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Discussion Starter · #1 ·
Hello everyone...hoping for some advice here :)

I serviced my old Alfine a couple of months ago, I was stunned to find it perfectly clean inside despite being used on a mountain bike that is not afraid of horrendously gritty British riding and fording through rivers. I re-greased sparingly using Land Rover swivel grease as per recommendations elsewear, did not bother to dip the hub as I saw little point removing the lube inside the hub when it was so clean. I replaced the worn Alfine 20t with a new Nexus 20t with the chainguard. I have always run the cogs flipped to correct the chainline.

It has been running fine since the service including some tough climbing, the only issue was a tiny bit of drag so it would freewheel the cranks if you took your feet off. In an effort to diagnose this I backed off the cones slightly which did not resolve it, so I flipped the cog back to standard, thinking perhaps the chain guard was fouling the hub.

On my next ride the hub lost drive within 10 metres of gentle pedalling, took the shifter mechanism off and found the wire snap ring had come out. I flipped the cog back to how I normally run it (backward) and put the wire ring back, Remounted the bike and it immediately happened again. This time I could not get the wire retainer out, we messed around and mangled the retainer and gave up when I realised the cog seemed to have moved forwards, making it impossible to get the retainer out without snapping it.

Once back at home I realised the cog had popped forward off the splines and rotated. I used a chain whip tied to the spokes to hold the sprocket, and a drift and hammer in the hub spline indents to tap it back to the correct position, at which point the retainer dropped out and the cog could be removed.

I'm not sure whats going on, it seems related to the fact the wire snap ring is was past its best (its always been a little distorted since I got the hub second hand) so will definitely need a new one, but also it appears that the gap to get the retaining ring installed is smaller when the Nexus cog is flipped, and its hard to get the ring installed. I suspect its not properly seated in the groove. The alfine cog seems OK both ways. Should I break off the plastic chainguard, it doesn't seem to be prevented the cog from sitting properly? Or perhaps I've not reassembled the hub properly after servicing it?

Gear Bicycle drivetrain part Bicycle part Machine Crankset
 

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The chainguard is not meant to be run in that configuration, yes, but more importantly, that is not the proper snap-ring for the hub. The Alfine (and higher-end Nexus) hubs use a square snap-ring. You can find the part number if you pull up your hub at www.si.shimano.com .

You almost need snap-ring pliers to install them, by the way--they're very tight.
 

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Discussion Starter · #3 ·
Hello! I have to admit I doubted you when you said the snap ring was wrong, but I looked it up as suggested and was stunned to find you are correct and it should be a square profile and the ends meet, the wire clip I have at the moment has a small gap and comes off very easily! After shopping around I have managed to find one without absurd postage costs, £3.81 for the snap ring, and £11.49 for a complete cassette joint unit as I could not find anyone selling the broken bit.

The different snap ring gives me hope that I'll be able to fix this as where the cog has slipped, it has marred the 3 splines a tiny bit so the cog almost wants to walk off the splines when rotated. Once the bits arrive I'll consider cutting off the plastic guard but I might try it the otherway round first. The hub is an S501.

P.S the link is si.shimano.com , doesn't work with www prefix!
 

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In our world of auto-complete-ing web addresses, I sometimes forget that "www" isn't added to everything.

Just as an FYI, it is recommended to install the snap-ring, then use a narrow punch to (co-axially with the axle) make sure it is seated all around.

I would personally just replace the sprocket; once the lugs begin to strip, it's effectively dead, and not to be trusted as a daily rider. You don't need to use an Alfine sprocket...anything from a cheap-as-chips coaster brake sprocket, to a Nexus sprocket (if you want to keep it Shimano) will work. The key is that it is a standard 3-lug sprocket, and it fits with no side-to-side play with the snap-ring engaged. Without the chainguide, you need to make sure that the chainline of the sprocket, crank, and tensioner (if present) match, otherwise the chain can derail and take out the cassette joint unit.

Personally, I used a 1/8" Sturmey Archer sprocket, not just for the size/wear resistance, but because it was symmetrical, and could be flipped around when it was worn out in one direction.
 

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Discussion Starter · #5 ·
Hello again. Well I have the new parts, but something is still not right! I've removed the chain guard from the new cog, but whether I use the old or new cog and flipped whichever way, the new snap ring will only just squeeze under the lowest profile sections of the cog, where the raised indentations are there is not enough clearance, I've not even tried to drift it in as I don't think it will go.

I've attached a photo which shows my order of installation, I suspect the cog is not sitting deep enough in the splines.

As a side note, when I serviced the hub I only removed/adjusted the non-drive side cones as I didn't have an 18mm cone spanner for the driveside. After reassembly, I back off the cones slightly to see if it had an effect on the freewheel drag. However I just put a spanner on each side and 'I think' the driveside cone and locknut backed off slightly i.e. I adjusted the driveside cones a half or full turn, could that affect clearance? I have just ground a cone spanner out to 18mm but it seems its either seized or clipped in place to avoid adjustment as it doesn't want to move!

I'm out for a bit but will check back later to see if anyone has any golden nuggets of info for me...thanks!

Bicycle part Rim Bicycle accessory Bicycle tire Spoke
 

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Discussion Starter · #6 ·
I've taken the hub apart again but cannot see anything wrong. Messed around with it for a while and whilst removing and replacing part 14 I noticed there was a metal ring/spacer that fits snugly inside 14, I originally though it was part of the hub itself. I removed it and now the snap ring fits nicely over the hub, looks solved.

This part isn't on the exploded diagram for my SG-S501 hub, I've not had time to look at the other diagrams but I wonder if its been reassembled by someone familiar with an older variant, which would explain why the snap ring was wrong also?

Dust seal 33 was also missing, I got a new one with the shifter mechanism. The locking part 35 seems looser than before but perhaps this is just because the new unit is clean...will go easy on it to begin with.
 

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A few thoughts in no particular order (the previous post was eaten by the system)

-The RH cone, despite the flats/locknuts, is not actually threaded on. It is a press fit; there is a tool to set the cone on with proper depth, after which the locknut is turned down/tightened.

-The wheel bearing adjustment for the Alfine series (and all modern Shimano IGHs, really) is accomplished from the LH side. It is best accomplished by clamping the RH flats on the axle in a vise, and adjusting the play until knocking/movement is no longer felt at the rim). Wheel bearings on IGHs do not particularly contribute to lazy coasting--that is the almost exclusive domain of the planetary gears rotating. When two planetaries are rotating at the same time, apparent coasting drag is high, but when one is locked in place, apparent drag is low.

-The RH cone being out of place should not directly effect the sprocket mounting, but if it were out of place, and the whole assembly shifted left in the hub, the dust covers/seals could prevent it from mounting properly. In an extreme case, the cone being out of place could effect driving of the hub, since it helps to preload the clutch spring.

You need several special drifts to remove/install the cone/seals in the hub. The TL-8S11, TL-AF20, TL-AF30, and TL-AF10.
 
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