Removing brompton sprocket

Tim Woodall said:

I need to replace the sprocket on my Brompton. I have a
Sachs 3 speed hub.

Quoted message said:

How do I remove it?

The sprocket is held on by a circlip. Prise the circlip off with a small
screwdriver, and the sprocket simply slides off.

There may (or may not) be a plastic dust cover over the circlip. Pull,
twist, or prise as necessary to remove it.

Quoted message said:

(I've got a replacement sprocket but I'm not certain it's the
correct item. I think it's the 13 tooth sprocket for a 6 speed
Brompton. Maybe it will fit anyway?)

The 6-speed sprocket is narrower than the 3-speed model. It will work as a
replacement, but you'll need a spacer to take up the extra space on the hub
driver.

Quoted message said:

I do have a chain whip and the replacement sprocket "fits"
the lockring so maybe I can undo it with that?

I think you've mistaken the splined end of the driver for a lockring. You
don't need the chainwhip.

James Thomson

On Tue, 22 Feb 2005 01:56:28 +0100,

James Thomson said:

I think you've mistaken the splined end of the driver for a lockring. You
don't need the chainwhip.

This was the problem. Thankyou. Amazing how much better you can see in
daylight too :-)

Thankyou for your help. I now haven't got to suffer the tube for a
second day :-)

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t,"
and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/

Tim Woodall said:

This was the problem. Thankyou. Amazing how much better you can
see in daylight too :-)

Isn't it? That's why I'm always amazed by tales of blind mechanics such
as Guy's tandem stoker, Bob. If they performed ony a few set operations
on a limited number of components that would be impressive enough, but
the fine details of bikes are highly varied. If a clued-up sighted
person has trouble distinguishing the end of a splined shaft from a
lockring, how on earth does a blind person manage it, even if he or she
is a mechanical genius, especially the first time they encounter a new
variant of something? Maybe this smooth thing is a plastic cover and
maybe there's a circlip under it and maybe I can prise this bit off, or
does it need to be unscrewed with a special tool, or is it just part of
the sprocket? How about building a wheel without looking at it, or even
adjusting an indexed derailleur? And not simply doing these tasks but
doing them to an exacting standard. I can't imagine being able to do
any of it myself.

--
Dave...

On Tue, 22 Feb 2005 01:56:28 +0100,

James Thomson said:

The 6-speed sprocket is narrower than the 3-speed model. It will work as a
replacement, but you'll need a spacer to take up the extra space on the hub
driver.

Interestingly, the sprocket I got yesterday had a shoulder so it was 3mm
thick on the hub but only 2.1mm thick at the teeth so the spacer that
was there for the old cog is still ok for the new cog.

I went into the shop again today to see if I could get another one so I
have a spare and they didn't have any more like this. I've tried
ordering one :-)

I prefer the thinner cog because now I can use a "normal" chain.

I'm amazed how quickly and drastically my chain had "stretched" - Ok,
I'm not very good at checking regularly, but it's gained 1/2" in each
12" over the last 2000 miles or so! - It had gained so much length that
on Friday the chain started skipping at the front if I pedalled hard.
It has never skipped at all until Friday. Then it was skipping every
time I pulled away unless I was very gentle. I could also see that the
chain literally didn't fit around the front cog.

I'm not certain that the rear cog was actually ruined. Putting it next
to the new cog there is some wear but the teeth are not hooked. At at
5GBP for a new cog it wasn't worth bothering trying it. (In addition I
would have needed a new chain because my spare chain would be too narrow
for the 3mm standard cog but I didn't know that at the time :-)

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t,"
and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/