Shimano BB-UN54 Installation

The bottom bracket holds the front gears and crankarms to your bike.

A bottom bracket fits into a hole at the bottom of your bike frame. The chainrings (front gears) and crankarms (the bars your pedals attach to) fit onto the bottom bracket. Installation of the Shimano BB-UN54 bottom bracket can be done at home with a little patience.

Features

The Shimano BB-UN54 is a cartridge-style bottom bracket. It is available in widths of 68 mm or 73 mm. The smaller one fits most bike frames, except those produced in Italy or France. The larger one is for specially sized mountain bike frames. Both come in lengths of 107, 110, 113, 115, 118, 122.5 or 127.5 mm. Shimano also has a BB-UN54 specific for Italian frames.

Installation

Insert the Shimano BB-UN54 into the bike frame (markings indicate the left and right sides of the bottom bracket). Use a bottom bracket tool to hold the non-drive side (the side without the gears) and a wrench on the drive side to tighten the cup of the bottom bracket until it seats tightly. This process tightens the cup on the other side at the same time.

Considerations

Before installing a new bottom bracket, clean the hole in the frame and apply a little cycling grease to the inside of the hole. Be sure your new bottom bracket is the appropriate length. A bottom bracket that is not the correct length will lead to problems with shifting that are difficult to remedy.

References

• Shimano: Cartirdge Bottom Bracket
• Park Tool: Bottom Bracket installation
• Sheldon Brown: Bottom Bracket Sizing