This manual covers the Caterpillar 3304 industrial engine, a robust and reliable diesel engine designed for a wide range of demanding applications. Known for its engineering quality and durability, the 3304 features an inline 4-cylinder configuration with a displacement of 6.6 liters. Depending on its specific configuration, this engine can be naturally aspirated or turbocharged, offering power outputs typically ranging from 90 to 150 horsepower. Its liquid-cooled system ensures consistent performance under various operating conditions, making it a trusted power source for heavy-duty equipment. This comprehensive English-language parts manual provides essential information for identifying, maintaining, and understanding the Caterpillar 3304 engine. It details various engine components, including the crankshaft, pistons, fuel system, electrical system, and cooling system, supported by detailed illustrations and drawings. The manual also outlines lubrication specifications, such as oil type and capacity, and provides guidance on maintenance intervals for oil and filter changes. Its structured format, including a table of contents and detailed repair procedures with numbered steps, is designed to assist owners, mechanics, and technicians in efficiently managing and servicing this industrial engine.