Monty's trying to fettle his 2004 3speed Brommie...

[MontyVeda]

The first thing my new (to me) Brommie needs is a new chain.

According the my research, I need an 8 speed chain; 1/2" x 3/32 with 98 links... and the first head scratcher is plainly apparent.



I double checked the box the chain came in, it's definitely 1/2" x 3/32".

The chain ring doesn't appear to be over worn, ie. no shark fin shaped teeth anywhere... so it's gotta the wrong chain for the chainring, right?

I've double and triple checked what size chain i need for a 2004 and all i can see is 1/2" x 3/32"... so what's the problem here?

 

[Gunk]

The 3/32 chain is correct (A Sram 8 speed is my preferred option) Your bike was originally fitted with a 1/8" sprocket that was discontinued (in 2017) To replace the chain you’ll need the 3/32" sprocket which was introduced in 2012, they’re about £15.

 

[MontyVeda]

... Your bike was originally fitted with a 1/8" sprocket ..

If the rear sprocket and chainring are designed for a 1/8" chain, then surely i need a 1/8" chain?

 

[Dogtrousers]

But the chain looks nicely seated from 3-6 o'clock in your picture, but then the links gradually get out of phase with the teeth. That doesn't suggest a chain width problem to me. If the chain was too narrow it just wouldn't seat at all (As I found when I tried to fit a 1/8" sprocket on my fixed gear bike when 3/32" was needed)

You sure it's not a worn chainring?
Is the chain seating onto the sprocket ok?

Feel free to ignore me. I'm terrible at this kind of stuff. If it's possible to buy a wrong sized component then I will always buy it.

 

[MontyVeda]

...
Is the chain seating onto the sprocket ok?
...

Nope, same there too.

I dug the manky old chain out of the bin, cleaned it up a bit and laid them side by side...



it's the distance between the links that's different.

The bottom length of chain is 1/2" x 3/32".
No idea what the top chain size is, but it came off the 2004 Brommie with a Sachs 3 speed hub

My intention is to replace the old chain like-for-like, which obviously is not 1/2" x 3/32"

 

[Gunk]

https://www.halfords.com/cycling/bike-parts/gears-drivetrain-and-cables/clarks-half-link-gold-1/8-single-speed-bike-chain-246046.html

probably not long enough, you’d need to join 2 of them. Brompton no longer sell a 1/8” chain

 

[Fastpedaller]

That looks as though it's a seriously worn chain!

 

[ColinJ]

That looks as though it's a seriously worn chain!

A quick calculation suggests 3+%!!!

 

[MontyVeda]

https://www.halfords.com/cycling/bike-parts/gears-drivetrain-and-cables/clarks-half-link-gold-1/8-single-speed-bike-chain-246046.html

probably not long enough, you’d need to join 2 of them. Brompton no longer sell a 1/8” chain

There's some on Ebay that look like genuine Brompton old stock... but I've no idea what i need now.

That looks as though it's a seriously worn chain!

in post number five?

 

[Dogtrousers]

A quick calculation suggests 3+%!!!

And quite possibly chainring & sprocket to match.

 

[MontyVeda]

And quite possibly chainring & sprocket to match.

The teeth would all have sharp points on the chainring with that much wear.

 

[Gunk]

And quite possibly chainring & sprocket to match.

The 1/8” sprockets are no longer available

 

[Dogtrousers]

The 1/8” sprockets are no longer available

I'm not talking a bout width. I'm talking about pitch.

There's a 1/2" +3% (by @ColinJ 's estimation) worn chain on there. I'm suggesting that the chainring and sprocket may have worn to match.

Just speculating. Could be wrong. I normally am.

 

[Poacher]

Sorry, but it looks like chainring is toast, to match the chain and rear sprocket.
Brompton currently appear to have the spider type crankset in both 50 and 44 tooth options for £45 instead of the usual £90, as priced by SJS and Brilliant bikes. You'll need a new bottom bracket to match, as it's JIS instead of the old ISO on your bike.
https://www.brompton.com/p/731/crankset-50t-in-silver-spider-type?Colour=Silver
https://www.brompton.com/p/722/crankset-44t-in-silver-spider-type?Colour=Silver
Might need to act fast at that price!
BB needs to be 118 or 119mm, if I recall correctly. At first I thought about Spa Cycles' TD-2 chainset, but you'd need to take advice from someone more knowledgeable than I regarding the appropriate BB for that.
https://www.spacycles.co.uk/m8b0s109p4542/SPA-CYCLES-TD-2-Stronglight-Dural-Single-Chainset

Spendy time, I'm afraid!