I've written an extensive history of the BB previously on this forum but I can't find it now.
@Yellow Saddle said last autumn:
"It is a design issue, hardly at all a fitment or component (bearing) problem. The BB has a very chequered history and I'll quickly recap.
First we had cotter pin. Cotters were problematic but were eventually replaced by the square taper, which was brilliant. It allowed lightweight aluminium cranks to be securely fastened to steel crank spindles without any problems of precession and lash, both problems with the cotter. (Note that I'm referring to a British cotter, not American cotter).
"Then the weight weenies came around and questioned the solid BB axle and asked for something to be make lighter. Shimano responded with the Octalink BB. It fitted into existing BSA BB shells and thus didn't require a frame redesign. However, the enlarged axle required smaller bearings so that the assembly could fit into the limited space inside the BB shell. This reduced the bearing durability. Further, the advent of MTBing meant that people now jumped their bikes whilst standing on the cranks one foot forward, one 180degrees to the back. This put huge strain on the axle and the short Octalink spines could not provide enough stiffness and the flex inside the splines caused the crank bolt to unscrew on the one crank pointing backwards. Visualise this is the bolt head moving backwards with the flexing inside the crank eye but not returning with the backlash. This caused the shallow splines to strip. In addition to that problem, the splines were blind and assembly had to be very accurate, otherwise the spindle peeled pieces of spline and ruined the spline as the bolt is tightened. Then Shimano invented Octalink II without acknowledging the mistakes of what was not suddenly Octalilnk I. Octalink II solved the lash problem but not the bearing problem. Shimano even attempted to use roller bearings in its high-end Octalink cranks but these failed prematurely as well since roller bearings don't work well in grease where the grease is pushed away from the bearing and not returned as with a ball bearing.
"Then a repeat of the Betamax vs VHS story started. Shimano refused to license Octalink (or the Americans refused to buy a license) and a consortium of American companies then reverse engineered their own version of Ocatlilnk, called the ISIS spline. It had not 8 as in Shimano, but 9 splines and a different spline shape. This all to avoid patent licence fees. Octalink, Octalink I, Octalink II and ISIS is all rubbish.
"Shimano then decided that it will re-invent the BB again and came up with Hollowtech. This was a two-piece crank with a 24mm spindle and an externally mounted pair of bearings. The crank press-fit into the bearings, separated by a plastic spacer between crank and bearing race. The idea was to save weight, provide a stiff spindle by going oversize and create larger bearings but place them outside of the still-standard BB shell. Unfortunately the spindle was not stiff enough and the left hand bearing now fails prematurely because the spindle flexes on the left. Remember that torque is only transmitted through the spindle from the left crank, not the right. For a long time people through their left BB cup failed because a bike is laid down on its left side and water inside the BB was damaging the left bearing. However, it was the flexing spindle that pulls the sensitive deep groove bearing to run against the sides of its grooves and bind. Also astonishingly, the bearing balls were still too small for the job. Although the bearing diameter increased, the balls stayed small and they packed more of them in rather than bulk up the assembly a bit.
"A BB redesign was called for and national pride meddled with good design. Cannondale, Bullseye and some other American companies then perpetrated BB30. It had a large (30mm) spindle to prevent some of the flexing found in Hollowtech and to supposedly save the customer maintenance cost, fitted two standard industrial deep groove bearings directly into a redesigned oversized shell. This was a big mistake, especially in hindsight when frames were made from carbon. The BB shell on an aluminium bike is a fragile, highly stressed component. It is a little thin-shell transverse tube with four major welds connecting it to the top tube, seat tube and two chainstays. This welding distorts the shell. This happened with old BBs as well but now with BB30, the bearing was fitted directly into the shell by press-fit. Tolerances had to be very high if you don't want the bearing to bind because of out-of-roundness of the shell and, simultaneously you want the bearing to fit tight enough into the aluminium shell to not move and fret during hard pedaling. This is an impossible call. These bearings all move and creak. The Japanese had some wisdom in using a screw-in system and sticking with it. Further, the bearings in BB30 are not far enough outboard to prevent the aluminium crank spindle to not flex and cause lateral loading of the bearing. That's why it fails so quickly.
BB30 became an even worse idea when frames turned to carbon. Now the BB shell was too soft to accept a steel bearing directly and, cannot be machined even close enough to good enough tolerance in anyway. Out came another shell redesign and we got BB30 Presssfit. This called for the bearing to be housed in a plastic cup which is then pressed into the imperfect frame aperture. They creak like hell and wear the shell out in an oval shape. They are terrible.
"And that's where we are today. Weight weenies, poor engineering and national pride gave us a system that is worse than the 50 year old (guessing here) square taper. No-one admits it, few mechanics understand it and they're all looking for solutions such as warrantee replacements bearing glue and hope.
"The answer will only be found once we have a new design. Don't think BB-Right provides it either."
to weight weenies!
