Modification Fail

[Morgann]

Trying to fit a smaller (Shimano CS-S500)rear sprocket to my ProConnect. The new sprocket has a plastic chain guard and, for some reason the chain keeps fouling it and lifting off the sprocket.

Its as if the new sprocket is less deeply dished than the old one and the chain tensioner is too far outboard to cope. Anyone seen this before or, know how to adjust the tensioner to angle in a bit?

I asked 50Cycles but got "Sorry, best ask the techies tomorrow." which is fair but the bike's in bits... and would have asked this in Technical but I don't have posting rights in there it would seem.

Any ideas?

 

[Blew it]

This may be of help.

Click the link below, enlarge the pdf file to 300% using the + button, check your re-assembly of your new sprocket is correct.

SG-S500 EXPLODED VIEW

Next, click the link below and expand the file to 300%. At the top of the file you will see a title 'WHEN USING THE CHAIN TENSIONER' This may give a clue as to why the wheel is too far over to the non-drive side. Make sure the anti-turn washer is properly located in the frame drop-out. Especially, the one on the non-drive side.


CT-S500 CHAIN TENSIONER

Hope this is of some help for you.
Regards
Bob

 

[Morgann]

Thanks mate. Yeah, thats the instruction sheet that came with the sprocket. I put the old one back on and did everything back up and it all worked perfectly; non turn washers on the correct sides, check. Everything properly seated, check. Spin round the block (mind the ice) yup, like a Swiss watch.

Put the Shimano back on and we're back to the chain chattering and jerking and trying to climb off the sprocket.

S** it. I'll take it to the lbs. There's a decent one in Ramsbottom; helpful enthusiasts.

Thanks for trying tho.

 

[Blew it]

No prob, hope you get it sorted.

 

[flecc]

If you've done quite a mileage on the chain, it will tend to climb off a new sprocket due to the longer link wear length, so that won't help matters.

 

[Morgann]

Sorry Flecc it's not that. The chain has less than 300 on it as does the bike. I had the sprocket mounted as per the Shimano instructions, with the plastic chain guard on the outside. This meant that the chain was riding up onto the guard before it reached the sprocket which of course lifted it away from the teeth.

50Cycles showed me a photo which showed it fitted the other way round with the guard on the inside so I tried to fit it that way only to find that the groove that the circlip drops into was now masked.

I removed the alloy dust cap underneath the sprocket which allowed me to push the sprocket further down and get the circlip fitted and it all works now but it feels like a bit of a bodge frankly.

If you look at Blewits' link for the SG-S500 above, you'll see that the the guard is clearly supposed to be on the outside so I don't know what's gone wrong there.

 

[flecc]

That certainly is odd. There's shades in this of how the Shimano plastic spoke guard disc that went behind multi-sprocket freewheels could bind or buckle slightly and impede the freewheeling action, account here.

 

[Blew it]

Aha!, I've just had a quick look at my Kalkhoff Sahel, my plastic guard is also fitted inboard of the sprocket.

This can just be seen in the photo below.

 

[Morgann]

Got a good mind to knock the verdamnt guard plate off and install the sprocket the right way round! It's not supposed to be this hard. And... i've got a set of Big Apples coming tomorrow to be shoehorned onto the bike!!

Oh well at least it's something to do while we wait for the weather to change.

Mutters darkly​

(Should have bought Sram)

 

[JamesC]

There is a useful drawing of the Alfine Hub with Tensioner on the Hubstripping website here.

I think that the Alfine uses a plastic chain guide both inside and outside the sprocket. The inside one clips over the hub, but the outer one is part and parcel of the Alfine sprocket.

Note that there is a shim to align the tensioner with the sprocket, and that any dishing on the sprocket looks as though it is inwards, moving the chainline towards the wheel.

From memory, I think that the Alfine sprocket with chainguard is only available as 18 or 20 teeth.

The Nexus hubs are more or less the same dimensionally, except that the sprockets did not use a chain guide.

Nexus sprockets are dished, and when fitted to the earlier ProConnects/Agattus etc, they are fitted with the dish taking the chainline away from the wheel. This gives better alignment with the Panasonic Chainwheel.

Blew It
I wonder whether the Sahel is fitted with the Alfine hub complete with inner chainguard, plus a Nexus sprocket moving the chainline away from the wheel.

I wonder whether a thicker shim/spacer is used between the tensioner and the frame to align the tension jockey wheels with the sprocket.

The range of Nexus sprockets goes from 16 T to 23 T, but the larger sprockets may clash with an Alfine tensioner ?? There may also be a difference in the width of the teeth; many Nexus hubs run with 1/8" chain.

Do the Alfine hubs/sprockets run with 3/32" chain ?

James

 

[Blew it]

James,

I'm not really sure. Originally my Sahel was fitted with an 18T sprocket ( 26" wheels ). When changing to a 16T, I just laid all the components out in sequence on the bench as you do. When reassembling, everything was refitted in reverse order.

I suspect the plastic ring serves two purposes, acting as a muck flicker and also protecting the cassette joint if the chain de-rails. Obviously it can't perform this latter function when fitted inboard of the sprocket.

Somewhere in the back of my mind I recall that both the Panasonic chainwheel and Alfine/Nexus sprockets will accept both 1/8" and 3/32" chains. Perhaps a way of standardising for either geared hub or derailleur.

Back in July last year, there was a thread to which both yourself and NRG contributed regarding these matters. CLICK HERE

Anyway, must fly. One of the machines I sold on last year got T-boned in Swindon the other day, major re-build required

 

[JamesC]

Further to my earlier post:

If the Alfine tensioner is the CT-S500 with 2 pulley wheels, the parts list shows 2 shims (1mm thick and/or 2mm thick) that can be fitted between the frame and the tensioner.

These shims are available from Petra Cycles here.

I am guessing that you would be right to use the new Alfine sprocket that you are working with, leaving off the outer plastic shield. Fit the dished sprocket with the chainline away from the wheel.

You may need additional spacers to achieve perfect alignment between the tensioner pulleys and the sprocket.

Obviously, perfect alignment becomes more important when the width of the chain is a close fit with the sprocket. I mentioned above that early bikes were fitted with wide chain (1/8") that was a generous fit on the sprocket teeth.

James

 

[Morgann]

I too was coming to the conclusion that the plastic guard plate was surplus to requirements. Just got an email from 50Cycles giving removal as an option so, shall do that and turn the sprocket the right way round and refit the dust cover.

At this rate I'll end up having to buy an actual pair of circlip pliers; must be the 8th or 9th time I've had the thing apart

Thanks for everyones help and the links. That was a lot of head scratching to be caused by a superfluous bit of plastic.

 

[kitchenman]

That was a lot of head scratching to be caused by a superfluous bit of plastic.

don't throw it away it may come in useful. I had a similar issue with a chain guard: