So, the story goes like this.
- A Brompton rider bought a Token square taper BB and was using it for a while along with the original crank and chainring without any issue;
- The rider subsequently bought an Absolute Black brand of oval chainring and wanted to use it on the Token BB with the original crank;
- He took the Absolute Black to a shop to get it installed;
- It didn’t workout, the chainring bolts that sit inside the chainring were rubbing the rear triangle when it was folded;
- According to the rider, 3 pieces of spacers (2mm each) were added to the crank side of the BB and the chainring bolts were still in contact with the rear triangle when the Brompton is folded;
- The original BB was then restored, but we are still having one chainring bolt rubbing the rear triangle and it was removed as a quick way out.
There are 2 parts of the problems that we have here.
First, why did the chainring bolts get into the way after changing into the Absolute Black chainring?
Everything is happening for a reason and everything is there for a reason. When the Brompton came in, one of the chainring bolt was removed to avoid it from rubbing the rear triangle when the Brompton is folded. I don’t agreed with this kind of quick way out as it would cause danger to the rider.
There was a missing chainring bolt when the Brompton first came in.
The Brompton stock as well as many after market chainring are usually in 3mm thick. The Absolute Black chainring measured at 4.67mm. That extra bit of thickness could be the answer to our problem here.
The thickness of the chainring is thicker than the usual one.
Secondly, we wanted to figure out why the installations didn’t work out even with 3 piece of spacers (6mm) being installed on the drive side of the BB.
I had installed more than fair amount of BBs on Bromptons, be it the square taper type or the road bike’s hollow-tech type. Unless the information were given wrong, otherwise, I had never heard or seen 6mm of spacers being used at the Brompton. Anyway, in front of us there is this Token BB that were pull off from the Brompton after the previous installations.
Usually the drive (right) side of the mounting cup is secure to the bearings and its rather hard to pull it out by hand, but the used one in our hand seems having the right side cup pulled out for the spacer’s adding and subtracting. Assuming the left side of the cup is stationary and the axle was aligned to it, there won’t be any difference if any spacers were adding on. It will be just the drive side mounting cup moving in and out but not the main axle. If this was the case, there will be 2 downside of it. First, the BB axle really didn’t shift to the drive (right) side, hence we are not creating the necessary space between the crank and rear triangle when the Brompton is folded. Secondly, as the mounting cup got pushed out by the spacers, there will be rooms left inside for the bearings to shift around within the empty space, the bearings tend to have shorter life spam if they are able to move around.
Anyway, it didn’t take long to get the problem solved here. A single 2mm spacers on the driver side did the job for us. The rider is having fun with the Token Ceramic BB and Absolute Black chainring now.
A 2mm spacer is added to get the work done.
A good healthy spacing of around 2mm away from the rear triangle when the Brompton is being folded.
