Giant La Free Twist Comfort problems

The chain keeps coming off the rear sprocket, Sram 7 speed hub. I have replaced the chain, the sprocket and the chain tension wheel. I replaced the sprocket with 19T I wondered if it should be 18T? and would this effect it at all? Can anybody tell me how many teeth the rear Sram sprocket should be please for this model?

I'm not certain on the sprocket tooth number for the 7 speed comfort Roy, but a one tooth difference would not cause the chain to jump off. Regarding that jumping problem:

 

If you haven't changed the 14 tooth motor sprocket it will be worn and not matching the new chain, so the jumping that causes can "snake" the chain and cause it to jump off the rear sprocket.

 

Another common cause is the wrong chain type, 3/32" derailleur instead of the 1/8" chain it should be.

 

A tight link rivet that doesn't allow two chain links to rotate freely is another possible cause.

 

Let me know if any of those could be the answer.

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Could also be chain alignment.

From behind the bike with the motor cover off check if the chain is in direct line with all off the sprockets.

Rotate the chain to see if there's no bent in it.

Is the rear sprocket in correct position, bent inside teeth outside or have a false flat sprocket.

This in addition to flecc's good remarks.

 

Sorry for my english

Thank you very much for your help, have been going crazy. I ended up taking the bike to the shop where it was purchased for more advice. They told me I had fitted the rear sprocket wrong and it should flange inwards towards the wheel not outwards as like the Sturmey Archer. So they have changed it but, now seem to have a terrible problem with the chain case rubbing. This was not such a problem before. Very strange

That's odd, the SRAM sprockets are dished the most, 3 mm, Shimano's same fitting dished by 2.5 mm.

 

Sounds like you need a flat sprocket, but SRAM only make the flat ones as 17 teeth. If yours has 17 teeth you can get a flat one on this link.

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