Bicycle Mechanics - Why won't the Bottom Bracket Cartridge thread all the way?
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09-11-12, 06:45 PM
1988 Trek 360 road frame, True Temper. 1.37 X 24 is stamped on the bb cups I removed (Hatte?). Shell is 68mm and bb is 113mm. So I have a newly purchased Shimano UN55, 68 X 113, 1.37 X 24. Goes in drive side and counterclockwise threading. But I can only get about 5 turns and it stops, even cranking hard. Half of the threads are sticking out.
Yet, the removed bb cup and be rethreaded with no problema. I don't believe there are any protrusions in the shell.
09-11-12, 06:55 PM
Have you taken the time to thoroughly clean the bottom bracket shell threads both non-drive and drive side?
Have you taken the time to chase them - such as with a nice clean leftover cup with sharp well defined threads?
Cleaning, inspection, chasing are pretty common steps that are practiced as part of a bottom bracket replacement to minimize install mishaps.
Take the trouble to cover that before considering obstructions/protrusions - unless those are obvious and outright visible to the naked eye.
As to issues specific to Shimano cartridge units, only do 1-2 per year at best. Other folks here do 'em all the time. They'll be along...
09-11-12, 07:15 PM
chase the threads.
Before doing anything else try this test. Thread in either cup (or half) alone, first the right, then remove it then the left. This will confirm that the threads alone are OK and extend far enough.
Now for the tricky PIA problem, depending n the type of cartridge you have. If the cups are a tight fit on the cartridge, they have no ability to float. Now if the threads on both sides of the BB shell aren't precisely on the same axis - you can sometimes see this when you thread in the cartridge and find that it's off center on the opposite side - both cups are no longer pointing directly at each other and so will tend to bind between the mis-aligned BB threads and the aligned BB cartridge.
There's not much you can do, but I've found 2 tricks that help about 90% of the time depending on the extent of mis-alignment.
1- grease the %$#& out of the insides of the cups and outside of the cartridge where they slip over, and the threads of the BB.
2- install the right side first, but not all the way, and DO NOT TIGHTEN. this allows a bit of float and may be enough for you to get the left side most of the way home. Leave enough room for the right to now be tightened home, then tighten the left. If your BB has a plastic side and metal side, save the metal side for last because it can take more wrench stress.
3- for the worst mis-aligned, try working both sides in together toward the middle, this often works when all else fails by splitting the difference in mis-alignment.
4- if all else fails, look for a cartridge BB system with a bit more float designed in. Or have a good shop retap the shell using taps which are linked via a common central shaft.
09-11-12, 08:56 PM
Thanks for the tips guys! Cleaning by reinstalling the old cups with grease is the trick. Also, the alignment advice above is very helpful as well. I'm within a 3 mm of completion! Fresh start in the am.
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