crankcase

The crankcase is the housing that encloses the crankshaft and related components of an internal combustion engine. It forms part of the engine block and provides a sealed enclosure for the crank mechanism, bearings, and often the oil reservoir. In most engines, the crankcase also serves as the sump for lubricating oil and includes passages for oil circulation and cooling.

The crankcase typically comprises the main body, the bottom oil pan or sump, and, in many designs, a separate upper cover or cylinder block that closes the engine. It may be a single piece or two halves bolted together. The crankshaft, main bearings, and connecting rods reside inside, and the timing geartrain or chain is often located in the upper portion.

Lubrication is a primary function: oil is pumped through galleries to bearings and moving parts, then returns to the sump. Modern engines use a crankcase ventilation system (PCV) to remove blow-by gases and maintain pressure balance.

Materials and construction vary; common materials include cast iron and aluminum alloys. Designers emphasize stiffness to reduce flex while controlling weight and oil pressure. Some engines use a dry-sump system with an external reservoir and scavenging pumps; most use a wet-sump oil pan.

Maintenance and issues: oil leaks from gaskets and seals, sludge buildup, and crankcase pressure from restricted ventilation can occur. Regular oil changes and inspection of seals help prevent problems.