naavt wrote: ↑Wed Jan 31, 2024 11:01 am
I'm a very big fan of Campy in a country that nobody uses it, I have 4 bike equiped with Campy stuff... and the wavy washer on Campy cranks are probably the most idiotic piece of garbage that I've seen on a crank.
But again... that's only my opinion.
In this case a slightly misguided one.
The wavy washer is the method that Campagnolo's bearing supplier in co-operation with the designer of UltraTorque, settled on, to correctly apply a known axial pre-load to the bearing (which is one reason why "Rogue Bike Mechanic", mentioned elsewhere in this thread, has it wrong).
Provided that the BB cups are within +/-0.8mm of the nominal distance apart, the wave washer will take up the space & preload in the correct range specified by the bearing manufacturer.
The BB bearing works best with a preload because of the cyclically assymetric nature of the load across the bearing - not an uncommon situation in many crank arrangements (not restriced to bicycle, obviously) and some form of preload is used in many such bearing assemblies in part to counter it - the issue being that in these situations, the ballbearings on the "unloaded" side of the bearing will, if the whole assembly is not subject to a pre-load, "skate" on the bearing surface because their clearance will open up as the clearance closes down on the "loaded" side. This increases wear and shortens the life of the bearing assembly as a whole.
There is a good summary document that explains the principle of "negative clearance" in clear layman's terms here:
https://cdn.skfmediahub.skf.com/api/pub ... medium.pdf
If you want to argue with SKF, go right ahead. They are part of Schaeffler Group, who licence the use of Cronitect, a bearing material that plays a key part of the bearings that Campagnolo use for UT bearings.
The use of pre-load has some secondary advantages in compressing the bearing to provide greater functional rigidity in the assembly and to maintain the centre on the BB axle, as well.
None of this is secret or any part of Campagnolo IP, by the way. You can find the references for yourself but it's kind of bearing technology 101 ...
Re Rogue Bike Mechanic - He hasn't properly understood the principles ... RBM is relying on (in bearing terms, approximately) "filling the gap" to eliminate end-float but that approach has two problems.
First is shim thickness. When you are dealing with bearing clearances of 0.012-0.028mm (min & max value for c3 clearance on a 25m shaft size), a shim width of even 0.13mm doesn't cut it. I believe that is his minimum shim width. At the small end of c3 tolerance, that's a whole order of magnitude too great, to tune the gap-filling accurately enough. Even if he now has a thinner shim at 0.05mm, he's still out by a factor of between 2 and 5 and in addition to that, by stacking washers, you are stacking tolerance errors. They might even out, it's true. Then again, you might not. you won't know.
Second is that if the bore is over-packed with washers in an attempt to create preload, it's a complete guess as to whether the width of the shim is creating the right negative clearance, or too much, or not enough - but it's relatively unlikely to be right ... or even in the right range.
A Tech-Reps work is never done ...
Head Tech, Campagnolo main UK ASC
Pls contact via velotechcycling"at"aim"dot"com, not PM, for a quicker answer. Thanks!
