Machining oval cores in crankshafts

A method of manufacturing a crankshaft assembly, the method comprising:

• forging a crankshaft having a pin bearing journal, a main bearing journal, a first crank arm supporting the pin bearing journal, and a second crank arm supporting the pin bearing journal and connecting the pin bearing journal and the main bearing journal;
• drilling or milling at least one crank arm cavity within at least a portion of the second crank arm, the at least one crank arm cavity being accessible for the drilling or milling only when a removable counterweight is removed;
• coupling the removable counterweight to the first crank arm after the drilling or milling of the at least one crank arm cavity to form the crankshaft assembly;
• and
• drilling or milling at least one pin bearing cavity having a first cavity section, a second cavity section, and an enlarged central cavity section, the first cavity section extending substantially through the first crank arm, the second cavity section extending substantially through the second crank arm, and the enlarged central section extending through the pin bearing journal between the first cavity section and the second cavity section, the enlarged central cavity section being sized larger than the first cavity section and the second cavity section to minimize a cross sectional thickness between a radially inner surface of the central cavity and a bearing surface of the pin bearing journal.

A method of manufacturing a crankshaft assembly, the method comprising:

• forging a crankshaft having a pin bearing journal, a main bearing journal, a first crank arm supporting the pin bearing journal, and a second crank arm supporting the pin bearing journal and connecting the pin bearing journal and the main bearing journal;
• drilling or milling at least one crank arm cavity within at least a portion of the second crank arm, the at least one crank arm cavity being accessible for the drilling or milling only when a removable counterweight is removed;
• coupling the removable counterweight to the first crank arm after the drilling or milling of the at least one crank arm cavity to form the crankshaft assembly;
• and
• wherein the drilling or milling at least one crank arm cavity comprises a first step of milling, cutting, or machining a first portion of the crank arm cavity using a core drill and a second step of milling an uncut portion of the crank arm cavity using a mill cutter.