motorcycle has a primary gear reduction to reduce this RPM before the final drive.  It is intersting that some motorcles use a chain primary reduction - however, on my Maico dirt bikes these were somewhat short lived (200 to 300 hours).  Anyway, please run the numbers before doing this.  Lastly, I suspect that this would work OK with a short chain  that was changed often (only experimenting will determine how often) and I may yet attempt this if more research were to show a higher chance of success but my initial research was not promising.

Ken Powell