Shimano FC-9000 crank in Trek BB90 bottom bracket fitment

Discuss light weight issues concerning road bikes & parts.
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Gearhead65
Posts: 112
Joined: Sat Jan 23, 2010 1:24 am
Location: Evansville, IN, USA

by Gearhead65

I'm building up an Madone 7 for a friend and installing an FC-9000 (Dura-Ace) crank in the BB90 bottom bracket. With the bearings fully seated, it appears that the leftside arm does not slide onto the crank axle quite as far as I have experienced on other bikes I have built in the past.

Researching BB standards, the BB90 appears to be the widest at 90.5mm for road.

Thus on a related note, Shimano also sells two (2) different crank fixing bolts. (Version 1 and Version 2). The difference is thread length. Version 1 thread length is approx 8.5mm and version 2 is approx 16mm. I am assuming the version 2 is for these situations where the slightly wider bottom bracket causes the crank arm to engage on the splines slightly less.

Waiting on the crank fixing bolt to arrive (ver 2), but asking for input to see if I'm interpreting this correctly. Engagement of the arm on the splines seems to be about half, although that appears to be per design?
2015 Specialized Crux Pro
2013 BMC TMR01 custom build
2013 Cannondale F-Series 29'er, Carbon 3
2012 Cannondale CAAD10-1 custom build, 14.06 lbs
1980 Palo Alto custom build

by Weenie


crimsonbadger
Posts: 85
Joined: Tue Oct 25, 2011 4:50 am

by crimsonbadger

Strange.

Give the DS crankarm a light tap with a rubber mallet--make sure it's all the way in there.

leonvl
Posts: 6
Joined: Wed Jan 30, 2013 6:10 pm

by leonvl

The crank fixing bolt is not designed to lock the crank arm in place. It's only used to apply the right amount of 'pre-load' on the bearings. The two smaller bolts in the crank arm fixate the crank arm on the axle.

So, basically, if the thread on your version 1 bolt engages, you should be fine. Just give the crank a tap like crimsonbadger says.

FIJIGabe
Posts: 1382
Joined: Tue Sep 11, 2012 6:07 pm
Location: The Lone Star State

by FIJIGabe

I recently did this on my 2013 Madone 5 (same BB dimensions). Give the crank a tap with a rubber mallet, and once through, secure the crank (as mentioned above).
Madone 9 https://goo.gl/7UwZpV
Crockett https://goo.gl/f5PdCN
Madone 5 https://goo.gl/cMdyFo

Madone 4, Cobia. I own a lot of Treks.

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