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crankshaft machining drill crankpin journal plug oil passage drilled between the 2 holes this is an example of a one-piece bolt up crankshaft note the hole drilled in the crankjournal and the crank pin journal crank webs crankjournal oil is pumped from the oil pump through passages in the crankcase to the crank journal main bearings a hole is drilled through the crank journal and the crank pin journal another passage is drilled down through the crank web connecting the two holes the passage is then plugged where it was drilled on the web this creates a passage between the crank journal and the crank pin journal where lubricating oil can flow the oil is pumped to the crank journal then through the oil passage in the crankshaft to the crank pin journal in this way both bearings are effectively lubricated twin cylinder crankshaft plug oil passage oil passage plug each crankshaft journal lubricates a crankpin journal except for the middle crank journal in this case