Bottom bracket tool retaining system

Motivation

Anyone who's worked on bikes long enough has encountered the problem of trying to remove stubborn BB cups. Oftentimes, the problem comes down to tool engagement: the wrench or the socket isn't not held securely against the wrench flat or splines, so under great torque the tool simply slips & can damage your parts.

Prior art

Park Tool makes a tool to assist removal of BB cups.

It can operate in these ways:

• external cup type BBs like Hollowtech
• Octalink type BBs with M15 internal thread on spindle
• square taper type BBs with M8 x 1.0 internal thread on spindle
• notable exception: square taper BBs with M8 x 1.25 external threads on spindle

In the case of a cartridge type square taper BB, the drive side cup is fixed to the entire bottom bracket assembly, so separating the drive side cup from the spindle is impossible.

EVT makes an excellent fixed cup remover, but it operates on clamping the offending cup really tightly (rather than using the wrench flats or splines or other torque coupling), which could easily mar or damage the ball bearing surfaces. Fine if you don't want to recycle it.

Design

• uses Lee Spring part number MS24585-1495 as the compression spring
• requires M8 x 1.0 mm x 50-60 mm long hex bolt
  • 13 mm width across flats
  • 5.3 mm head height
  • this will take the place of the typical crank fixing bolt
  • here is the one I'm ordering for rev 1

Parts

On the left is a dummy BB spindle with internal M8 x 1.0 mm threads.

Then comes the spacer, which presses on a socket or wrench to force engagement.

A spring applies constant preload, but can be momentarily overcome by the user to “rachet” the wrench & re-orient it into a better place.

Seems like the typical length of external wrench flats on the cup is 3 mm. Here is a typical double wrench flat fixed cup pattern:

For use with sockets, the spacer can be flipped around, & perhaps that will give a flat face to press the socket on, whilst allowing wrench access to turn the socket.

An unpictured spring comes next. 2023-09-16 I'm waiting on a model of the spring from Lee Spring before I toss it in, so it's absent for now.

Then lastly comes the knob, which adjusts the preload. Inside is a press fit M8 bolt.

Tool capacity

The SPACER can press onto a wrench with a face 51 mm in OD, max, & on a max socket OD of up to 41 mm.

This particular design is hopefully compatible with 20-spline socket tools such as the BBT-22 & the fixed cup wrench HCW-4.

BB spindle dimensions

Sources here:

Compatibility

As of 2023-09-16, rev 1 of this project only supports square taper BBs where the spindle is internally threaded.

Future improvements

• support for M15 internally threaded BB spindles (Octalink & the like)
• support for M8 x 1.25 externally threaded stud type square taper spindles
• think harder about how to use this with BB sockets

2023-09-20: rev 2

• updated assembly to include wonderful square taper BB model (credit to Robert Stein) for better explanation
• updated text to be more explanatory
• tightened fit of knob recess around hex head bolt from 13 mm to 13-.05 mm
• still no model from Lee Spring for compression spring

Here is a better view of the system:

Highlighted in blue is the supposed worst case where the exposed spindle length is super long. The SPACER must be able to reach over this length & press on the tool (wrench or socket) before bottoming out on the end of the spindle).

I determined this length as 30.5 mm per this chart as dimension JR for the longest spindle of 127.5 mm.