Chevrolet Blazer/Jimmy 1969-1982 Repair Guide

Design

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GASOLINE ENGINE



All Blazer and Jimmy engines are water-cooled, overhead valve powerplants, using cast iron cylinder blocks and heads.

The 250 cu in., inline six cylinder engine crankshaft has seven main bearings, with the thrust taken by No. 7. This results in a very rigid crankshaft assembly. The camshaft is low in the block and driven by gears rather than the usual chains and sprockets. Fairly long pushrods actuate the valves through ball-mounted rocker arms. This engine has changed very little over the years, giving a great interchangeability of parts. A major change was introduced in 1975. This is an integral cylinder head and intake manifold casting. The integral design results in better emission control and more power and economy.

The small-block family of V8 engines, 305-307-350 and 400 cu in. engines, are all derived from the innovative design of the original 1955 265 cu in. Chevrolet V8. This engine introduced the ball-mounted rocker arm design, replacing the once-standard shaft mounted rocker arms. There is extensive interchangeability of components among these engines, extending to the several other small-block displacement sizes available in passenger cars. The 400 cu in. version differs in block design; it does not have cooling passages between the cylinders, as on the smaller V8s.

Don't confuse the Blazer/Jimmy 400 with the big-block engine used in passenger cars, identified variously as 396, 400, or 402 cu in. The small-block engine can quickly be identified by the placement of the distributor at the rear.

DIESEL ENGINE



The 6.2 liter, 379 cu in. V8, 4 cycle diesel engine is developed and produced by Chevrolet. It is a totally new engine designed specifically for truck application with heavy duty usage in mind.

The base of the engine (short block) is very similar in design to a V8 gasoline engine; the major difference being the cylinder heads, combustion chamber, fuel distribution system, air intake manifold and the method of ignition. The cylinder block, crankshaft, main bearings, connecting rods and pistons look much the same as their gasoline engine counterparts, although they are of much heavier construction due to the higher compression ratio required to ignite diesel fuel. The intake and exhaust manifolds are of special design and construction.

The cylinder head incorporates a 17 bolt head design which locates 5 bolts around each cylinder. This helps gasket durability. It also includes a high swirl pre-combustion chamber which mixes fuel and air to provide an efficient fuel burn and low emissions. A special cavity in the piston top further assists in mixing the combustion products for complete burning.

Main bearing caps all use 4 bolts instead of the normal 2 to provide rigid support for the crankshaft and minimize stress. The rolled fillet nodular iron crankshaft utilizes a torsional damper, tuned to reduce vibrations.

The engine also uses 3 roller hydraulic lifters running on a forged steel camshaft.

 
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