The 6-71 is a two-stroke engine.[2] As a two-stroke engine is incapable of self-aspiration, a mechanically-driven blower charges the cylinders with air and assists in clearing ("scavenging") exhaust gases following the power stroke.[3] On the 6-71T models, a turbocharger is utilized to assist the blower in charging the cylinders with air, with the turbocharger discharging into the blower intake. Unlike the turbocharger of a four-stroke engine, the primary purpose of the 6-71T's turbo is to reduce the blower's parasitic loading at higher engine power levels, which improves fuel economy.[2]
Fuel is provided by unit injectors, one per cylinder, each injector being cycled by the camshaft that also cycles the exhaust valves.[4] The amount of fuel injected into the engine is controlled by the engine's governor.[1] The engine cooling is via liquid in a water jacket. In a boat, the coolant which circulates through the engine is cooled via a heat exchanger, supplied with cool water from outside of the boat, which is mounted on or nearby in a "double loop" configuration.[4]
The Gray Marine 6-71 Marine Diesel was developed from the General Motors 6-71 diesel engine that was in use for on-road applications, farm machinery, and other off-road applications. Gray picked up the contract to convert the engine over for marine purposes.[5]
Use
The 6-71 was used for Higgins LCVP, a landing craft used in larger numbers during World War II.[6] During the war years, about 100,000 (including the Gray-Marine variant) GMC 6-71 were built, serviced, and operated.[3]