GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide



All Buick, Olds and Pontiac engines covered in this guide, whether V6 or V8, are watercooled powerplants with pushrod valve actuation. All engines use cast iron cylinder blocks and heads.

The gasoline V8s are all very similar in construction and share common design features such as chain-driven camshafts, hydraulic valve lifters and pressed-steel rocker arms. The Oldsmobile 307 cu. in. (VIN Y) engine uses roller valve lifters after 1985. The Buick engines, including V6s, differ in that they have their rockers mounted on shafts. Because of this similarity between the engines, many removal and installation procedures given here will simultaneously cover all three manufacturers' engines. Likewise, the 231 and 252 V6 engines are nearly identical to each other and to the Buick V8s.

The 350 diesel is derived from the 350 cu. in. gasoline engine, but virtually all major engine parts were strengthened to withstand the higher compression ratio and combustion pressures. Fairly early in the production run the standard valve lifters were replaced with roller type hydraulic lifters because the particles generated in diesel combustion were causing camshaft and lifter wear problems. The diesel engine cylinder head design is different from the gasoline engine design, in that the diesel incorporates a special steel insert that forms a precombustion chamber and must be properly fitted to ensure proper operation.

One especially important difference in the diesel relates to the high compression ratio. The area between the piston top surface and the lower surface of the cylinder head is very small and there is minimal clearance between the piston and valves. For this reason, any engine work related to the valves, lifters and intake manifold requires particular attention to special diesel service procedures. Failure to follow these procedures will often result in bent valves or valve gear.

The diesel fuel system is considerably more complex than the typical gasoline engine carburetor. Particular attention must be paid to fuel cleanliness and maintenance of various fuel filters and water separators. Service on this system usually requires extensive specialized tooling and training. It should never be tampered with, as this can result in personal injury. Make sure you are properly equipped and fully aware of proper service procedures before you begin work on it.