Brompton M3L Chainring
 

Hi,

The chain ring on my standard M3L Brompton is now ridiculously worn. I'm having to file the burrs off the teeth!

But its made as a single piece with the crank so will cost me nearly £60 to replace. I reckon I should really be replacing the ring every 12 months or so. Loads of money.

Now looking at the spares on the SJS Cycles site it looks as though I can buy a spider crank + a chain ring which will cost be a bit more now but save in the long run. I could also rotate it with respect to the crank to spread the wear.

Are they compatible? Will it match the LH crank I have or do I need to replace that as well?

Thanks
Rob.

Or you can get a road double , and use a metal chainguard on the outside where that ring would sit ..

Surly makes Stainless steel chainrings to 50t, Schlumpf and Bike Friday sell bigger disc chainguards .

I have a Schlumpf MD crank (54t), and a Bike Friday (53t), both use the common 130 5 bolt pattern.


compatibility is about the right side chainline .. not changing , at its most basic criteria

Square taper BB should be in common Between the 2 Brompton sold parts you mentioned.

Last time I checked the spider crank was not sold seperatley i.e. you could buy the rings but not get the spider unless you purchased a new bike!

You WILL need to change the BB for the new spider crank.

I have quite a few of the older ones of various teeth size as they are often found cheap on ebay almost new when people change thier gearing.

I find it strange that it is so worn after 12 months ?

Maybe you are doing thousands of miles a year and not changing your chain when its worn ?

I do about 2000 a year on mine but change the chain as soon as its worn about every 1000 miles or so which as you state is cheaper than changing the crank.

Regads

Jerry

Just checked. There are four old chains hanging in the garage. So on fifth - one every six months or so. Needs a new one for the new chain ring.

Are you sure about the BB? Sjscycles list the spider as a part but show no stock so it may be academic...

Rob.

Hmm. I've never worn out a chainring. I mean, some are worn but not enough to affect performance.

Call Brompton on the Phone and talk to them, they're in your Country. they have telephones ..

as its ordered in Bulk for building the bikes , now, they may sell you one .
or ship it to your local dealer ..

Sounds like you are changing your chain enough then.

I exchanged a few emails with brilliantbikes who provide great service and they told me the spider is not available though that was a few months ago.

I am pretty certain about the BB

http://brilliantbikes.co.uk/brompton...099044016.html


Regards

Jerry

Thanks,
Might be worth taking to the shop I bought it from and asking them. Really fancy separate chain ring. Are there really different tapers on bottom brackets?
Rob.

Yes :)

Sometimes you can get away with it though in my expereince the wrong mix always ends up with the cranks creaking.

See notes from the late great Sheldon Brown

http://sheldonbrown.com/bbtaper.html



Jerry