One winter I put the Atlas away after using all summer. When I brought it out next summer and started it up one piston began to make a lot of racket especially while warming up. As the days went by it increased so I fanally had to pull the cylinders off. One piston was noticably worn. So now I am running into the same problem with an A65. The motor was rebuilt by a reputable shop about a year ago and ran well. This year it has developed the familiar harsh whacking sound. How does this happen all of a sudden?