What component supports the crankshaft inside the crankcase?

• A. Main bearings within the crankcase.
• B. Piston rings.
• C. Timing gears.
• D. Valve springs.

Answer: (A)

The main concept here is how the crankshaft is held in place and allowed to rotate inside the crankcase. The crankshaft is supported by main bearings (journal bearings) located in the crankcase. These bearings provide a smooth, low-friction surface for the crankshaft journals to rotate on and carry the radial loads from the rotating crank and connected components. They also help keep the crankshaft properly aligned and handle thrust forces as the pistons push and pull.

Piston rings seal the piston to the cylinder wall and help contain combustion pressure and oil control; they don’t support the crankshaft. Timing gears drive the camshaft (for valve timing) or timing chains, but their role is not to support the crankshaft. Valve springs are part of the valve train and also do not support the crankshaft.