Gears for CIMs

Does anyone know the best place to find gears for the CIM motors? My team is trying to build a gearbox with 2 cims, and we can’t find anyplace that carries metric gears.

Most large gear comapnies will carry metric gears with an 8mm bore to fit the output shaft of the CIM. However don’t be limited to just metric gears, as a standard gear with a bore a bit smaller will also do the job. I used a 12tooth gear from Small Parts (a Martin Gear) that had a bore of .313 which is just under the ~.315 inch conversion of 8mm.

For any gears, metric included, try,,,,, as good old


thanks, that helps alot

Fortunately, this isn’t a problem since the shaft size on the chip has a 0.313 diameter bore, which is the fractional 5/16". This isn’t a super-standard size (1/8 inch increments are easier to find) but they you’ll be able to compare a number of solutions at

I hope this helps,



The bore on the CIMs this year is an 8mm keyed shaft as per page 1, section 6 “The Kit”. While the spec sheet from last year lists it as .313 +/- .0004. Either gear will do fine, a .313 is just a tighter fit, and needs a little “coercing” to go on the shaft. An 8mm bore should spin freely on the shaft without any need for some help to be put on. I did this exact same thing on Thursday, so I am more confident in the kits listed 8mm.



I was just saying that if you can’t find metric gears or you don’t wish to use metric gears, you don’t have to. On 461, we’re trying trying to the standardize to English units. :slight_smile: