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Old 09-27-12, 04:12 AM   #1
jhonan
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Brompton with 3000km - Sprocket worn?

The chain on my 1yr-old M6R broke yesterday so I decided to put on a new chain (same size and spec)

However, when I put the old chain next to the new one to count the links, I noticed the old one was longer - About 0.5cm over the length of the chain. I understand this is because the chain is worn (which is normal for 2-3k)

Anyway, I put the new chain on, and it started skipping - Could this indicate wear on the chainring or sprockets? - This has me confused as first I thought I'd get 10k out of the chainring/sprockets and also, they don't look worn to me - I'm looking for the 'shark-fin' pattern on the teeth, but can't see it.

In the end I fixed the old chain and put it back on.

Does anyone have any experience of chainring/sprocket wear on a brommie, and what it looks like?
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Old 09-27-12, 07:27 AM   #2
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Can't really say I can spot the worn sprockets with my eye but I changed my chain about the same time (after 3000km from new) and went through the whole skipping thing. Chances are good it is the rear sprockets that need replacing - mine did - good thing they are cheap and easy to change.
I don't like the stock Brompton chain - when I measured a new one, it had already stretched from ideal. My theory is that since they come "pre-stretched", they wear the sprockets down faster than a chain of the correct length.
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Old 09-27-12, 08:03 AM   #3
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This should be a silly question, as you said "same size and spec" but have you checked the width, even though you ordered the right one?

You probably know that Brompton "highly recommend" changing the sprockets with the chain. The sprockets are cheap (in Brompton terms anyway!). It's not blindlingly obvious to me either why that should be necessary or that the chain should come off, but there it is.

http://www.brompton.co.uk/extranet/d...f/ds-chain.pdf

http://brilliantbikes.co.uk/56-bromp...ts-and-spacers
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Old 09-27-12, 05:05 PM   #4
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This should be a silly question, as you said "same size and spec" but have you checked the width, even though you ordered the right one?
Yeah, I'm pretty sure - It's the Shimano HG40 chain;

Shimano HG-40 8-Speed Chains.
Item Specifications
Color Black
Weight 350g
Width 7.4mm
Links 116links
Number of Speeds 8-Speed
Chain Compatibility 3/32"
Defined Color Black

It lists it as 3/32", which is the width that Brompton recommend for a 6-speed. I'm not sure why the Amazon link says 7.4mm wide, elsewhere I've seen 7.3mm wide. But it was definitely shorter than the old chain I took off, for the same number of links.

I think I'll go with the suggestions and get a set of sprockets as well. Now, if I can just figure out how to get the powerlock link off this Shimano chain, it'd be great!
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Old 09-27-12, 05:38 PM   #5
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With the powerlink, push both ends of the chainlink together/towards each other, then twist. They should both come off in separate directions. Sometimes it gets a bit fiddly. Doesn't hurt to spray in a touch of liquid lube of some sort if it's sticky. Once it's apart, you'll see how to reverse the process - push both sides of the single link segment in and pull both ends apart.

Don
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Old 09-28-12, 12:49 AM   #6
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You can flip the 3 speed sprockets, but the BWR hub uses shimano's spline
the thick/thin spline combo can't be flipped..

Sachs 3 by 2 was better, both flat cogs could be flipped .. they used 3 spline fittings..
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Old 09-28-12, 04:32 AM   #7
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On my two speed Brompton I changed the chain after 1500 miles and it skipped on the highest geared cog. Changing the 12T cog for a new one fixed the problem.

The only way to prevent wear on the cog it is to make sure you use a chain wear indicator tool and change the chain before it stretches too much and wears the cog.

I now plan to maybe wipe my chain over a little more often to try and keep it cleaner and thus make it wear a little bit slower. There is a balance here and I certainly am not going to spend hours every few months cleaning dirty chains when they only cost around 10. Cogs/sprockets are also pretty cheap. That said any wear on the the larger main ring would be more costly.

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Old 09-28-12, 07:47 AM   #8
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Originally Posted by bargainguy View Post
With the powerlink, push both ends of the chainlink together/towards each other, then twist. They should both come off in separate directions. Sometimes it gets a bit fiddly. Doesn't hurt to spray in a touch of liquid lube of some sort if it's sticky. Once it's apart, you'll see how to reverse the process - push both sides of the single link segment in and pull both ends apart.Don
Unfortunately it wasn't the nice two-piece powerlink, it's something like this pic (but with the piece on the right as a complete loop). It locks into place, and is really hard to get off. Probably why they're not as common as the two-piece powerlink.
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Old 09-28-12, 07:51 AM   #9
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On my two speed Brompton I changed the chain after 1500 miles and it skipped on the highest geared cog. Changing the 12T cog for a new one fixed the problem.
I have a M6R (2 speed derailleur, 3-speed AWR hub) - I have a 16/13 sprocket setup. On closer inspection I noticed the teeth on the 13 cog are looking sharper than they should.

Also, I'm cycling on this cog 80% of the time. Combine that with a stretched chain, and I reckon I've got to replace these sprockets. But as you say, they're cheap enough.
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Old 09-28-12, 09:10 AM   #10
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3 piece connector shown is for a 1/8" type chain, most likely, ...
they have been around much longer than the 2 piece,
like KMC would package with their 5,6,7,8, speed 3/32" chain..

since the gear ratio is so much higher to turn the smaller wheel, more often
to have the same speed over the ground, as a bigger wheel .
it is logical to replace the 2 Cogs, at the same time as the chain..

With a 3 speed where the chain is not flexed sideways, a quick link
is a convenience more than a necessity, I am using a 1/2 link ..

so I open the chain in the same place .. and if issues arise , the 1/2 link is replaced.
the chain machine riveted pins remain un - disturbed.
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Old 09-28-12, 03:11 PM   #11
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With a 3 speed where the chain is not flexed sideways, a quick link
is a convenience more than a necessity, I am using a 1/2 link ..
Ah, that's what it's called, a quick-link. Yeah, I think you're only supposed to use them once - Don't see the point of that really, but anyway it's really hard to get off!
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Old 09-28-12, 04:03 PM   #12
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Never saw one of those before, thanks for the pic!

Now a different question - can you break the chain outside the quick link? I'm thinking if you don't push the pin all the way out, you might be able to ease it back in with a chain tool, but I'm in uncharted territory here.

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Old 09-29-12, 01:44 AM   #13
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That one is not the same, the Current quick link are 2 identical pieces
each with a pin and a keyhole.. those are easy to open, with Park's tool for the purpose..
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