I agree with you, ‘Production tolerance variations could be significant.’ A collection of tolerances on one side of the range could be expressed one way on this bike and another bikes ‘DNA’ not expressed at all. It helps explain the different range of experience members have. There is also personal perception, fingernails on the black board makes me cringe. For another it could be just background noise.
I have kept that bellville washer on the hub. It is an active separation feature. As I think I mentioned somewhere, the difference between the unsprung bellville washer and it’s washer and the friction plate height is very close, I won’t say exact anymore, to the .125mm for each space. When the pressure plate is disengaged, this first plate, at the hub, has to wait its turn to separate. That bellville washer gives a little push to the rest of the plates. I have wondered about a clutch where each pair of plates had a bellville washer. Little dictators, nothing to see move along. I agree more space on the hub for the plates to shift would be where I would start.
I have to think those that designed this clutch had something in mind. The characteristics they were after resulted in some trade offs. This is pure speculation, this bike was designed to be fast through the gears. 2.8 seconds! Is the small amount the clutch lever has to be pulled to initiate a gear change, one of those trade offs? Speed over clunk.
I initially spent weeks trying different ways to add oil. Lack of oil has been the gold standard. I could not change the clunk in any way by trying to increase the oil. This embedded idea of not enough oil I think comes from the wear seen on the hub and pressure plate. I’m starting to think that the ‘clunk’ itself adds to the wear. This rotating mass comes to a sudden stop. Seems there is some sliding of the plates under pressure until they break. One of Patrique Hofmann’s early videos shows the clutch he has removed from his bike. The whole thing was bone dry. The hub and first plate as well as the friction against the pressure plate were worn bare. But all the middle plates looked fine. He remarks that he is surprised it didn’t blow up. There were a few issues with oil nozzle and oil holes. For me this pointed to where the amount of oil was important. The middle of the clutch pack needed just enough oil that it’s shear strength is easily overcome. (Shear strength, that was the word I was looking for. Fluid coupling as a term is more all encompassing. Shear strength is more specific.). At the hub and at the pressure plate is where oil is the most critical.