Brompton: Weird happenings with new chain

slowestrider

I've just bought a new to me 2019 M3 Brompton.
It was used for commuting between terminus station to station commuting, so I'd guesstimate 1500-2000 miles. Previous owner didn't do much in terms of general maintenance and the bike suffers from minor rust of some of the fasteners etc.

The chain was clean, but bone dry and rusty. There are plenty of hills where I live and I didn't like the standard gearing of 50T, 13T (3 speed). I should've done a little more research and gone for a dual chainring, but I bought the Brompton 44T.

This morning I installed the new chainring to lower the gearing and fitted a new 3/32 chain, made by KMC the Z7 version. The new chain is much more flexible and smooth. Also found it a lot quieter on the stand.

I inspected the sprocket and it didn't look worn to me. However, when applying torque going uphill I found that it slipped. Same symptoms as a knackered cassette. Adjusting the gears didn't make any difference, I inspected the hub area, tensioner etc but it all looked good. Had a go at adjusting the gear changing chain. Still the same problem.

I put the old chain back on after removing a couple of links and no problem.

What's the problem? Worn sprocket? New chain dodgy?

veronese68

Sounds like a worn sprocket

slowestrider

So now I either :
a) keep using the old chain and sprocket - It shouldn't wear out anything else out in the drivetrain? My new 44T chainring?
b) buy a new sprocket to go with the new chain

My bike use a 3 gear Sturmey Archer hub thingy.
I've read that they don't need much in the way of maintenance, not like a cassette and derailleurs.
I presume they're packed with grease and don't require regular lubing?

slowestrider

Ok, I'll get a new sprocket. I prefer the new chain, much nicer. Looks like it needs a special tool to remove the old one. I've got one of those chain with a hook and handle, but I don't think it'll work with this.

wilberforce

Is it not just held on with a circlip? https://www.youtube.com/watch?v=cJDPpZlkdvs

ugo.santalucia

All you need is a screwdriver to remove the circlip... putting it back can be a bit of fun, until you master the technique

However, those sprockets should last a lifetime and I suspect your chain is not compatible with them... why didn't you buy the Brompton chain, is not that expensive...

slowestrider

Ah, yes - I forgot about youtube.
That explains it very nicely.
As for the chain, I used Amazon as they offered Saturday morning delivery.

I'll change the sprocket, £12.50 (16USD) from Brompton and start with a new chain, chainring and sprocket.

Thanks for your help.

ugo.santalucia

I always had troubles mixing multi speed chains with single cogs, even if the cogs were meant for multi speed chains...

slowestrider

Whilst look for a new sprocket, I came across a couple of sellers on Ebay with as new 6 gear rear wheels, from people exchanging them for the all-black edition wheels for an ok price, so now I've ordered all the bits to turn my M3L to a M6L. Talk about scope change!

Anyhow, all my other bikes (n+1 remember) have decent gearing, my favourite being by Ultegra equipped PlanetX road bike which I don't really do justice with my lack of fitness. Anyhow, I enjoy it.

Ben6899

FWIW, that sprocket looks fine...

ugo.santalucia

slowestrider said:

Whilst look for a new sprocket, I came across a couple of sellers on Ebay with as new 6 gear rear wheels, from people exchanging them for the all-black edition wheels for an ok price, so now I've ordered all the bits to turn my M3L to a M6L. Talk about scope change!

Anyhow, all my other bikes (n+1 remember) have decent gearing, my favourite being by Ultegra equipped PlanetX road bike which I don't really do justice with my lack of fitness. Anyhow, I enjoy it.

The 6 speed is basically a 3 speed hub with 2 cogs instead of one.
I went the opposite route, I bought a 2 speed, but then got fed up of the mini derailleur getting jammed with dirt and removed it... now it's a single speed 73 inch, which is adequate to go everywhere short of Winnats pass