There are times when you find your Brompton rear triangle had some paint work scratched off (like the first image below) after installing an after market crank-set. Chances are your crank were installed wrongly on your Brompton.
When the Brompton rear triangle is being folded into the main frame, the crank-set would come right next to the folded in triangle. If the crank wasn’t installed correctly for the Brompton, part of the crank would came into contact with the rear triangle. Hence the paint work get scratched off. Sad, really.
What did we do to make it works and look nice again?
First, we had the Brompton rear triangle re-coated with the same tone of color before putting it back onto the bike.
Most bicycle (Non Brompton) are designed to have the bottom bracket and crank system fitted directly for a trouble free usage. In the case of Brompton, the bottom bracket area were offset. If we were to directly installing the crank on the Brompton, the chainring will just rub onto the rear triangle when it is half folded.
One of the common fix to this is to apply spacer to “push out” the right side bearing cup. This way we will be having more clearance for the crank set. In this case, I had added a 2mm spacers to get the job done.