Zderf and company:
Following my earlier post, I came home and finished drilling the safety wire holes in the tangs of the stainless steel replacement spinners and installed them. When I removed the old aluminum spinners, two of the four are now showing pitting and galling over a narrow (approximately 1/16 inch wide) band around the entire circumference of the beveled mating surface. The other two are showing similar galling over about 1/2 of the circumference. The galling is located at the outboard edge of the bevel, just below the tangs. All four exhibit a similar pattern, varying only in the length of the pitting. As a result, I consider the old spinners to be unusable. In my defense, I'll state that I have never overtorqued them during installation. I usually seat the spinners with a couple of light taps to each tang with a dead-blow hammer, lower the car to the ground and give each tang a good whack with the same hammer. I then safety-wire the spinners to the wheel spokes before driving the car.
As I stated in my earlier thread, I've talked with several folks who are far more educated in metallurgy than I, and all have said that mating aluminum to aluminum as in this installation will eventually result in this type of reaction between the pieces. Based on the particular pattern I saw on my spinners, it may well be that the angle of the mating surface of the spinner does not match exactly with the angle of the mating surface of the wheel, resulting in a stress concentration along the narrow band which ultimately seized up. If this is the case, seemingly normal tightening torque would result in excessive pressure at the points of contact between the two mating surfaces, and this would certainly contribute to the galling/seizing which I have experienced. Perhaps some sort of test with plasti-gage, such as used for the engine main bearings, would be able to tell; but at this point, I figured I was better off just replacing the aluminum spinners with stainless steel ones. I'm hoping that will resolve the problem permanently. Besides, the car was obviously feeling neglected since I haven't spent any money on it in a couple of months.
