In March of 1978, the International Harvester Corporation started development of an engine that would eventually change the way pickup trucks and light-duty vehicles would be powered. The 420ci (6.9L), naturally aspirated (non-turbo), indirect-injected (IDI), diesel V-8 would find a home under the hood of Ford pickup trucks, and the diesel power culture would be born.
The Ford/IHC 6.9L engine featured a bore of 4.00 inches, a stroke of 4.18 inches, produced 170 hp and 310 lb-ft of torque with a 20.7:1 compression ratio. It may not sound like much by today's diesel standards, but 24 years ago it started a diesel revolution!
Engine Block
Made from cast iron, the 6.9L featured 4-bolt, nodular iron main bearing caps. This was done for reliability and also to increase the stiffness of the lower end of the block. In addition, typical of light-duty engines, bulkhead window core support holes were eliminated. This further increased stiffness and eliminated a potential area of failure.
IHC engineers used the then-new finite element analysis procedure to optimize performance. This study indicated that a significant reduction in deflection could be realized by increasing the bulkhead thickness in the area around the cam bore from 0.62 inch to 1.12 inches. This change was incorporated into the production engine.
The cylinder bores were not siamesed and were 0.26-inch thick. The five head bolt bosses per cylinder were not joined to the cylinder walls, but tied directly to the main bearing bulkheads through the outer water jacket walls or free-standing interior bosses. The design was used to minimize cylinder bore distortion during machining, assembly, and in operation. The front end of the engine block was extended to form a cavity for the geartrain and provided an ideal location for the fuel lift pump, thermostat, thermostat bypass, and water cross-over between the cylinder heads.
The 6.9L block also included many advantages in terms of flexible packaging for use in varied vehicles and to improve in-field service. The pan rail had tapped holes for oil pan mounting and were arranged for a reversible oil pan along with either a front or rear dipstick. The water inlet cavity provided flexibility for both size and location. Light-duty truck mid-engine mounting bosses and heavy-duty truck front-mounting bosses were included in the design. The engine block valley was cast open, and the roller valve tappets were serviceable without removing the cylinder heads.
A positive-displacement geardriven oil pump was located at the front of the first bearing cap and driven by the crankshaft gear. The pump was mounted to, and located by, the same machined surfaces as the bearing caps; doweled location holes were not required. Oil was routed via drilled passages throughout the crankcase. No external lubrication plumbing was required.
The injectors were placed...
The injectors were placed inboard along with the glow plugs.
Rotating Assembly
The crankshaft was designed to the same criteria that IHC applied to its heavy-duty line of diesel engines. For reliability, a forged steel material was chosen, which could be sufficiently strengthened. Through extensive testing, the operating stress levels were measured in the critical areas. From those measurements, the manufacturing process and heat-treatment requirements were established.
The crankshaft was forged from 15B28H steel and quench-and-tempered to a minimum hardness of 217 Brinell hardness number (BHN). The five main and four pin journal surfaces were induction-hardened to Rockwell hardness (RC) 50-55 for wear resistance and to allow in-service re-grinding. The pin fillets were induction-hardened to Rockwell hardness 50-55, then ground flush with the pin surface for fatigue life. The combination of processes and design provided a very strong crankshaft and a long service life.
External balance weights in the flywheel and a vibration dampener were required to keep the overall engine size within that of a gasoline engine and to limit the scrap rate during manufacturing.
The front and rear crankshaft oil seals were a one-piece design that were springloaded and featured trimmed flouroelastomer material. Both oil seals rode directly on the ground sealing surfaces-the front seal on the vibration dampener and the rear on the crankshaft rear flange.
The connecting rod and cap were forged from alloy steel as one part and cut into two pieces early in the machining process. In order to achieve adequate fatigue strength, the forging was heat-treated to obtain a surface hardness of Rc 27-33. This also provided adequate core hardness for surface strength of the critical stress areas. After heat treatment, the rough forging was shot-peened to provide a margin against flaws as well as undesirable residual stresses from operations such as straightening.
The small end of the rod used a steel-backed bronze bushing, which was pressed in place and bored to the final dimension. As was traditional IHC protocol, the rod design was proved acceptable by both static strain and fatigue tests prior to running in an engine.