— PART 1 —
For the SHIMANO Hollowtech II solution, you will need to first decide on which bearings you want as there are two options, (1) an $85 set of steel bearings or (2) a $195 set of hybrid-ceramic bearings. Currently, all Hollowtech II solutions come with 2437 bearings sourced from different suppliers. No industry standard 6805 bearings are available from Praxis and if you choose to swap out the 2437 bearings for the 6805 bearings, you WILL void the warranty.
DISCUSSIONS WITH MANY
“It turns out that the first 6 words in the question above
are the critical key to ultimately arriving at the answer.”
INTERFERENCE FIT or PLASTIC SHIM?
(metal-to-metal contact) is best, BUT,
that it also depends upon the application.
SO WHAT’S THE BEST SOLUTION?
(for an in-depth analysis [From Slocum A.H., Precision Machine Design, Prentice Hall, Englewood Cliffs, New Jersey 1992, pp 387-399], see excerpt from Professor Slocum’s book and class notes at the end of this review)
- PLASTIC REDUCER SHIM/DUST COVER (Shimano solution)
- Can build to slightly looser tolerance since the plastic shim will ‘take up the slack’
- Inexpensive piece that protects the crank spindle and bearings
- No mechanical difference when compared to metal-to-metal contact
- Eliminates virtually all squeaking between crank spindle and bearing
- Some aftermarket replacement plastic shims are made from a cheap brittle plastic and will crack when being reinserted into a bearing
- METAL-TO-METAL CONTACT
- A very reliable and rigid connection when done correctly, but also with the correct application
- The key phrase is “when done correctly.” Even though you will get a very reliable and rigid connection – after heating up the bearing and cooling the crank spindle, you would never be able to remove the crank in a bicycle bottom bracket application
- If BB bearing seizes, friction with metal-on-metal contact, while continuing to pedal, will overheat the crank spindle destroying its heat treating, and possibly ruin the crank – I’ve seen this on a customers bike
- Increased manufacturing time (i.e., increased cost) is needed to guarantee a precision interface, but still needs to be a looser fit between the bearing and crank spindle interface
- To prevent too high of a stress, the typical interference needs to be fairly small, nullifying most of the advantages of this solution. Problems include;
- Radial or circumferential stresses
- Buckling while pressing crank spindle into the bearing
- Clearance of the bearing can be exceeded forcing the balls to jam into the races
- If interface between crank spindle and bearing fit is too loose, crank might feel like it is wobbling or slipping
PART 1 SUMMARY