Valve Clearance: Adjustments

Fig. 8 Valve adjustment. 4-112, 121 overhead valve engines:

Fig. 7 Aligning crankshaft pulley timing marks. 4-112, 121 overhead valve engines:

4-112, 121 OVERHEAD VALVE ENGINES

4-112, 121 overhead valve engines are also equipped with hydraulic valve lifters which do not normally require adjustment. However, if cylinder head or valve train require service, adjust as outlined.

1. Crank engine until mark on crankshaft pulley is aligned with TDC mark on timing tab. Check to ensure engine is in the No. 1 cylinder firing position by placing fingers on No. 1 cylinder rocker arms as mark on pulley comes near TDC mark on timing tab. If valves are not moving, the engine is in the No. 1 firing position. If valves move as pulley nears TDC mark on timing tab, engine is in No. 4 cylinder firing position and should be rotated one revolution to reach the No. 1 cylinder firing position. The crankshaft pulley contains two sets of marks 180° apart. Use those marks which cut across entire length of pulley to find No. 1 cylinder firing position, Fig. 7.
2. With engine in No. 1 cylinder firing position, adjust the following valves: Exhaust: 1, 3; Intake: 1, 2. To adjust valves, back off adjusting nut until lash is felt at pushrod, then tighten adjusting nut until all lash is removed, Fig. 8. This can be determined by rotating the pushrod while tightening the adjusting nut. When all lash has been eliminated, the pushrod will no longer rotate, Fig. 8. After all lash is eliminated, tighten adjusting nut an additional 11/2 turns.
3. Crank engine one full revolution until mark on crankshaft pulley and TDC mark are again aligned. This is the No. 4 cylinder firing position. With engine in this position, the following valves can be adjusted: Exhaust 2, 4; Intake 3, 4.
4. Install rocker arm cover, then start engine and check timing and idle speed.