Introduction to Bottom Brackets
A lot of older style bikes have two sets of ball bearings in the bottom bracket that the spindle rotates on. Some bikes had the ball bearings mounted in a cage, whilst others just rotated freely within the cones. I noticed on a bike I had some years ago, that the spindle had a lot of play in it. This meant that I could move the pedals sideways and they had a rocking motion when pedalling. There was also a lot of noise when turning the pedals.
This was an older style mountain bike, and judging by the noise coming from the bottom bracket, it probably wasn't worth my trouble trying to adjust the play out of the cranks. What was scary, was that the bike was almost brand new, and I had only ridden about 50 kms on it. The bike store I purchased it from was on the other side of the country, so I decided that I may as well disassemble it and see if I could try and replace the entire assembly with a sealed cartridge unit.
My biggest shock came when I took the cranks off and disassembled the whole assembly. Most of the ball bearings were floating around in the bottom of the frame. One cage had three bearings in it and the other had none. The entire pedalling assembly was operating on these three bearings. My suspicion was that the bike store had probably overtightened something on assembly.
View of the two bearing cages, with only 3 bearings left in one cage.
On close examination of the spindle, I could actually see where the end nut assembly had scored it, as shown in the next photo. Because there was no bearings, it was resting on the end nut assembly. I decided that this just wasn't worth the problems in trying to reassemble and have it happen again.
End nut assembly had scored the spindle on the right hand side in the photo.
So I approached the local bike shop with just the damaged crank spindle to purchase a sealed unit with one the same length. I was able to match it to one that was almost the same length. It was a screw in replacement for the entire old system and being sealed, shouldn't need any maintenance.
Sealed cartridge type bottom bracket.
If you have an older style bike that uses the twin ball bearing sets, and you constantly have to readjust for play in the pedals, it may be worth your while replacing it with a sealed unit. The entire unit screws into the bottom bracket and has a locking assembly that screws in from the other side.
The pedal cranks should fit straight to the spindle. Check this when you take the old spindle to the store to get a sealed unit. After fitting one of these, they shouldn't need any maintenance. No adjustment required.
While the sealed cartridge is a good quick replacement for the ball bearing assembly, the sealed cartridges have their own problems too. Once they fail, the entire mechanism needs replacement. A ball bearing system if set up properly will last for many years and is serviceable, while the cartridge is not serviceable.
