The wheel cover on my S21ZSN will not stay against the rear wheel. With a lot of force you can make it snap into the wheel, but as soon as the wheel turns, the cover pops out except where the drive pinion washer holds it in. This makes the opposite side open about 1/4". I cleaned the areas where they meet carefully. I could put lubricant there, maybe WD-40. That would make it easier to push them together, but I'm think this would also make it easier for them to separate as soon as you turn the wheel. They don't seem to want to stay together, like they are slightly different sized. Has anyone ever seen this issue? Warpage from something? Does anyone have a couple of old covers I could get and compare to mine?
Update:
I put one of the wheels in my drill press and used my Dremel to 'machine' the inside diameter of the wheel larger by about 3/32" down about 1/4". Now the cover sits on the inner ridge with no problem, but the cover itself is about 1/8" from meeting the outer edge. Again, I can physically push that edge down into the wheel, easier now, but now it slides back out easier, too. Does anyone else have this type of mower? Doing a cross-reference, it looks like this system was used from 1986 to 1989 on models 8125, 8156, 8157, 8157A, 8157A1, 8440AE, S21BSN, S21ESN, and (my model) S21ZSN. Is the cover on yours flat? Mine curves inward toward the center, which is what pulls the outside rim out away from the wheel now.
