What is the function of the main journals?

• A. Serve as the points of support and as the center of rotation
• B. Provide lubrication to the crankcase
• C. Absorb heat from the crankshaft
• D. Drive the timing gears

Answer: (A)

Main journals are the bearing surfaces machined on the crankshaft that sit in the engine block’s main bearings. They provide the points of support for the crankshaft and define its rotation axis. As the engine runs, the radial loads from the pistons and connecting rods are carried by these journals through the main bearings, keeping the crankshaft aligned while it spins. A thin oil film between the journal surfaces and the bearings reduces friction and wear, allowing smooth rotation. The lubrication and cooling systems work around these surfaces, but the journals’ job is to support and enable rotation, not to drive timing gears or to supply lubrication directly.