A few years ago, because it was on sale not that I needed it, I picked up a knuckle cap block plane. I'd never used a knuckle cap plane so I hadn't a clue how it should work. Bottom line on this plane: If the cap was loose enough to move the iron the cap would snap open at the slightest touch. the only way to keep it closed was to go Bubba on the screw and have it too tight to move the iron. That combined with adjustment problems caused me to just put it on the back shelf and basically forget about it.
A couple of days ago while waiting for the paint on the CDFH (cabinet doors from hell) to dry I was doing some tool maintenance. I spotted the knuckle cap block plane setting all dusty on the shelf and decided to give it a go. I pulled it apart and did a good sharpening of the iron and inspected the base. Every thing looked OK except the grinding of the bed looked a little different left to right, not much but just a little. I put the iron back in Bubba'ed the knuckle cap down and tried a shaving. Same story, heavy shaving on one side nothing on the other. I slewed the iron as much as possible, same story. Shavings on the left side nothing on the right. Resharpened the iron and checked for square, checked the mouth for square, checked the bed for junk on the bed, all OK but still the same story. The wood store was still open so I put everything together and off to the wood store. Once there we all stood around scratching our respective butts until one of the younger guys that could still see held the body just right to reflect light off the mouth. You could see the light line was much thicker on the right side than the left. They replaced the body with one from stock.
Once home I put it to some wood, with the knuckle cap tight enough to hold but loose enough to adjust the iron like it should be and the little plane works like a champ.
I'm not sure there is a point to the story other than pay attention to what the tool is trying to tell you. The knuckle cap was screaming "this tool is defective" and I was too dumb to hear. I will know better until the next time.
ken