Caterpillar 3406

The Caterpillar 3406 is a heavy-duty, inline six-cylinder, four-stroke diesel engine displacing 14.6 L (893 cu in), built from a 137 mm (5.4 in) bore and 165 mm (6.5 in) stroke. Caterpillar introduced it in 1973 as a new mechanically governed design rather than a direct replacement for an earlier Cat engine, and offered it in naturally aspirated, turbocharged, and turbocharged-aftercooled configurations; on-highway ratings ran roughly 255-425 hp (190-317 kW) with torque up to about 1,460 lb-ft (1,979 Nm), while industrial, pump, marine, and generator-set ratings could run higher, so exact figures vary by configuration and series. Dry weight varies the same way, from roughly 1,490 kg (3,300 lb) as a bare long block to around 3,100 kg (6,800 lb) fully dressed for truck or industrial mounting. Caterpillar built this original mechanical-injection engine into the mid-1980s, when the 3406B took over (this early version is often referred to afterward as the 3406A), and used it across on-highway Class 8 trucks, off-highway haul trucks and scrapers, marine propulsion and generator sets, and stationary industrial power units.

Across the 3406 family, the fuel system marks each generation: the original 3406 and the 3406B ran purely mechanical, camshaft-driven unit injectors with a flyweight governor; the 3406C added Caterpillar's PEEC electronic governor on top of that mechanical injection hardware; and the 3406E went fully electronic with Cat's own electronic unit injectors. That mechanical simplicity is why the base 3406 still has a following in the rebuild and used-parts market: no ECM and no injector wiring harness to fail, which suits marine, generator-set, and industrial operators who want a diesel a shop can service with hand tools and a timing gauge. Cylinder block, head, and rotating-assembly architecture carried forward largely unchanged into the 3406B, so cores, machining practices, and reman knowledge built around this original engine still support the broader 3400-series parts supply chain today.

Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.