seized bottom bracket

Seized Bottom Bracket

Some 10 years ago I bought my son a decent mountain bike, last summer he returned it to me wanting it serviced for him to use at University. What a wreck! During the initial stages of servicing I found the bottom bracket (BB) to be “grinding”and the axle to be moving around in its bearing housing like a wooden-spoon in a mixing bowl. If the BB could not be replaced the bike would have to be thrown away. This is when I found the BB to be completely seized-up. I spent weeks trying to unseize it by various methods. In the end one method worked “beautifully”.

In the last couple of years I had bought a nice BB removal tool to be attached to a 1/2 inch socket-drive and I nearly threw away my old tool. So glad I didn’t as this was the removal tool that worked; but it was necessary to bolt it to the BB (see photo above). I’ll assume you have removed the chain-set and explain how the removal process works:-

1. Most BBs have an internal “crown” type grip for a fitting/removal tool (see photo below). The cleaner the “crown” is the better, as the removal tool will fit better, and further, into the BB. So liberally spray with a grease dissolving/lubricating product and scrub with an old tooth-brush. Remember to do both sides of the BB.

2. In most modern BBs the drive-side “crown”(that’s the side with the chain) is part of the BB body, whereas the nondrive-side is a circular “shell” screwed-in to the BB frame to make a wedge (the BB in the photo below is of an older variety where both ends are circular “shells”). The drive-side of the BB is, therefore, the most solid side and less likely to be damaged, so start that side.

3. The BB remover in the photos has a hole running through it, so with an appropriately sized (strong) washer it is possible to use the BB’s own chainring bolt to bolt the removal tool to the BB (see photos).

4. When you have got this far use an adjustable wrench (most of us have an 8 inch wrench, but consider using a 12 inch wrench (a very useful tool and much more “muscular” than the 8 inch). The drive side BB has an anti-clockwise thread (see note below regarding English/Italian threads). This means that to undo it, it must be turned clockwise. In practice this is quite useful as both sides can be undone by turning the wrench in the space between the 45 degree downtube and the forks.

5. Time to stand on the 12 inch, muscular, adjustable wrench. Don’t worry about damaging the BB shell (the part of the bike frame the BB passes through). Consider the forces the frame endures when a strong 12 stone man gets out of the saddle to beat the traffic lights. In any event, if the frame is going to break, better it break in your garage rather than when being ridden on the road! Gently bounce on the wrench to get the BB “crown” moving. Unless you have a long chainringbolt and have been able to put 10 or more complete turns into the BB axle, undo the drive side only 2 or 3 complete turns. The reason for this is that you are pulling the BB axle through the frame and as the nondrive-side “shell” has not moved, the bolt length will have to be longer when bolting in to the nondrive-side BB axle. Even if you do have a long bolt you still need to be able to bolt the removal tool to the nondrive-side to remove that “shell”.

6. Unbolt the BB removal tool and bolt it to the nondrive-side “shell” and completely remove that “shell”, then re-bolt the BB removal tool to the drive-side and completely remove the BB unit. Job done, well done!

Want a few more tips? Tip for metal frames only

a) Why did the BB seize in the first place? Likely to be because of water ingression. Drill a 3mm drain hole in the centre of the BB at the lowest point, before you fit a new BB. If there is already a hole, make sure it is clear and remove any plug.

b) Carefully and thoroughly clean out the BB thread to aid fitting a new BB and prevent re-seizing.

c) Take very great care when fitting a BB as it is so easy to cross thread. I would suggest that you screw both sides in by hand until you are absolutely sure the threads are properly aligned.

d) When the new BB is fitted I would suggest using a low to medium strength thread-lock. This will take up the air space in the thread and so seal out water. Or at the very least use anti-seize grease.

e) On some cheaper sealed BB units the nondrive-side “shell” is made of plastic, meaning it is prone to damage. If you do mangle it, it can be melted out. Before you reach for the blowtorch, I would suggest, you first try a powerful hair-dryer or hot-air paint-stripper.

If you have a really old bike with-out a sealed BB unit and if the above method is not helpful, you could try applying penetrating-oil through the downtube (once the saddle post is removed) or through the seat-tube bottle cage boss (this tip is dependent upon there being access to the BB bracket frame-shell via the seat-tube. You could always have a poke about with a stick down the seat-tube) or through any drain hole in the BB frame-shell, drill a hole if needed (see “a” above).