I'm just about to make the pistons for my 5-cylinder radial. The plans call for a cylindrical profile, the bottom skirt portion is shelled out and a further deeper milled slot for the link rod. I noticed the Edwards radial is much the same. But I've noticed almost every RC 4-stroke engine I've examined (and the odd hobby designed engine) has a further scallop or milled reduction in the skirt like the OS-56 piston on the left. I don't think its for any kind of clearance & I doubt the weight reduction is of consequence. So wondering if its to provide more direct flow access to mist lubrication. Any thoughts?
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