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Notice on the rear wall the plate "NO RUF" ! This is great....quite a project, you definitely need lots of expertise to build an engine like that. It would be great if you can post more pictures of the engine build !
Somebody else can probably provide a better response, but I think it has to do with reducing windage which is the negative work created when the crank moves through oil. By knife edging less work is required for the crank to do this work and hence better efficiency/increased hp. In addition, the crank weighs less also reducing rolling mass...however, I'm not an expert...
Yup, it primarily comes down to windage. You can also moon-cut the bottom of the barrels so that reduces the air flow when the piston comes down the barrel.