3-speed Nexus hub

[wafflycat]

Picking of brains please.

MrWC has an acquaintance who has a Dawes something or other (about seven years old) with a 3-speed Nexus hub (chainguard over chain). Problems with selecting the top gear on a twist grip, plus there are times when the chain goes slack and derails either at 'sprocket end' or at chainwheel end. The LBS the guy is suing can't rectify the problem. Any ideas on what may offer a solution? Ta.

 

[llllllll]

I've got a Nexus hub on my chopper, unfortuantely I don't use it much so can't really comment on the shifting problem. However there's no derailers or chain devices involved in the drive-train, it's basically a single speed as far as the chain is concerned. So if the chain's coming off it can only be that it's either too slack (i.e chain is too long) or the chain line isn't straight.

Reading your post again, you say it 'goes slack', suggesting that it isn't always. That's a bit odd, the only way I can see that happening is if the chainring and or sprocket isn't perfectly round or perhaps one of them is bent?

 

[wafflycat]

I've got a Nexus hub on my chopper, unfortuantely I don't use it much so can't really comment on the shifting problem. However there's no derailers or chain devices involved in the drive-train, it's basically a single speed as far as the chain is concerned. So if the chain's coming off it can only be that it's either too slack (i.e chain is too long) or the chain line isn't straight.

Reading your post again, you say it 'goes slack', suggesting that it isn't always. That's a bit odd, the only way I can see that happening is if the chainring and or sprocket isn't perfectly round or perhaps one of them is bent?

Must resist temptation for smut... must resist.. must...

On a more serious note - thanks for the response. Next time MrWC gets to see his acquaintance, he's going to check the bike for things bent/wrong shape/out of alignment.

 

[llllllll]

Must resist temptation for smut... must resist.. must...

Must remember to proof read my posts

 

[jpembroke]

You need to first of all sort out the chain tension by pulling the wheel back in the dropouts. Does it have chain tensioners on the dropouts? Once you've done this you can sort out the gear adjustment. On a sturmey archer 3 speed you simple select 2nd gear and twiddle the barrel adjuster until notch/blue line/spiggot/thingy is level with the end of the axle when viewed through the spy hole in the hub nut (where the indicator gear chain enters the hub). I know that SRAM 3 speed is very similar to this set up so I'm sure that Nexus is fairly simple too. You will find more information on Shimano's website where you will be able to download technicals docs for the hub.

 

[wafflycat]

One of the things that tweeks my interest is that the person gets his bike maintained at a LBS, so one would have thought that they'd done the obvious like the chain length etc.

 

[jpembroke]

Some LBS's are just scared of 3 speed hubs. Personally, I'm rather fond of them.

 

[TheDoctor]

The only thing I can think of is if somethings's bent (fnarr...) - the chainring's the most likely suspect. Or possibly the axle's broked?
I have had hassles on a SS when the chainline was about a squillion miles out, but that shouldn't be the case with a commercial, not-been-messed-about-by enthusiastic-amateur bike.