I run a set of Middleburn sqr taper cranks on a Shimano UN54 bb.

Picked up a Royce bb s/h – the cups are fine, same english thread but the axle is about 1mm shorter and the tapers on the axle dont seem to allow the crank to pull onto the axle to the same amount – looks plain wrong in fact.

The below article seems to suggest an ISO crank on a JIS axle – can that be right? Wouldn’t the UN54 be JIS?? Wouldn’t the Middleburn cranks be JIS???.

http://sheldonbrown.com/bbtaper.html

edit: i’ve just tried an old Shimano crank on the Royce axle and that pull up like it should.

More of a Retro Bike query?

shimano bb will definately be JIS.

http://sheldonbrown.com/bbtaper.html

this should help.

seen that article but i would have thought that the M’burn was also an JIS taper??

No reason for Middleburn to be JIS, but I don’t know what they use. Same with Royce. Phone them and see?

JIS and ISO use the same taper, but with ISO finishing at a narrower point, so what you say sounds right for the Royce BB to be JIS. ISO is becoming fairly uncommon. Even Italian companies like Miche are switching to JIS for track cranks, so they can get cheaper far eastern parts.. Campag still use ISO though.

Mix and match does work, sort of, for both ways though as long as the crank bolts don’t bottom out.

Last time I got a royce bb they were still doing campy (ISO ) and normal ones

So the bb could be either ,what length is bb ?

For some reason I thought mixing iso and jis only worked reversibly one way round but don’t remember…