I have a 750W Bafang mid train motor. The teeth on the chain ring are being destroyed after only 80km (50 miles) riding. The chain just comes off now if I try to ride it, because the teeth are so bent and broken.

I took it back to the shop, and was accused of dropping it... I don't know what sort of bad experiences he's had with people but considering I just paid £1750 you'd think he would actually think about it first, especially considering the alternating nature of teeth being broken.

The chainring came with the motor, so it's hard to understand if it's an issue with a weak chainring, unless it was just an unusually bad batch. I'm wondering if the gears were possibly set wrong or the chainring.

Any opinions/ideas are welcome.