You can continue to relube or replace parts of your multi-piece bottom bracket, or chuck it all and replace it with a sealed cartridge. But which one? There are dozens of sizes out there....
For older standard road bike (Trek, Giant, etc.) square taper spindles, you'll probably find something like this: BC 1.37 x 24 x 68 x 117.5. What does that mean? It seems that BSA/BC/ even ISO are identical layout in practical terms. 1.37 is the approximate diameter of the frame bore in inches. 24 is the threading (24 tpi). 68 mm is the bottom bracket width (left to right). Mountain bikes might be 73 mm. You'll find standard right hand threads on the left side, and LEFT HAND (reverse) threads on the drive side. The square taper ends are reportedly JIS profile, which fits most Asian crank arms. Install the drive side first (fully seated), then fit the left retainer. You'll need a Park BBT-22 or equivalent tool to install this assembly.
Spindle length is the tricky part. My old one had threaded extensions with nuts and then plastic dust caps to finish the look. Cartridges are internally threaded, and you'll need to also buy hex head crank arm M8 bolts that include a rubber dust seal. Minus the threaded ends, my road bike spindle was 117 mm long (square end to square end). This cartridge claims to be 117.5 mm. The unpredictable part is that some old spindles don't have exactly the same amount of that 117.5 protruding on each side. Once installed, I had a very slight differential from the original, which increased the chain-line (chain rings pushed out a millimeter or so) which required adjusting the travel limit (H & L) screws on the front derailleur slightly to compensate along with a small shift cable adjustment. A quarter turn of each limit screw and I was good to go!
| Item Package Dimensions L x W x H | 5.67 x 1.77 x 1.69 inches |
|---|---|
| Package Weight | 0.3 Kilograms |
| Item Dimensions LxWxH | 5.6 x 2 x 2 inches |
| Brand Name | SHIMANO |
| Model Name | Square Type Bicycle Bottom Bracket |
| Color | noir/argentà |
| Material | Alloy |
| Suggested Users | unisex-adult |
| Number of Items | 1 |
| Manufacturer | Shimano |
| Part Number | EBBUN300B17X |
| Style | Square Type Bicycle Bottom Bracket |
| Size | 68mmx117.5mm |
| Sport Type | Cycling |
