Caterpillar 3304

The Caterpillar 3304 is an inline four-cylinder, four-stroke direct-injection diesel engine with a displacement of 7.0 L (425 cu in), a bore of 121 mm (4.75 in), and a stroke of 152 mm (6.0 in). It is the four-cylinder member of Caterpillar's 3300-series engine family, which traces its lineage directly to the earlier D330 and D333 engines of the 1960s — the 3304 can be understood as a D333C with a revised designation and refined fuel system. Production began in the early 1970s alongside the six-cylinder 3306 (the 3304 shares the same bore, stroke, block architecture, and wet-sleeve liner system as the 3306 but with two fewer cylinders). The engine was offered in three principal configurations: naturally aspirated (NA), turbocharged (T), and turbocharged with direct injection (DIT/DITA); an earlier precombustion chamber (PC) head design was used until approximately 1979, after which direct injection became standard across the range. Depending on configuration and application, gross power outputs range from roughly 47 kW (63 hp) for the base naturally aspirated version to over 103 kW (138 hp) for the turbocharged DIT marine and industrial variants. The engine powered a broad spectrum of Caterpillar machines including the 920, 930, 950, and 966C wheel loaders; the D4D, D4E, and D5B track-type tractors; the 112, 120, and 120G motor graders; the 931, 933, 951, 955, and 977 track loaders; early 225 excavators; plus numerous generator sets, marine propulsion, and stationary industrial installations. Dry weight varies by configuration from approximately 726 kg (1,600 lb) to 816 kg (1,800 lb).

The 3304 evolved meaningfully across its production life. The earliest engines used a precombustion chamber (PC) head paired with a scroll-type injection pump; this combination delivered acceptable low-speed torque but limited peak output and fuel efficiency. From around 1979 onward, Caterpillar transitioned to a direct-injection combustion system with a revised scroll pump — an update that improved thermal efficiency, raised power ceilings, and reduced fuel consumption per kilowatt-hour. Turbocharged and turbocharged-aftercooled (DITA) variants further expanded the power band for high-demand applications such as marine propulsion and large generator sets, where the engine could reach outputs approaching 165 hp. The 3304B designation, which appeared in some marine and generator-set specifications, represents a further iteration with additional refinements — it is a closely related but distinct variant and should not have its performance data conflated with the standard 3304. Production wound down through the 1980s and into the 1990s as Caterpillar migrated to the 3300B family and, eventually, to electronically controlled engines and the modern C4.4 platform to meet successive emissions regulations. In the used and rebuilder market today, the 3304 commands strong demand precisely because of what it is not: there is no electronic control module, no emissions aftertreatment, and no proprietary software required to service it. Rebuild kits remain widely available from multiple suppliers, in-frame overhauls are straightforward, and the engine's gray-iron block and ductile-iron wet-sleeve liner design is inherently rebuildable to factory tolerances with common machine-shop tooling. For operators running older Cat fleets in remote locations or emissions-exempt applications, the 3304 represents one of the most economically serviceable diesel engines ever produced by the company.

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