Bicycle Mechanics - Bottom Bracket Puzzler

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trayraynor
11-18-11, 08:15 AM
I recently removed the Shimano Square Taper bottom bracket from my Trek 950 Single Track with the idea I would overhaul and reinstall it.

While removing the unit I noticed the two rubber dust seals (or grommets) were different sizes. The side of the BB that had the smaller, ill fitting seal was dirty and that side of the spindle was pitted compared to the side that had the correct size seal.

I've owned the bike since new, and had never touched the BB prior to this. I have no idea how two sized seals could have been installed... just doesn't make sense.

Now, I want to reinstall the BB but can't find a replacement seal that is correctly sized (see measurements below), any ideas where I can find a replacement? I've checked numerous grommet/seal mfrs and no one seems to have something remotely close to the following sizes; any help is appreciated:

A-Bore: 16.3 mm
B-Groove Width: 4.5mm
C-Groove Dia: 18.3mm
D-OD: 21mm
E-Thickness: 5mm

corynardin
11-18-11, 08:37 AM
Do you know anyone who owns a lathe? Can you tell what material is it made from?
cbchess
11-18-11, 08:45 AM
did you ask shimano? maybe get a replacement BB if this one was assembled wrong or at least get the proper sized seal.

HillRider
11-18-11, 09:11 AM
I assume the bottom bracket isn't a real Shimano part since Trek (and most other makers) tend to use lower cost, no name components in areas where the part is hidden. Therefore, finding an suitable OEM replacement isn't likely.

However, have you considered replacing it with a sealed cartridge bottom bracket. These are low cost, durable and require zero mainrenance.
DCB0
11-18-11, 11:16 AM
How old is the bike? IIRC, Trek started having their Singletrack line welded in Taiwan (instead of brazed in Wisconsin) in the mid nineties (1994?). I have seen some weird things on their Taiwanese assembled bikes - like pre-patched inner tubes and stuff.

Have you considered switching to a cartidge bottom bracket? THey are cheap and long lasting and available in most sizes.