Exploding chains

[Mighty_Max]

Ive assembled a wonderful motorized bike and managed to figure out pretty much everything to make it work, with a little help from the forum. It runs great and it goes pretty well too, however I've only put 11 miles (as stated by speedo) on it and I've killed two chains already. The first break was so catastrophic that it actually tore several of the links. This most recent one (10 minutes ago) only popped off the pin and might be repairable. This does bring up a good question though. Why does my chain keep breaking?

Note: The chain in question is the standard bike chain that runs from the pedals to the rear gear cluster. The first chain was the factory free one that came with the bike. After that broke I read up and figured out that i wasn't shifting properly, so now i only shift when off the power. The next chain was a cheap Bell one from walmart. That one lasted 3 miles.

Genesis 29" bike
7 speed rear gear assembly with Shimano Gripshift and derailleur
66cc Grubee Skyhawk engine
Sickbikeparts HD shiftkit
Sickbikeparts Expansion Chamber

 

[2door]

Do you have a 'shift kit' ?

Tom

 

[Mighty_Max]

Yes, as stated in the bottom of my post, its a Sickbikeparts HD shiftkit.

 

[isaac the kid]

definitely let off the power while shifting, do it like you would a manual car (use clutch).

It could be an alignment issue, if your chain is being torqued sideways it can certainly break it especially under load. Look at the derailleur while not shifting, it might be set too far in one direction and is rubbing against the chain constantly, also check your wheel alignment.

 

[Mighty_Max]

After i get a new chain, preferably not made by Bell, i will pay more attention to the derailleur. The wheal does seam to be in proper alignment.

 

[isaac the kid]

yea i wouldn't be buying a wall mart chain this time, i got a stainless steel chain with master link at my bike shop for only 10$, try to get something heavy duty cause they're usually not very expensive.

 

[The_Aleman]

You might need additional spacers between your crank sprockets. Obviously you have an alignment problem.

Another thing to watch out for is that derailleur bikes use thinner chain than single-speed bikes. Your front sprocket might need additional beveling on the teeth.
This will make it slightly less likely to break a chain, but if your alignment is bad enough, it's gonna break anyway.