why does a scooter crank have 3 sets of sprocket teeth on stator side?

[Iahawk]

as the title says...I recall questioning this when I had my motor apart earlier this year. A scooter crank has 2 sets of sprocket teeth on the stator side of the crank. The inner sprocket runs the oil pump...the outer sprocket isn't hooked up to anything. Can anyone explain why?

[rjs987]

Looks to be the same size... same number of teeth.
Maybe to "catch" the chain if it skips off of the inner sprocket? or maybe a backup if the inner sprocket wears out? Obviously wild guessing here.

My first bike was a Harley Davidson 125 cc dual sport bike, and AMF abomination. It had 2 sprockets on the rear wheel but those were different sizes and for the purpose of switching from road bike mode to trail bike mode. Thus the "dual" sport. This doesn't look like that.

[Iahawk]

you may be on to something with the extra sprockets being there to help keep the chain on its sprocket? Here's a better pic showing actually 3 parallel sprockets, but only the 'real' center one has full teeth. The other 2 sprockets have squared off teeth. The center sprocket drives the oil pump, so it is a pretty important one

[rjs987]

That was another thought of mine as well. That it is there to ensure the chain stays put.