Cycling UK Forum

Hi, don't know if anyone's run up against this issue.

I’ve put new chain and sprockets on a 6-speed Brompton, but the chain will not mesh properly in the smaller sprocket: it's meshing at perhaps two points on the cog, but not anywhere else.

I thought maybe the sideplates were rubbing on the face of the 15T sprocket, in which case I'd expect the correctly-seated links to be adjacent to the extra-small derailing teeth on the 15T - but I've checked and that's not what it's doing.

I checked the chain width in case LBS messed up there, but inside dimension is ~2.3mm, so that ought to be ok. Maybe the between-sprockets spacer is smaller in the current edition of the sprocket-stack and I should swap the old one back in?

I wondered if it just needed running in, but even with quite a firm push with my fingers I can’t get it to seat, and I don’t want to force it.

I’ve attached some photos here. I’ve also uploaded an 8 sec video here.

I suppose it’s just possible that I’ve messed up the sprockets spacing somehow by altering the hub cover on the offside (I didn’t mean to do this but the gap with my thumb on it seems to have got wider?? Can’t really see how this might affect things tho)

Don't know if any of you can help - but thanks if you can!

Seems odd. I would suggest (assuming you still have them) that you reinstall the old sprockets and chain, see if the problem goes away, then measure all the clearances and compare with the new sprockets and chain, and even with combinations of old and new. That may be enough to identify the problem. Another idea - if you know someone else local with the same setup or the LBS has them - compare to see if there are any differences. Perhaps a spacer has gone missing? Are the links on the new chain sticking a bit perhaps?

Peter H

Are the new sprockets definitely 3/32? I think all Brompton sprockets and chainrings are now to reduce stock but the 3 speeds used to use 1/8.

If the LBS had old stock this could cause your problem.

Gah! I'm sure we've all had these moments but it doesn't make them any less painful...

Just called LBS (Brompton specialists C H White in Malmesbury - +1*1000 for this and countless other instances of help).

So the 13T sprocket has a ridge on one side that serves as a spacer between the sprockets - this in addition to the spacer ring that you have to fit. That ridge has to face inside, natch, but numpty me put it on facing outside. Which entirely explains the lack of clearance between the sprockets.

Thanks both of you for your help. Don't suppose you reckoned on my having been so stoopid... Still maybe this post will save someone else the agony!

Cheers, Ed

As embarrassing as mistakes like this are, it's always a relief to find out it's something so simple that doesn't require more bits/expense. Nice one