IMO
This, is among the problems with the HT/chinagirl design.
The chain drive sprocket is too small ans packed in too tight a casting so a larger sprocket may not be installed.
What is occurring here is, when under power, the chain is drawn very sharply by the sprocket teeth contributing to accelerated wear.
Additionally, the chain is physically thrown away from the sprocket, when under load, and the small enclosure of the casing is frequently hammered by the chain, sometimes causing a lockup.
In the occasion of decelerating, forces from the chain against that small sprocket are also generated, especially when bump starting the motor!
Once again, IMO, the design would be much improved with a larger diameter 13t sprocket, yet there is no easy fix for this without serious modification of the case.
...Somewhere I read an opinion that the drive sprocket should always be a primary number to avoid harmonics and premature chain wear...
I'm not sure how that would work to advantage when the rear sprocket is a 4:1 ratio of the primary sprocket...
IMO
Most chain probs are caused by a rag joint NOT suitably fixed in a concentric position, running in an oval shape, making the chain tight, then loose, in each revolution.
This will cause undue strain on the tensioner and increased likelihood of a hangup at the drive sprocket.
Also, too long of a chain, (by a link or two), will require the chain tensioner being positioned farther back, or higher up in it's mount, putting a sharp angle in the chain.
This configuration will put a lot of torque on the tensioner bracket, forcing it inwards on a collision path with the spokes.
Hope this is helpful for consideration...
Best
rc
