Hub Gear problem - not electric bike specific

The Maestro

Esteemed Pedelecer
May 15, 2008
296
0
Hi,

Having problems with the Nexus inter-8 on my converted ebike. Does anyone have any experience on these hubs?

The set-up is a vertical drop-out bike with the shimano fitting kit and none-turn washers for vertical dropouts. 1/8 nexus chain, 4Jeri chain tensioner, standard chainwheel (which is apparently ok).

What happens is that the gears slip badly in every gear with even marginal pedalling force to the point that its unusable. Watching the chain tensioner when this happens it moves upwards against the string tension and then it flicks back down when the gear slips. At first I thought it was the tensioner but I've tried it without the tensioner fitted and got the same slipping problem.

The cable is correctly tensioned with the markers aligned. THe chain path is not 100% straight but not bad.
 

JamesC

Esteemed Pedelecer
Sep 1, 2007
435
5
Peterborough, UK
Hi,

Having problems with the Nexus inter-8 on my converted ebike. Does anyone have any experience on these hubs?

The set-up is a vertical drop-out bike with the shimano fitting kit and none-turn washers for vertical dropouts. 1/8 nexus chain, 4Jeri chain tensioner, standard chainwheel (which is apparently ok).

What happens is that the gears slip badly in every gear with even marginal pedalling force to the point that its unusable. Watching the chain tensioner when this happens it moves upwards against the string tension and then it flicks back down when the gear slips. At first I thought it was the tensioner but I've tried it without the tensioner fitted and got the same slipping problem.

The cable is correctly tensioned with the markers aligned. THe chain path is not 100% straight but not bad.
I am wondering why there would be movement on the chain tensioner if the slippage is occurring inside the hub.

It sounds too obvious, but that movement on the chain tensioner sounds almost as though the chain is slipping over the teeth on the rear sprocket.

Is that possible ?

Most models in the Nexus 8 hub range can accept a smaller rear sprocket down to the smallest at 16 teeth. However, at this small diameter, the dished sprocket has to be fitted such that the dish takes the chainline away from the hub.

If a 16 tooth is fitted the other way round, the chain rides against the plastic shield of the hub and is lifted off the teeth of the sprocket. You would see movement in the chain tensioner if this sort of thing is happening.

It would be helpful to know:
1. How many teeth on the hub sprocket ?
2. Is it a dished sprocket ?
3. Which model number is shown on the Nexus 8 hub ?

James
 

The Maestro

Esteemed Pedelecer
May 15, 2008
296
0
I am wondering why there would be movement on the chain tensioner if the slippage is occurring inside the hub.

It sounds too obvious, but that movement on the chain tensioner sounds almost as though the chain is slipping over the teeth on the rear sprocket.

Is that possible ?

Most models in the Nexus 8 hub range can accept a smaller rear sprocket down to the smallest at 16 teeth. However, at this small diameter, the dished sprocket has to be fitted such that the dish takes the chainline away from the hub.

If a 16 tooth is fitted the other way round, the chain rides against the plastic shield of the hub and is lifted off the teeth of the sprocket. You would see movement in the chain tensioner if this sort of thing is happening.

It would be helpful to know:
1. How many teeth on the hub sprocket ?
2. Is it a dished sprocket ?
3. Which model number is shown on the Nexus 8 hub ?

James
Thanks James you sound very knowledable! The rear sprocket is 19T Nexus type. It is dished placing the chainline nearer the hub (I didn't fit this one, if I had I would have put it on the other way :) ). It doesn't seem to be hitting any of the plastic on the hub gear. THere is very smooth motion if I lift the rear wheel in the air and turn the pedals.

I doubt its slipping over the rear teeth. Its a brand new Nexus specific chain and the rear sprocket doesn't look worn. Of course the chain tensioner means that chain doesn't wrap around the bottom teeth of the sprocket as they would without one.

To me the chain tensioner moving up and then springing down says that the chain tension is increasing at the bottom run of the chain pushing it up, and then all of a sudden there is a loudish noise, a slip and the chain tensioner springs back down.

Edit: Part no. is SG-8R25
 
Last edited:

flecc

Member
Oct 25, 2006
52,761
30,348
I agree with James that this sounds like the chain is jumping the sprocket teeth, even with the 19 tooth sprocket. The tensioner behaviour and the fact that it happens on all gears in the same way all points to that.

I can only suggest stronger spring tension or a reversed tensioner action that wraps the chain further around the sprocket rather than decreasing the wrapping.
.
 

The Maestro

Esteemed Pedelecer
May 15, 2008
296
0
I agree with James that this sounds like the chain is jumping the sprocket teeth, even with the 19 tooth sprocket. The tensioner behaviour and the fact that it happens on all gears in the same way all points to that.

I can only suggest stronger spring tension or a reversed tensioner action that wraps the chain further around the sprocket rather than decreasing the wrapping.
.
I've tried it without a tensioner. I broke the chain to the correct length and was lucky that it was a nice fit.

Could it be anything to do with the front chain wheel/ring? This was the original one from my derailleur setup. I thought that I wouldn't be able to use it but all the single speed conversion guides I've seen say that you can use the original. I did have slipping problems on my derailleur setup too but less severe and spraying everything with chain wax sorted it. Change front chain ring maybe ?!?

I like the idea of a push up tensioner and have seen a few but wasn't sure if they were suitable for my bike. Mine just screws into the rear derailleur hanger hole.
 

flecc

Member
Oct 25, 2006
52,761
30,348
I doubt it could be the front ring since with the chain the correct length as you now broke it to, it wouldn't be able to climb above all the teeth of the front ring. It would need inches of slack for that.

It's baffling that you have the slippage in every gear though, something that doesn't normally happen with these multi-gear hubs.
.
 

The Maestro

Esteemed Pedelecer
May 15, 2008
296
0
I doubt it could be the front ring since with the chain the correct length as you now broke it to, it wouldn't be able to climb above all the teeth of the front ring. It would need inches of slack for that.

It's baffling that you have the slippage in every gear though, something that doesn't normally happen with these multi-gear hubs.
.
I bought it off ebay. Looked in good condition and the seller sold a lot of bike bits and had good feedback but someone obviously took it off a bike for some reason. Came with Marthon plus tyres half worn. Bad hub? I think Its bust.

Maybe I'll take it lbs and tell em no win no fee :) Still this is annoying my I only have petrol transport available now :(
 

JamesC

Esteemed Pedelecer
Sep 1, 2007
435
5
Peterborough, UK
The rear sprocket is 19T Nexus type. It is dished placing the chainline nearer the hub (I didn't fit this one, if I had I would have put it on the other way :) ). It doesn't seem to be hitting any of the plastic on the hub gear. THere is very smooth motion if I lift the rear wheel in the air and turn the pedals.

I doubt its slipping over the rear teeth. Its a brand new Nexus specific chain and the rear sprocket doesn't look worn. Of course the chain tensioner means that chain doesn't wrap around the bottom teeth of the sprocket as they would without one.

To me the chain tensioner moving up and then springing down says that the chain tension is increasing at the bottom run of the chain pushing it up, and then all of a sudden there is a loudish noise, a slip and the chain tensioner springs back down.

Edit: Part no. is SG-8R25
The 19T sprocket can be used either way round - I have used it both ways.
The SG-8R25 is a good vintage being the one of the best "red band" hubs.

Your comment above about there being no chain wrap around the bottom of the sprocket due to the position of the tensioner does not sound good. I would agree with Flecc's suggestion to use an upward tensioner to put the load around half the teeth rather than only a quarter of the teeth.

BUT you say the problem also happens with a fixed chain, and it runs sweetly in all gears with no load when the back wheel is off the ground.

If the problem is inside, and affecting all gears, it might suggest the free-wheel pawls are not engaging properly. The only time I have heard of something similar is when the wrong "internal assembly" (which contains the pawls) has been fitted into the wrong external casing (which contains the mating grooves).

Is this a new, complete hub or one that might have been rebuilt with a new internal assembly ?


You still need a good chain wrap around the sprocket !

James
 

The Maestro

Esteemed Pedelecer
May 15, 2008
296
0
The 19T sprocket can be used either way round - I have used it both ways.
The SG-8R25 is a good vintage being the one of the best "red band" hubs.

Your comment above about there being no chain wrap around the bottom of the sprocket due to the position of the tensioner does not sound good. I would agree with Flecc's suggestion to use an upward tensioner to put the load around half the teeth rather than only a quarter of the teeth.

BUT you say the problem also happens with a fixed chain, and it runs sweetly in all gears with no load when the back wheel is off the ground.

If the problem is inside, and affecting all gears, it might suggest the free-wheel pawls are not engaging properly. The only time I have heard of something similar is when the wrong "internal assembly" (which contains the pawls) has been fitted into the wrong external casing (which contains the mating grooves).

Is this a new, complete hub or one that might have been rebuilt with a new internal assembly ?


You still need a good chain wrap around the sprocket !

James
Anything could have been done to it in its life, I bought second hand. It doesnlt look tampered with though and it freewheels superbly. Maybe I'll look into a push up tensioner. The chain was a little slack when I broke it to work without a tensioner but not something I'd usually concern myself about. I don't have much experience with these hubs - do they need a really tight fit and complete wrapping?
 

JamesC

Esteemed Pedelecer
Sep 1, 2007
435
5
Peterborough, UK
Anything could have been done to it in its life, I bought second hand. It doesnlt look tampered with though and it freewheels superbly. Maybe I'll look into a push up tensioner. The chain was a little slack when I broke it to work without a tensioner but not something I'd usually concern myself about. I don't have much experience with these hubs - do they need a really tight fit and complete wrapping?
I can't judge exactly when it would slip, but sharing the load around as many teeth as possible is good.

Just rechecking, did you say that you are using the Nexus 1/8 inch wide chain that is correct for the Nexus hubgear sprocket ? Narrower derailleur chain could climb up the teeth and jump when the chain tension rises.

James
 

The Maestro

Esteemed Pedelecer
May 15, 2008
296
0
I can't judge exactly when it would slip, but sharing the load around as many teeth as possible is good.

Just rechecking, did you say that you are using the Nexus 1/8 inch wide chain that is correct for the Nexus hubgear sprocket ? Narrower derailleur chain could climb up the teeth and jump when the chain tension rises.

James
Hi James, I originally used a normal derailleur chain (school boy error) and got the slipping problem so the latest development is that I got the specific nexus 1/8 chain, fitted it today and still have the same problem.
 

The Maestro

Esteemed Pedelecer
May 15, 2008
296
0
Well I found this thread on a single speed forum slipping chain....possibly end of my singlespeed experiment... « Singletrackworld

Most people are saying swap to a push up tensioner. Hopefully I can just put the spring in the other way around to make it push up. Another person said that a standard front chainring will try and slip the chain off if the chain line is off so it might be worth changing that to a bmx one somehow. I hope I don't have to go inside and change the mechanism. Anyway, I have a few things to go at now :)