I pulled my bottom bracket out today to replace it, and I didn’t like what I saw when I looked inside the bottom bracket shell. There are little grooves and scratches in there, running transverse to the threads, running all along the upper side of the shell. They’re irregular enough that they don’t look like they are supposed to be there.
Also when I pulled the bottom bracket out some aluminum shavings came with it, and one of the sides of the bottom bracket has scratches that make it look like its been stuck in a lathe.
Thirdly, when I looked at the device that holds the cables on the underside of the bottom bracket, I noticed that one of the screws does not have a nut underneath it, while the other one does. The one without a nut is jutting into the shell maybe 3 mm as a result.
My current hypothesis is that the screw scratched up the bottom bracket, and then the shavings in turn scratched the shell, but I’m really just speculating. So, I have the following questions. (1) Does anybody know what is going on? (2) If a screw is jutting into the shell, will it touch the bottom bracket? I saw some pictures online that had jutting screws, but they didn’t use cartridge bottom brackets. (3) What will become of my frame? Can I get bike shop to repair the shell, or do I need a new frame? What effect will these grooves have in the short term?
I appreciate any insight.
Edit: Looking more closely at the bottom bracket, I can see the indentation from that screw, and the lathing continues from there. I guess the person that built the bike must have done it.
What frame do you have? Incidentally, I pulled the ISIS BB from my P2k to replace the BB/cranks, everything looked fine after 6000+ mi.
After replacing the BB/cranks, I noticed the screw holding the plastic cable guide had a nut there acting as a spacer. Not making the connection that it may be protruding into the BB shell far enough to cause damage, I took the nut out and screwed the cable guide in. The screw didn’t seem to ‘bottom out’ onto the BB “pipe”, and I slapped it on and went on with my business.
I’m eager to see responses to this thread and how necessary that spacer nut is to internal BB damage.
I think that screw is definitely the culprit because of the screw-shaped imprint on the BB. The BB “pipe” looks like it’s made out of aluminum, which is a soft metal, so I can see how putting the screw in too far might go unnoticed.
The scratches were most likely caused by the cable guide screw going in too deep. If the screw was indeed the culprit you would have had to remove it to get the BB our or else it would have been stuck part way as most BBs have an hourglass shape to them.
The frame is probably OK. Take it to your LBS and have them chase the threads of the BB shell with a tap. Get a new BB and put the screws to the cable guid in after the BB has been installed. Everything should be OK after that. Or use shorter bolts for teh cable guide.
Thanks. It has a half-hourglass shape. I wasn’t sure what that was all about, and I don’t know whether the hourglass part is on the drive or non-drive side.