Join Date: Apr 2006
Location: minnetonka , mn, usa
Re: A K1200RS FD failure
Curtis - I had not seen that posting. Interesting how much discrepancy between the BMW Book recommendation & the actual, and how your method came out the same as the recommended method. That bearing is so much toast that there probably isn't anything to be learned from it.
I've been trying to think of a way that the axial deflection of the hub could be measured under a thrust load. The thrust could be applied by a fixture supporting the case, & using a non-rotating drill press & a torque wrench on the drill press handle. The deflection could be measured with a dial indicator & an appropriate zero stress fixture to hold the dial indicator with respect to the housing. Sort of like you have now.
I would expect that the line of contact between the races and the balls shifts quite radically as the preload force is applied. Too low a preload = lot of deflection, & very little preload = not much deflection. It might make a way that the preload could be approximated on an assembled unit. This would allow a more direct measurement of preload than the present assembly method which is probably sensitive to things such as shaft diameters etc.
It would be necessary to both push as well as pull on the hub measuring hub-to-housing deflection. I would expect a force of maybe 500 lbs would be necessary.
Of course the tapered roller bearing would also enter into any deflection vs load measurement, but I suspect the line-of-action of the tapered roller bearing remains very consistent.