Cartridge Bottom Bracket Wrench

If you're tired of your tool slipping out, look no further. The 1671.8/2BI-US is the cartridge-BB tool we built for benchtop work that won't slip under load.

The body combines our 1671.1 cartridge wrench with a 350 mm handle for leverage AND a double-threaded retaining screw that holds the tool against the BB cup as the wrench turns. The double-threaded screw threads into the axle and keeps the wrench from slipping and damaging the bottom-bracket nut.

The result is a tool that engages once, stays engaged, and doesn't cam out at the moment a stuck cup finally breaks loose.

How it's used

Insert the 20-tooth socket end into the BB's splined recess until all 20 splines mesh fully. Thread the additional screw into the axle until the head is held in the cup; that is what keeps the wrench from slipping.

Apply force on the 350 mm handle in steady pressure. On English-threaded frames, which covers most bikes, the drive-side cup is left-hand thread and loosens clockwise; the non-drive cup is conventional right-hand thread. Once the cup breaks loose, finish winding it out with this wrench or switch to the 1671.1/4 socket on a ratchet.

The retaining screw can either be hand-tightened (for routine removal where the cup isn't badly stuck) or driven with a 24 mm wrench (for cups that have been seized in place for years and need maximum engagement against the cam-out moment).

The handle can be removed from the socket head if you want to drive the 24 mm AF screw with a 24 mm wrench or a torque wrench; Unior says the handle can be taken down if necessary.

Compatibility

• Shimano Octalink cartridge bottom brackets
• Truvativ cartridge bottom brackets
• Shimano standard cartridge bottom brackets
• The double-threaded screw is what lets the same head cover Shimano standard, Shimano Octalink, and Truvativ cartridge bottom brackets

Specs

• Material: premium flex plus carbon steel
• Surface finish: trivalent chrome plated
• Handle length: 350 mm
• Spline count: 20-tooth
• Includes: integrated handle (removable), double-threaded retaining screw, 24 mm wrench-flat on the screw for tool-driven snug

Built in Zreče

Unior has been forging hand tools in Zreče since 1919, and sponsors professional road and mountain-bike race teams. The double-threaded screw that threads into the axle is the design call that earns this tool its keep on seized cartridge cups; Unior's service manual reaches for the 1671.8/2BI when a socket alone cannot hold.

Pro tip from our mechanics

Removable handle is what makes this tool a genuine bench piece rather than just a longer wrench. On a torque-controlled install, take the handle down and drive the 24 mm AF screw with a torque wrench. Unior's service manual lists 50–75 Nm for square-cartridge cups and 50–70 Nm for Octalink cups. Reattach the handle for the next removal job; the tool covers both directions of the BB-service workflow.

Cranks come off before this wrench can reach the cups. For interface identification and the puller that precedes this job: How to remove a crankset →.

FAQ

Which bottom brackets does the 1671.8/2BI-US fit? Unior lists Shimano standard, Shimano Octalink, and Truvativ cartridge bottom brackets. The double-threaded screw is what lets one head cover those axle types. It is not the 8-notch tool (that is 1671.2/4) and it is not the wrench for Hollowtech II-style external cups (1671.5/2BI or 1609/2BI).

How does the retaining screw work? You thread the additional screw into the axle. That holds the wrench in the cup so it cannot slip and damage the nut. The screw is 24 mm AF and takes a 24 mm wrench or a torque wrench. Unior's official method is to thread the screw into the axle; the datasheet does not describe a self-adjusting spring.

Which way does a cartridge bottom bracket unscrew? On English-threaded frames, which is most bikes, the drive-side cup is left-hand thread and comes out clockwise; the non-drive cup is conventional right-hand thread. Italian-threaded frames use right-hand thread on both cups. Unior's service manual starts the job on the left side and reaches for this handled wrench when a socket alone cannot hold.

Can I take the handle off and use a torque wrench? Yes. Unior says the handle can be taken down if necessary. Drive the 24 mm AF screw with a 24 mm wrench or a torque wrench; the same procedure is used for installation. The service manual lists 50–75 Nm for square-cartridge cups and 50–70 Nm for Octalink cups.