BOTTOM BRACKET REBUILD - INTRODUCTION

The bottom bracket (BB) consists of a spindle which goes round and round.  The bicycle's cranks are attached directly to the spindle.  The spindle rides on ball bearings which in turn ride in a set of bearing cups.  The whole assembly swims in grease.  It is important that there is as little friction as possible when all this stuff is happening.  It is also important that this all happens where it is supposed to.  With this in mind, components must be in good condition, well lubricated and properly adjusted.

The bottom bracket housing that contains the bottom bracket assembly is located at the bottom of the bicycle frame where the seat tube and down tube meet.  This hugely important and delicate assemble is always in harms way for a variety of reasons.  It is close to the ground and splashing water can easily enter the cavity causing delicate internal working to rust.  Many vintage road bicycles are fitted with open seat posts, which will also allow water and road debris to enter the bottom bracket cavity.

Bottom bracket maintenance is very important and should be conducted at regular intervals.  I ensure that I clean, inspect, lubricate and adjust my bottom bracket(s) at least once each season.  Additionally, if the bicycle I am riding gets really wet, it is time to open up and maintain the bottom bracket.  If the bottom bracket starts making runch runch sounds, it is time to maintain the bottom bracket.  If I ride one particular bike a great deal, it gets more attention than do less ridden steeds.

If you take the time to ensure that the bottom bracket is well maintained, it will last for a very long time and work almost perfectly.  If you fail to look after the bottom bracket, its life expectancy will be quite short.

Basically, there are two types of bottom brackets associated with vintage road bicycles.  The Old School bottom bracket is of cottered design.  This style of BB secures the cranks in place with a pair of cotter pins, one for each crank arm.  This Old School system is certainly the less desirable when performance is the issue, but properly installed and maintained the cottered system is just fine.  To that add the fact that the cottered design screams vintage appeal.

The more modern BB is referred to as the tapered design.  This style uses a spindle with square tapered ends which fit into matching tapers on the crank arms.  Maintaining this style of bottom bracket is much easier to do, however at least one special tool is required to remove the crank arms.  Additionally, the tapered BB allows the installation of alloy crank arms.  Though possible with cottered systems, the results of installing an alloy crank on a cottered BB is less than desirable.

The soft alloy of the crank arm will wear rapidly on the cotter pin and slop will soon develop between the BB spindle and crank arm and it will be the crank arm that develops the wear.  Replacing crank arms can be a costly endeavour.

There are different thread sizes associated with bottom brackets depending on where they were made.  French made brackets will not fit English housings.  Nor will they fit Italian or Asian.  It is wise to take the time to determine what size and length you will need before purchasing a replacement BB assembly.

Overall bicycle performance is dependent on a variety of situations.  One of those situations is the condition of the bottom bracket.  If performance and best ride are the targets, always go with a quality bottom bracket.  It makes little sense to me to build up a really nice vintage road bicycle with the best of everything that can be seen and then install a cheap bottom bracket.  Go with the best that you can afford.

NEXT - REMOVING THE BOTTOM BRACKET