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Old 04-06-14, 01:09 PM   #1
AGuinness
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Chain skipping with Sturmey Archer S-RF3 on a Brompton — Help!

Hi everyone,

First let me thank you all for helping in advance, I hope y'all can help me solve this little problem.

I recently swapped the rear hub on a Brompton, from the original single speed hub to a Sturmey Archer S-RF3. I think I have installed everything properly. However, the chain skips when I apply pressure to the pedals (when I ride it basically, or if I pedal it on the stand while lightly pressing the down the brake to simulate pressure). Without pressure on the pedals, it does not skip, although it moves a bit awkwardly if I pedal backwards. I think the problem may have arisen from the fact that we adapted a cassette cog to the hub, instead of using the original 18t cog that came with the hub. We used a thin 12t cassette cog, by dremeling the extra teeth. The chain tensioner looks fine, everything appears to be lined up properly. I am using a 1/8" chain, which is what I was using before with the single speed cassette hub. I tried using a 3/32" chain but the problem persists.

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Old 04-06-14, 01:46 PM   #2
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Originally Posted by AGuinness View Post
.... I think the problem may have arisen from the fact that we adapted a cassette cog to the hub, instead of using the original 18t cog that came with the hub. We used a thin 12t cassette cog, by dremeling the extra teeth.....
Extra teeth?????

One question, was it a NEW 12t cassette sprocket, or a used one? If it's a used one, you're probably suffering from the classic new chain/old sprocket issue that plagues derailleur bikes. This is expecilly likely with smaller sprockets ie 12t.

The other place to look is for any shoulders on either side of the sprocket which might be preventing the chain from settling fully down to the bottom of each tooth.

Other than that, I'd need more info, especially a close up of the sprocket with the chain wound around it.
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Old 04-06-14, 02:09 PM   #3
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The chain looks fine. I thought of that too. It wraps around the cog perfectly. Perhaps it is due to wear on the teeth of the cog, as you said, but I was using the same chain and same cog on the previous hub. Oh, and by extra teeth, I meant the inner teeth that guide the cog onto the cassette body. Maybe I need a larger cog, like a 14?
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Old 04-06-14, 02:14 PM   #4
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Could it be due to hub adjustment? I mean, is that possible? For the chain to skip under pressure, due to less/more tension than required? I'm also curious about the way I set up the cable, as it is usually set up on the "seatstay" rather than the chainstay, on most Bromptons I've seen. Could that also be a possible cause?

Also, sorry if this is a stupid question. I'm not too familiar with three speed hubs, or Bromptons. This is actually a friend's bike and I am trying to help adjusting it. I am a mechanic working in a small shop, but don't have much experience with this. Thanks everyone.

*I searched the forums, and found no info on this subject.

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Old 04-06-14, 02:28 PM   #5
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Old 04-06-14, 03:08 PM   #6
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Why do you not use the Brompton cable routing ?

which is up to a pulley block on the cgainstay and then back down,
the square tube in your next to last picture on the left above, is there to mount that,..

as I see it, your routing interferes with where the hook on the left side of the front wheel hooks over the right chainstay.

right where you clamped thaat housing stop..

BSR is the same as SRF3 AFAIK AW3 NIG..

remotely ... over the web, no I dont know why your chain skips.. I have had no issues with the BSR with 3 spline cogs ,
Mine is a 15t 3/32" thick stock 13t was 1/8"
actually '12t' because I got one from the Sachs 3 by 2 6 speed there they skipped every 5th tooth so 3 are shorter, to help the shifting ..

are you using a cassette Derailleur cog or are you using the Brompton or a BMX 9 spline cog?
and if not is that derailleur cog on backwards?

Last edited by fietsbob; 04-06-14 at 03:11 PM.
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Old 04-07-14, 10:09 AM   #7
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The cog looks like it came off a 9 speed cassette, and I placed it correctly. I will try to change the cable routing to the seatstay, but I don't have the cable pulley assembly that mounts to the braze-on. I hadn't noticed that my routing would interfere when folding the bike.

So is it possible for the chain to skip under pressure due to maladjusted gears? I'd kind of like to narrow down the possible causes.
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