While cup-and-cone bottom bracket assemblies are still commonly found on cheaper bikes and many road bikes, most
mountain bikes use a
Shimano-style bottom bracket
cartridge. This cartridge is a single unit with the
spindle and
bearings in a sealed metal cylinder. Adjustment and
lubrication are neither required nor possible.
Removal of this type of a bottom bracket requires a crank puller to remove the cranks, and a special splined tool to remove the "cups" holding the cartridge in the frame. When a new BB is being inserted, tighten the drive (chainring) side first, followed by the other side. The drive side is threaded to tighten *counterclockwise*, while the left side tightens in the regular way.