[yakman]

Hello all,

I am currently building up a Colnago Extreme Power frameset with mostly SRAM
Red components, the exception being the front der and crankset, which are 2010
Force. This frame has an Italian threaded BB shell (obviously), the shell was
professionally faced and has an exact width of 70mm. The install of a Blackbox
ceramic BB went fine and with no issues, or so I thought. Being Italian threading,
the drive side outboard bearings have an issue with loosening while riding. Fine,
I fixed this with some Threadloc (blue). My first crankset was defective and was
replaced by SRAM under warranty. I have a continuing problem with a metallic
scraping noise that appears only when riding. I've removed, cleaned, relubed and
replaced the cranks a half dozen times and the noise goes away for about 20 miles
before returning. There is no side-to-side play in the cranks. I've tried 3 different
ceramic BBs and one Team GXP BB with no change in the noise. Everything is torqued
to spec with a high quality click-type torque wrench.

I've checked the chainline - it's fine. The chainring bolts are fine (and, of course,
they wouldn't respond to a cleaning and relubing of the crank axel and BBs).

I'm about stumped and wonder if anyone else has had a problem that acts
like this?

Oh, I've seen the video posted showing a SRAM BB that made a scraping
sound. His problems seemed to be solved by cleaning and lubing the parts.
I've tried this several times with no lasting effect.

Thanks in advance for any help!

 

[Peanya]

Welcome to the forums. If I recall correctly, some of the SRAM cranksets needed a spacer between the cranks and BB bearings. When reading the title, I was thinking chain rub on the FD, but it sounds like you know what you're doing.
When you hear the sound, see if you can put it on a stand and isolate the sound to ensure you have the right spot (if you haven't done that already).

 

[yakman]

Thanks for the welcome - and the suggestion.

I considered the need for a small spacer. The way the BB/crank is constructed, the seal of each side of the BB contacts a small raised "doughnut" on both the back of the crank face (on the right) and on the back of the left crank arm. When I tighten down the fixing bolt, you can feel the axel bottoming-out as the bolt goes tight very quickly. With a small spacer installed, this pressure comes on more slowly and you get drag on the cranks as the "doughnuts" are pressed into the respective seals. I was wondering if that scraping sound was from light contact between the doughnuts and the seals - not enough friction to make the seals turn but enough to make a noise. The installation directions say that the cranks may be a little stiff at first and will loosen later. Problem is, even with spacer in place to force contact, the scraping sound returned. I pulled the seals and verified that the bearings were well lubed. Maybe I should just keep riding it with the sound happening and hope that it goes away as things "loosen up". That seemed like a sort of lame process and not what you expect from parts like this.

Sorry for the wordy reply but it's a complicated problem, or it appears that way to me.