This Operation and Maintenance Manual covers Caterpillar 3304B and 3306B diesel engines. These engines are known for their robust construction and reliable performance in various demanding applications. The 3304B features a displacement of 6.6 Liters, while the 3306B offers a larger 10.3 Liter displacement, providing power and efficiency for diverse operational needs. Their liquid-cooled systems ensure consistent operation under heavy loads. This manual provides comprehensive guidance for the repair, maintenance, rebuild, refurbish, and restoration of these engines. It includes detailed procedures for diagnostics, troubleshooting, and covers electrical systems with included wiring diagrams. With numbered substeps, detailed steps, and enhanced illustrations featuring bold figure numbers, drawings, photos, and inset views, this English-language manual is designed to assist owners, mechanics, and technicians in effectively maintaining and repairing their Caterpillar 3304B and 3306B engines.