This sounds like a good start.
I forgot to ask, did this start just at random, or was it after a sharpening or blade change? You may have mentioned it but I didn't see it. If it's never happen before a change or removal then stands to reason something has obviously changed.
May try to hang torque the blade using a torque wrench and blade buddy or something to secure the blades while tightening, just to be 100% sure it's to spec. Torque wrenches can over torque fast.
We finally figured it out! You know we kept asking SEARS why they were selling us star blades when the spindle screw was round an they kept saying that is just the way it was. We questioned why there wasn't a star bolt to put the star blade. Well, come to find out they were totally wrong. What was happening was as the blade spun around and around the round screw part of the spindle would start wearing down the insides of the star which gave it leeway to shift back and forth and this particular blade that kept shearing would be able to move enough to start catching the inside of the metal opening where the cut grass went out. It would keep hitting and hitting til a slither on the blade produced would completely catch the metal and STOP the blade, with the spindle still spinning 90mph it would shear. When we took the other blade off on the other side, the inside of the "star" was completely worn smooth giving it room to move too, only there wasn't an opening for the blade to catch like there was on the other side. When we went to sear again to buy blades, we took the book with us, the blades they brought us were not the same number and we showed them, they said, they will work, they are the same size. We said NO we want the ones with same PART NUMBER as shown in the book. They went back and brought us blades with the same PART NUMBER. Guess what, they were NOT STAR blades!!! Simple as that.... $600 in repair parts later. We have been mowing for a week straight and no problem. We had just bought this mower from my brother and knew he had never had problems with it before. We talked to him and he mentioned that when we bought it, the day before we picked it up, he went to Sears and bought a new belt and blades and replaced them so they would be new when we picked it up. Trying to be nice (smile). Sears sold him the "star" blades. Anyways, thanks for all your help! If this ever comes up again, just be adament with Dealers... you don't put a "star" blade on a "round" spindle. I don't care how many times they say "that is how they are constructed."
