GM Full-Size Trucks 1970-1979 Repair Guide



All Chevrolet and GMC truck engines, whether 6-cylinder or V8, are water-cooled, overhead valve powerplants. All engines use cast iron cylinder blocks and heads.

The 6-250 and 6-292 inline engines are all very similar in design although some 6-250s have an integral cylinder head and intake manifold beginning 1975. Crankshafts are supported in seven main bearings, with the thrust taken by No. 7. The camshaft is low in the block and driven by the crankshaft gear; no timing chain is used. Relatively long pushrods actuate the valve through ball jointed rocker arms.

The small block family of engines, which includes the 8-283, 8-305, 8-307, 8-327, 8-350, and 8-400 blocks, have all sprung from the basic design of the 1955 265 cu in. engine. It was this engine that introduced the ball joint rocker arm design which is now used by many car makers. This line of engines features a great deal of interchangeability, and later parts may be utilized on earlier engines for increased reliability and/or performance.

The Chevrolet built V6 262 cu. in. engine introduced in 1986 evolved from the small block V8 family of engines and share many of the same parts.

The 8-396, 8-402, and 8-454 engines are known as the Mark IV engines or big blocks. These engines feature unusual cylinder heads, in that the intake and exhaust valves are canted at the angle at which their respective port enters the cylinder. The big block cylinder heads use ball joint rockers similar to those on the small block engines.

Two V8 diesel engines have been available in the Chevrolet pick-ups since 1978. The first was the Oldsmobile built 8-350 engine which was derived from a gasoline engine of the same displacement. Internal engine components such as the crankshaft, main bearings, connecting rods, pistons, writs pins and piston rings all are heavier made to withstand the considerably higher pressures and stresses common to diesel engines.

Diesel ignition occurs because of heat developed in the combustion chamber during compression. This is the reason for the diesel's high compression ratio (22.5:1). Because the fuel ignites under compression, the need for spark plugs and high voltage ignition is eliminated.