The Chevrolet 250 cubic-inch straight-six engine was used in Chevrolet, Pontiac, Buick, and Oldsmobile passenger cars from 1966 to 1979, and in light trucks until 1984. The 250 engine uses hydraulic lifters and stud-mounted rocker arms, similar to the small-block Chevrolet V8 engines. The hydraulic lifter system generally needs no adjustment, but if repairs have been performed on the engine, an initial adjustment would be necessary.
Use a ratchet and socket to remove the bolts from the valve cover. Remove the valve cover. Remove the gasket from the valve cover. Scrape any remaining gasket material from the valve cover with a putty knife. Place some shop rags on the cylinder head, next to the head's gasket surface. Scrape any gasket material from the cylinder head with the putty knife. Use the shop rags to prevent any debris from falling into the cylinder head.
Find the timing marker on the left side of the timing cover. Use a ratchet and socket on the large bolt in the center of the crankshaft pulley to rotate the engine in a clockwise direction until the notch in the crank pulley lines up with the "0" on the timing marker. Check to make sure that both valves on the number one cylinder are closed. If not, rotate the crankshaft another complete revolution.
Adjust the number one cylinder intake and exhaust valves by using a ratchet and socket to loosen the adjusting nut in the center of the rocker arm until there is play between the rocker arm and the end of the push rod. Slowly tighten the adjusting nut while spinning the push rod back and forth between your thumb and forefinger. When the push rod stops moving, slowly tighten the nut one additional turn. For 1976-77 engines, turn the adjusting nut 3/4 turn.
Adjust the following valves in the same manner: Intake number two and four. Exhaust number three and five.
Turn the crankshaft one complete turn. The number six cylinder valves should be closed. Adjust both valves in the same manner, then adjust the number three and five intake, and number two and four exhaust.
Spray a shop rag with parts cleaner and clean the gasket surfaces on the valve cover and cylinder head. Apply a coat of gasket sealer to one side of a new valve cover gasket and position the gasket on the valve cover. Coat the exposed surface of the gasket with gasket sealer and install the valve cover onto the cylinder head. Install and tighten the valve cover bolts.
