LBRY Block Explorer

LBRY Claims • shimano-hollowtech-ii-bottom-bracket-2

a8676a0d6a2a4b750f0333f9e191f93ace0ab69e

Published By
Created On
8 Jul 2020 16:10:38 UTC
Transaction ID
Cost
Safe for Work
Free
Yes
Shimano HollowTech-II Bottom Bracket Narrowing, Part 1
Replacing bottom bracket bearings and narrowing the crank Q-Factor (or tread) while I'm at it.

I installed a Shimano SLX M660 9sp MTB triple crank set on my monster cross when I built it 5 years ago. The frame I used specified an MTB crank for clearance at the chain stays and I also wanted the 58mm BCD on the small chain ring so I could fit a 20T chain ring there.

But the MTB bottom bracket is supplied with 3 - 2.5mm wide spacers, 2 for the drive side and 1 for the non0drive side on a 68mm bottom bracket. This sets the triple crank chain line out about 50mm from the center. With a 10sp cassette and 130mm rear axle, the center is about 45mm out from the center, a bit more on a 135mm axle. I wanted to get the front chain line closer to the frame, so I omitted the 2 - 2.5mm spacers on that side. Instead of one spacer on the other side, I needed to use 2 to take up the extra spindle length.

This worked OK, but it did leave the left crank offset 5mm farther from the frame than the right crank. This wider Q-Factor also make pedal strikes on that side more common.

When I noticed the bottom bracket bearings making noise, this seemed like a good time to revisit narrowing that bottom bracket down as much as possible. The first step is to machine out ~5mm of female spline from the inside of the crank arm. This leaves 11mm of spline left to engage the spindle. I used a 15/16" drill bit and took out 0.200" (5mm) of splines. A Dremel tool and cutter was used to clean up the splines left until the spindle extended 5mm beyond the crank arm.

A decent drill press should be able to do this job. Or given some time and care, it could all be done with a rotary tool like the Dremel. Just mark how far down the splines you want to go (5mm) and then slowly run around and around until the splines start to disappear. No need to cut them completely away, just enough until the slide over the spindle.

Sheldon Brown's (RIP) excellent articles on chainline:
https://www.sheldonbrown.com/chainline.html
and Q-Factor:
https://www.sheldonbrown.com/cranks.html#tread

A few articles on narrowing the bottom bracket:
- http://forums.mtbr.com/drivetrain-shifters-derailleurs-cranks/xt-hollowtech-ii-high-q-factor-260152.html
- http://www.recumbents.com/forums/topic.asp?TOPIC_ID=5097
- http://faqload.com/faqs/bicycle-components/drivetrain/xt-m760-761-cranks-shrinking-the-q-factor

More to come, dealing with the exposed spindle splines and replacing the bottom bracket bearings:
https://youtu.be/V5pomMoN5ls

Be sure to rate, comment and share
And as always, thanks for watching

Intro:
Louisiana Fairytale by Austin Rogers
http://drfiddle.com/show_tune.php?id=94
...
https://www.youtube.com/watch?v=2Xd24uac4hM
Author
Content Type
Unspecified
video/mp4
Language
English
Open in LBRY

More from the publisher

Controlling
VIDEO
TOYOT
Controlling
VIDEO
NEW I
Controlling
VIDEO
JAZZI
Controlling
VIDEO
HALLO
Controlling
VIDEO
BREVI
Controlling
VIDEO
WATER
Controlling
VIDEO
TRYIN
Controlling
VIDEO
EASY
Controlling
VIDEO
FILAM