Bicycle Mechanics - A cautionary tale of outboard bottom bracket cranks...

I built a fantastic commuter bike a little while back, and among my component choices was one of those "new-fangled" outboard bottom brackets...Shimano Hollowtech II. (I like the concept, and the capless look on the right crank.)

I've worked with square taper cranks before, and when I've installed those I generally try to get everything as tight as possible, without being stupid and breaking/shearing anything. Nothing can ruin a ride like a loose crank arm!

When I started to put my new crank on, I...um...didn't read the directions very carefully. Why should I? It was so elegantly simple in concept and execution. I simply checked that the spacers were right, and then off to the races.

I tightened everything down real nice and tight, starting with the dustcap.

Fast forward many months, and there's a terrible creaking from my bottom bracket every time and apply real power to the left pedal. I troubleshoot everything...I lube my pedals, I try different pedals, I check the bolts clamping my saddle. The creaking is still there. If experience tells me anything, it's a loose crankarm, or worse yet a loose bottom bracket.

So I take it apart and lube everything, and this time make sure it's really, really tight. And oh lordy if that creaking isn't worse. Finally I cave and go to the Park Tool website.

Apparently, if you tighten down that dustcap too much, you can side load the bearings. This, by the way, is a Very Bad Thing.

So I started again, and this time used a more delicate touch with that dustcap. Sure enough...creaking gone.

This is my cautionary tale. Truisms from one type of system don't always carry over...and reading directions never hurt even a decent mechanic. And if you're going to get one of these systems, it really is great!

Just don't overtighten that dustcap.

The first time I dealt with the XTR version of the same crank it was being installed on a customer's brand new Yeti ASR, the first one in our shop. When I got to the crank, I followed the instructions precisely, used the prescribed torque ratings, and as far as I could tell, though I did have doubts about the placement and amount of spacers the instructions called for, all appeared well...

...until he brought it back after a test ride because the crank had fallen off.

I double-checked the instructions, pulled it all apart and everything was exactly like it was supposed to be.

Puzzled, I called Yeti's support line and explained the issue. They checked with one of their builders and called me back with corrected instructions, and after checking for any damage (didn't find any, fortunately) put it all back together again and haven't heard a peep from the customer...even after he completed the Leadville 100.

Moral: Instructions can be wrong, and sometimes you need to just trust your instincts.

It's not really a dustcap its a bearing preload adjustment as you discovered.
That's why the directions have a torque spec. When in doubt RTFM.

They checked with one of their builders and called me back with corrected instructions, ...

Moral: Instructions can be wrong, and sometimes you need to just trust your instincts.

So, what was the problem with the original instructions? I installed one of these BB's on a roadbike last week and everything seemed to go fine, following the instructions from Shimano's website. Is there still a problem with their instructions?

Thanks,

So, what was the problem with the original instructions? I installed one of these BB's on a roadbike last week and everything seemed to go fine, following the instructions from Shimano's website. Is there still a problem with their instructions?

Thanks,
In the particular case I mentioned, the instructions were incorrect regarding the number and placement of spacers that determine the overall width of the BB stack, specifically for the ASR application.

If you are ever going to install a headset, be sure to read those instructions first. - TF

I can only assume that "RTFM" stands for "read the ****ing manual."

I can only assume that "RTFM" stands for "read the ****ing manual.";):D

It's not really a dustcap its a bearing preload adjustment as you discovered.
That's why the directions have a torque spec. When in doubt RTFM.

Instructions? Who reads the instructions.

It's not really a dustcap its a bearing preload adjustment as you discovered.
That's why the directions have a torque spec. When in doubt RTFM.

I like how the Park tool BBT-9 has a place for a torque wrench. :rolleyes:

Get one of these and a set of torque wrenches.
http://www.nashbar.com/profile.cfm?category=600099&subcategory=60001228&brand=&sku=21943&storetype=&estoreid=&pagename=Shop%20by%20Subcat%3A%20Crank%2FBottom%20Bracket%2FPedal

http://www.bikemannetwork.com/biking/p/TL8902

Both of these tools come together and are superior to the park installation tools. Of course, both are torque wrench compatible.

On my Park tool for the Hollowtech II, you screw in the "dustcap" with a plastic thumbwheel gizmo at one end of the tool. I assume this is to provide you with something that you can get snug but not wrench tight. I just hand-tightened it with the thumbwheel as much as I could without pain and hoped that matched the torque in the instructions. So far, so good.

- Mark

Okay, let's see the Torque-Wrenches-Are-For-Anal-Retentive-Weenies crowd brush off this one.

:rolleyes:

Okay, let's see the Torque-Wrenches-Are-For-Anal-Retentive-Weenies crowd brush off this one.

:rolleyes:

Tis true...

While I still largely rely upon my "calibrated elbow" (it does click like a torque wrench sometimes) for many tasks, many components now absolutely require a specific torque rating for the fasteners...especially from a subject-to-liability shop perspective. I can't say I'm fond of the requirement...I just think the manufacturer's pawn a bit too much of this off on the shop.

I feel that if their components require a high degree of torque precision, and they put all the liability on me, they should send me a high-end digital torque wrench for free. :D

The spec for the pre-load cap is like 5 nanometers. I had no idea what a nanometer felt like and I also way overtightened the first time.

The spec for the pre-load cap is like 5 nanometers. I had no idea what a nanometer felt like and I also way overtightened the first time.

Those would be Newton meters. 1 Nm ~ .75 lb-ft. So 5 of em ~ 3.5 lb-ft.

Note that this is not an exact conversion, but is quick to remember and figure. Usually torque specs are rounded off to the nearest 5 or 10 units, and then if an alternate spec is provided it is ridiculously given to 2-3 decimal places....one of my pet examples of innumeracy that one is.