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cranks for square tapered BB

Posted: 3 Jul 2013, 1:12pm
by mig
a little hard to describe but is there a standard orientation in which the holes in cranks are cut for square tapered BBs?

a friend bought a left hand crank in the hope of matching it to an existing chainset.

the hole in the left crank was cut with the 'square' rotated 45 degrees to the chainset's own 'hole' hence giving the effect that the cranks on either side weren't parallel when fitted.

did he cop for a dodgy crank? or do manufacturers merely line up the holes in their own sets? does this by any chance differ for tandems?

(apologies if you are now confused!) :oops:

Re: cranks for square tapered BB

Posted: 3 Jul 2013, 1:17pm
by hamster
Typically the corner of the BB square points in line with the crank arm - Campag, Shimano, Sugino, Middleburn are all like this, at least for things made in the past 15 years. There are a few (as you have discovered) which don't.

Re: cranks for square tapered BB

Posted: 3 Jul 2013, 2:24pm
by mig
why oh why oh why!!! :)

next you'll be telling me that manufacturers make cassette sprockets slightly different widths apart and stuff like that...... :!:

Re: cranks for square tapered BB

Posted: 3 Jul 2013, 10:12pm
by Brucey
the two configurations are often known as 'diamond' (the most common) and 'square-on' types. Quite a lot of the inexpensive suntour cranksets fitted to MTBs are square-on types, and there are a few others.

Yet another trap for the unwary...you just need to check to be sure....

cheers

Re: cranks for square tapered BB

Posted: 4 Jul 2013, 9:07am
by mig
annoyingly it was a rear tandem left hand crank in 172.5....i can't remember the brand....but it wasn't a cheapo!

Re: cranks for square tapered BB

Posted: 5 Jul 2013, 2:45pm
by WOOLIFERKINS
Don't forget there are two different "standards" of taper as well