I have a 34" Gravely walkbehind. This morning I took off the blades to sharpen them, and had a lot of trouble putting them back on. I do remember I had an accident last season that could have slightly messed up the thread on the inside of the spindle, but I've sharpened the blades several times since then and put the blades back on with no problem. But this time, it becomes impossible to screw in the bolt more than 1/3 of the way, and when I use a wrench, the bolt simply drops back down a little after it reaches a certain point. I have no idea how this happened. Anyway, is there anything I can do to fix this? I'd rather not buy a new spindle assembly ($$$) and I can't really put any more washers on it - the blades will only be hanging on by maybe 1/4 inch of the bolt.