On the way home from the Scottish Austin 7 rally many years ago my wife was driving the Ruby when it started to lose power. I checked and found no 2 cylinder was not firing. As we were only 10 miles from home she just nursed it home. I had a rebuilt engine for it just changed them over and stuck the old one in the shed. I took it apart today and the pictures show what I found. The car still ran totally quiet and the lower half of the piston went up and down as normal.
This sort of failure with that style of piston was not uncommon on other makes but the area of metal to finally fail was usually very small. Did a bearing run or cap loosen and allow the top ring to catch? Can also follow a cracked crown but evidence of blow by through the crack then usually evident.
Charlie
You talk about a new piston, but how about a used one to match the others? I have a considerable collection of pistons, one of which might match the others. Send a PM if the idea appeals to you.
When pistons fail from some fatigue process all usually ishow fatigue similary progressed. I would expect the larger area to be the fatigue crack but it usually dull.
