StumpHunters Cycling and MTB page

The Bottom Bracket is rather the unsung hero of the average bike, everybody will sit and admire your XT rear mech but tell them you have a XTR bottom bracket and nobody is interested. The Bottom Bracket - highly ignored (well you can't see it) is highly important, its the bit that takes all the abuse of your jumping, heavy pedal style e.t.c e.t.c. Me being me I probably wont update this page for a couple of years so I'm not going to say XT,XTR I'm just going to say Splined and Tapered. Tapered bottom brackets are the old style square spindles where the crank is held on by force/friction. Splined are a more circular spindle and look like a cog/jockey wheel with square teeth.

Removing Chainset - Tapered axles

First off you will need to remove the crank bolts, most can be removed with a 8 mm Allen key but sometimes a nut is used instead so you will need to use a socket kit to remove these. These bolts tend to be on tight so don't worry if you have to use large amounts of force (but make sure you are going the right way). Once you have the crank bolts removed check that there are no washers in the crank. You should be able to see the square axle.
Now its time to remove the cranks ... do not hit the cranks with a hammer from the back under any circumstance, blocks of wood and the like will not help, use a crank extractor.
Before inserting the Crank Extractor clean the treads of the crank and then apply a little grease to the threads so that the extractor is correctly positioned.
Wind the 'pusher' the bit in the middle of crank extractor all the way out and then wind the crank extractor into the crank ... make sure that it goes all the way in as the crank is fairly soft and if it doesn't have enough grip it will just strip the tread from the crank and you will have one nicely mangled crank
Once the crank extractor is fully inserted wind the 'pusher' in and it will push the crank off the bottom bracket.
Repeat for the other side.
After removing a tapered Chainset always check the Chainset for damage, the whole that the spindle fits into should be square ... and check for cracks appearing

Removing Chainset - Splinned axles

You should be able to remove this with a simple 8mm Allen key as they come with self extracting crank bolts. With self extracting crank bolts the bolt will be tight, go soft and then tight again as the bolt begins to push the crank from the bottom bracket.
If self extracting crank bolts aren't used then they can be removed with a ordinary crank extractor as outlined in the bit about about tapered cranks ... but the bottom brackets tend to be hollow so you may need a crank plugger so the the pusher has something to push against.

With the bike the correct way up (wheels at the bottom) to following tightening directions are to be used

Both Splined and Tapered bottom brackets can be removed with a standard Bottom Bracket tool, the only thing to look out for is the fact that the Splined Bottom Bracket have a larger axle so the whole in the center has to be larger in order to make sure that you have enough clearance, all new tools should have enough clearance.
Before explaining how to remove the BB a couple of words of advice. Clean the cups (where the Bottom Bracket tool fits) to make sure that you don't get any slippage as damage to the cups will mean that removing the BB is very difficult. Before turning make sure that everything is secure, if the BB is tight and/or you are worried about the BB tool slipping it is sometimes possible to bolt the tool to the and to the BB by using one of the crank bolts and a large washer.
Remove the Crank side first.
Remove the none Crank side.
Clean out the BB shell, if moisture is inside the bike try and find out where it is coming from. Such as leaving the water bottle bolts out of the frame.
Before inserting the new BB Grease the threads, place the none crank side in first but only a short way.
Place the Main Body into the crank side and start by hand, it is important (as always) not to cross thread. After a few turns and you are sure that you aren't going to cross thread start using the BB tool. The cup should fit snugly into the frame, about 50Nm if you have a torque wrench,
Once the Crank side is snug wind the none crank side, if disappears into the shell or any thread is left showing then you have the wrong size bottom Bracket.

Well Shimano have really done a good job on this one, Bottom brackets are now sealed unit's - if they brake - replace. They are so cheap that it's the easiest way, and being sealed units they are less likely to be impregnated with all the grit and grime that the bottom of your bike goes through out on the trail

The Bottom Bracket - Under Construction

Removing Chainset - Tapered axles

Removing Chainset - Splinned axles