cheap #25 casted chain drive+ clutch from 49cc dirt bike

I just got this from the mail :







It is a dirt bike gear down, quality is quite good. it has a clutch bell on the input (to be used with one of those : http://cgi.ebay.fr/ws/eBayISAPI.dll?ViewItem&item=150578306064&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)
and the output looks a lot like #35 pitch chain, but I think it will fit #219 with some elaborated machining (Angle grinder).
This thing is simple, well made, and ridiculously cheap : 25euro delivered 8)
It should handle 3-4kw easy, paired with a 63-74 on the input and a SS190-200 and 8s2p headways.

Some of those pocket bikes trans use straight cut gears that are noisy as hell and do not handle much torque, but I do not recall seeing many people try those ones?

Score. 8)

You don't really need a clutch w/ a brush motor, so I've got a single reduction w/ #25 sprockets/chain. A 7.27:1 to a 10" wheel with a 4500/6750rpm motor (cont/peak) produces roughly 18-27mph, which should be plenty for my cheapy pocket bike. It's got a pretty good low-end as well since 1000rpm = 4mph it's easy to pace a person walking w/o cooking anything.

i used the 5-1 ratio one on my recent build, i am actually modifying the bike to use one of those gearboxs you have there. But i have got one coming that had a double row chain drive on the inside for more reliability i suppose. Problem is if your using a clutch you kinda need to the rpms up at 10k to get it to handle more then 5kw of power otherwise it slips, but thats about where i wanted it anyway for my project.

Auto clutches are great if your using cheap brushless ESCs or you just want to remove shock loading from the system