A few posts about the humble retaining ring. There was a broken one laying at the bottom of the engine when I took it apart. It was used to retain a spinning or sliding component on a shaft. An external retaining ring fits in a groove around a shaft and it was one of those that let go.
Right now I am looking at the broken ring. Where it came from is immaterial at this time. The goal is to look at the ring and read its story. Its condition will tell me a lot.
First, I look for wear. A worn ring that has lost a lot of metal is weak and easy to dislodge or break. The ring to the right in the first picture has lost a lot of metal. It was replaced during a periodic inspection before it failed. My broken ring has very little wear. This is not the failure cause.
Second, I look for discoloration or signs of heat. Is the ring annealed by heat and easy to bend? An overheated ring that has lost its temper is weak and easily dislodged. My broken ring does not show signs of overheating.
Third, I look for distortion such as necking near the break or bending. This would indicate a sudden load stretched the ring through elastic and plastic deformation until it finally was pulled apart. The parts of my ring are not bent or stretched. There is no necking near the break. Nothing indicates it was pulled apart.
Fourth, was the ring put on the shaft backwards? These rings are stamped from steel plate. There is a face with a rounded edge and the other face has a sharp and square edge. The loads on the ring should push the sharp edge toward the side of the groove on the shaft. The wear marks tell the story. The wear mark on the sharp face should be at the inside edge of the ring. This is the reaction wear mark. The ring to the left in the first picture shows a wear mark on the inside of the sharp face, like it should. The second picture shows the rounded sides of two rings. The wear marks are on the high points in the middle of the rings. These are from the spinning gears and they are the load wear marks. The loads are being applied to the correct faces on these two examples. My broken ring was installed correctly.
Fifth, the process of elimination indicates that my ring was not worn out, broken from some sort of massive load, overheated, or installed backwards. Metal fatigue from a cyclic load was the failure cause. The engine shafts and other parts will be examined in the next post.