Problems with Nexus

[desperadono]

Hi
I have just bought a second hand city type bike with a 4 speed nexus gear system. In general terms its in very good condition but has one problem that i am finding hard to solve, the front chainring was noisy when riding and jumped off sometimes on checking I found that the chain very slightly rides to one side on the chainring as if its out of line. There are no adjustment or spacers I can see to get the chain running true with the rear gear and. the chainring and gear don't seem worn and as it's the originals It can't be compatible. The only thing I can see is that the chain seems rather wide compared to the Gear/chain ring which are rather thin, could this be the problem? Any ideas?

[Alex Ramon]

You should be able to see which way the chain is off by looking down the chain from the rear. If it looks like the chainring needs to be moved out more you may be able to correct it by changing the bottom bracket spindle length.
You likely have a single-speed chain installed, which are ok to use with a Nexus, and are generally wider than traditional multi-speed gear chains.

[desperadono]

Thanks Alex

[DaveM]

It may be hard to tell, but unless someone changed something on the bike, it seems unlikely your chain line would have shifted. Check it by eye. But it also could be that the chain is "stretched" or just too loose.
The chain should be tight enough that it can't move up or down more than an inch halfway between the front chainring and rear wheel.
To check chain stretch, look at how it fits into the teeth on the chainring. If it does not drop completely into the bowl shape of each tooth, it is probably worn out. Get a replacement.