Knife Edging the counterweights on the crankshaft is essential for two main reasons. Firstly, knife edging the counterweights enables them to pass through thick oil mist within the crank case more efficiently. Think of knife edging as a form of aerodynamics for the crankshaft, reducing drag caused by air and mist within the crank case. This helps the engine rev more freely and easily. Secondly, knife edging is subseqeuntly also a form of weight saving, removing material from the counterweights of the crankshaft.