Originally Posted by
well biked
Post #12 explains things pretty well. The issue is the folding function of the bike, hence the spacers on the drive side that are causing the spline engagement problem. My advice to the OP: go back to square taper on this bike so that you have more leeway with choosing spindle length to work with the folding function of the bike, and no issues with the crank being installed incorrectly, which is the case with the crank in the photo.
This was an experiment. I find the gear selection on a 6 speed Brompton to be inadequate when touring. Quite a few people have a 2X crankset on their Brompton and they seem to work well. I wanted to try it with off the shelf, cheap Shimano parts.
A 73mm MTB crankset would work but as the commenter said, the chainrings are too small.