DIY Bottom Bracket Overhaul
External bearing bottom brackets have been around for a good number of years now and, for the most part, they have proven to be quite durable. I’m sure that most will agree that they are generally longer lasting than the internal bearing ISIS and Octalink bottom brackets that came before them.
While that may be the case, bearings will always need some maintenance—especially in the potentially wet and muddy world of mountain biking. The only variable is how frequently the maintenance is required. Some fair weather bike riders may never need the knowledge that I’m about to impart, but those who ride lots, or live in a damp part of Oz could well find themselves with a bottom bracket that is in need of some attention.
As far as some manufacturers are concerned, when the bearing wears out, you just buy a complete new bottom bracket—just as you did with the ‘cartridge’ style bottom brackets of old. Many have the words ‘Do Not Disassemble’ marked clearly on them to stop you tinkering with them. This may sound like a money making scheme to some, but with most units costing around $70 it’s not so terrible. That said, it can add up if you are a frequent bearing killer and some people just like to repair what they’ve already got.
There is an alternative if you want to breathe new life into your existing bottom bracket. Modern external type bottom brackets rely on commonly available industrial bearings (get them from any bearing/ engineering shop). A pair of replacement bearings will cost around $30—less than half the cost of a new bottom bracket. The tricky part is removing the bearings from the alloy cups that they are pressed into.
Phil Wood, RaceFace and Enduro all make specialist tools that will remove the bearings from the cups. At the moment the Enduro tool is the most commonly available in Australia—it can be purchased from bike shops and www.diymtb.com.au for around $135. This tool will extract the old bearings and press the new ones in. The only thing it lacks is a tool for removing the nylon dust seal that covers the outer part of the bottom bracket. This isn’t really an oversight as it is made with aftermarket ‘Enduro Bearings’ in mind. Their bearings eliminate the pesky plastic covers that are fitted to most Shimano, FSA and Token bottom brackets. Each kit comes with easily removable rubber wiper seals to replace the fragile plastic items and the bearings feature a smaller inner diameter—this allows the inner race to sit directly on the spindle without the plastic cover/sleeve. The smaller inner diameter also makes room for slightly larger balls in the bearing race for better durability. Just make sure that the bottom bracket shell on your frame is accurately faced; the lack of plastic inserts makes the system less forgiving of misalignment.