351W Torque Specificationsby John Stevens J.D.
As with all engines, it is vitally important to follow the 351's torque specifications carefully to avoid damaging the engine block and the various components. The 351 falls within three engine designations, the W, the C and the M. The engines feature the same displacement but share little else in common. For this reason, it is imperative that the torque specifications for one engine not be used for a different engine designation. Also note that some torque specifications vary by the year of the engine.
Main and Rod Bearing Caps
Install the main bearing caps before installing the connecting rod caps. Tighten the main bearing cap bolts to between 95 and 105 foot-pounds of torque and the connecting rod cap bolts to between 40 and 45 foot-pounds of torque.
Cylinder Head Bolts and Rocker Arm Nuts
To avoid damaging the gasket, it is important to tighten all of the cylinder head bolts in small increments at a time until the final torque setting is reached. The torque specification of the head bolts varies depending on the year. Tighten the cylinder head bolts to between 95 and 100 foot-pounds of torque if the engine was manufactured for the 1969 through 1972 model years. Tighten the bolts to between 105 and 112 foot-pounds of torque if the engine was manufactured during the 1973 or 1974 model years. Tighten the bolts to between 95 and 105 foot-pounds of torque for the 1975 and 1976 model years. Unlike the cylinder head bolts, the rocker arm nuts may be tightened to their final torque specification individually. Note that the rocker arm specification also varies depending on the year of the engine. Tighten the rocker arm nuts to between 17 and 23 foot-pounds of torque if the engine was manufactured for the 1969 through the 1974 model years, and to between 18 and 25 foot-pounds of torque for the 1975 and 1976 model years.
Exhaust and Intake Manifold Bolts
Tighten the bolts on the ends of the exhaust manifold first and work inward. Tighten the exhaust manifold bolts to between 18 and 24 foot-pounds of torque. The intake manifold bolts should be tightened in a crisscross pattern to ensure even gasket sealing. Tighten the intake manifold bolts to between 23 and 25 foot-pounds of torque for all model years except 1975 and 1976. Note that the 351s produced during the 1975 and 1976 model years featured three sizes of intake manifold bolts. Tighten the 5/16-inch bolts to between 21 and 25 foot-pounds of torque. Tighten the 3/8-inch bolts to between 27 and 33 foot-pounds of torque. Tighten the 1/4-inch bolts to between 6 and 9 foot-pounds of torque.
Although torque specifications are generally thought of as important when installing the engine's main components, a number of other components are also assigned torque specifications on the 351W, including the spark plugs, the flywheel bolts, the rocker arm cover bolts and the vibration damper's single bolt. Tighten the spark plugs to between 15 and 20 foot-pounds of torque for all years except those 351s produced during 1975 and 1976. Tighten the plugs to between 10 and 15 foot-pounds of torque for the 1975 and 1976 models. Take particular care when tightening the spark plugs, as they can break. Tighten the flywheel bolts to between 75 and 85 foot-pounds of torque. Tighten the rocker arm cover bolts to between 3 and 5 foot-pounds of torque. Finally, tighten the vibration damper bolt to between 70 and 90 foot-pounds of torque.
- "Motor's Auto Repair Manual, 39th Edition"; Motors; 1976