Rayon you mentioned cost factor & going belt drive & doing it right won't be cheap. I find chain breakage, even the low quality 415 chain shipped in the kits, to be uncommon. I've built a lot of motorized bikes over the last 10 years and have never broken a chain on the motor drive side and that includes several that used the chain in the kit. I feel you may have a chain/wheel/sprocket alignment, chain tension or chain installation problem. If one or more of these problems exist the chain undergoes strain that it was not designed to withstand. If you switch chains to a premium Diamond brand this will help and like Curt suggested if you use a 410 premium chain it's way stronger still and will cost much less than redesigning the drive to belt and may solve your problem, but simply getting everything straight, true and correct on the install is crucial and many don't take the time to get basic things right in their haste to get the bike up and running...big mistake... small things matter.
A few details. Buy a good chain and a quick link; the closed end of the link clip is installed to run forward in the direction the wheel turns under power while the open end follows. Do it backwards and the clip will come off and so will the chain.
The chain line has to be perfectly straight between the two sprockets, if not the pressure on the chain is greatly increased and wear on both chain & sprockets is increased while performance suffers. A quality chain breaker is your buddy if you know how to use one.
If you use the kit provided rag joint the adjustment to achieve a straight chain line is harder to adjust than with a three bolt sprocket adapter. Plus inexpensive bike spokes are easily bent during the installation and running of the rag joint which causes the wheel to wobble & can cause a chain the break & ruin a wheel.
If the motor isn't mounted straight & solid in the frame the chain won't run straight. There's a lot that can cause a chain to break that is just caused by poor installation technique.
If the rear wheel isn't centered and running true the wheel wobbles during rotation causing both side to side pressure on the chain and also chain tension problems as. I've seen guys check chain tension at one spot and it's 1/2" movement at midchain and call it perfect, but rotate the wheel a foot one way or the other and it would be so tight that it was hard to turn the wheel any further by hand and be so loose at other points of rotation that the chain was close to falling off ...this is terrible wobble tension caused by extreme wheel misalignment. Wheels have to run true no wobble. Chain tension has to be perfect and with chain lines running straight, not at an angle. In biking with multispeed cassettes cross chaining is an extreme example of what I'm talking about and as any experienced biker knows pedal chains can and do break under just pedal pressure when cross chaining occurs.
Running a spring loaded chain tensioner, properly installed, is a time and headache solver when running chains on both the pedal side chain and the motor side chain, but shouldn't be used as a substitute for good chain drive installation.
Of course you may already know all this but maybe someone else can benefit.
Short version of this is if you install every thing (including the motor) correctly and do periodic chain cleaning and lubrication maintenance & adjustment, even a little kit motor won't break a crappy kit chain.
Happy problem solving!
Rick C,
