Valve Clearance: Adjustments

INITIAL ADJUSTMENT

1. With engine in position to fire No. 1 cylinder, adjust the following valves: 4.3L/V6-262 engines, Exhaust Nos. 1, 5 and 6; Intake Nos. 1, 2 and 3. 4.8L/6-292 engines, Exhaust Nos. 1, 3 and 5; Intake Nos. 1, 2 and 4. V8 engines, Exhaust Nos. 1, 3, 4 and 8; Intake Nos. 1, 2, 5 and 7.
2. To properly adjust valves back off adjusting nut until lash is felt, (when push rod can be rotated by hand), then tighten nut until lash is eliminated.
3. When zero lash is acquired, tighten adjusting nuts additionally as follows: All except 7.4L/V8-454 engine, tighten nut one full additional turn from zero lash. On 7.4L/V8-454 engine tighten nut 3/4 additional turn from zero lash.
4. On all engines, turn crankshaft one complete revolution, which will bring engine in position to fire cylinders 4 (V6) or 6 (Inline 6 and V8).
5. With engine in this position, adjust the following valves: 4.3L/V6-262 engines, Exhaust Nos. 2, 3 and 4; Intake Nos. 4, 5 and 6. 4.8L/6-292, Exhaust Nos. 2, 4 and 6; Intake Nos. 3, 5 and 6. V8 engines, Exhaust Nos. 2, 5, 6 and 7; Intake Nos. 3, 4, 6 and 8.
6. When zero lash is acquired, tighten adjusting nuts additionally as specified in step 3.

FINAL ADJUSTMENT

1. After engine has been warmed to operating temperature, remove valve cover.
2. With engine running at idle speed, back off valve rocker arm nut until rocker arm starts to clatter.
3. Turn rocker arm nut down slowly until the clatter just stops. This is the zero lash position.
4. Turn nut down 1/4 additional turn and pause 10 seconds until engine runs smoothly. Repeat additional 1/4 turns, pausing 10 seconds each time, until nut has been turned down as specified: All except 7.4L/V8-454 engine, tighten rocker nut one full additional turn from zero lash; On 7.4L/V8-454 engine tighten rocker nut 3/4 additional turn from zero lash. This preload adjustment must be done slowly to allow the lifter to adjust itself to prevent the possibility of interference between the intake valve head and top of piston, which might result in internal damage and/or bent pushrods. Noisy lifters should be replaced.
5. Install valve cover, with new gasket.

VALVE ROTATORS

Fig. 18 Valves and Components:

The parts involved in the rotating mechanism, Fig. 18, are a special spring seat retainer, a pair of flat half-moon keys, a close fitting cap located on the valve stem and a specially constructed valve stem.
In order to accommodate valve expansion, the valve lash must be maintained. When camshaft rotation causes this lash or clearance to be taken up, the cap on the valve stem causes the valve keys to raise the spring retainer, removing the load on the valve springs from the valve before the valve is moved from its seat. A clearance of .002-.004 inch should be maintained between the end face of the valve stem and cap. This is the distance the spring retainer is moved before the valve is moved. The slow valve rotating motion is caused by the vibration of the valve, the flowing of exhaust gases around the valve head, and a slight rotating motion imparted to the valve by the valve spring.
Whenever valve work is being done, a check for clearance should be made by holding the assembled valve and rotating mechanism in the hands. With one hand, press down on the valve cap and turn the valve with the other hand. If the valve turns readily, it indicates that there is clearance present.
A special gauge is available to check this clearance. If the gauge indicates no clearance, grind off the end of the valve stem. If the clearance is too great, grind off the open end of the valve cap.

VALVE GUIDES

Valve guides in these engines are an integral part of the head and, therefore, cannot be removed. For service, guide holes can be reamed oversize to accommodate one of several service valves with oversize stems.
Check the valve stem clearance of each valve (after cleaning) in its respective valve guide. If the clearance exceeds the service limits of .004 inch on the intake or .005 inch on the exhaust, ream the valve guide to accommodate the next oversize diameter valve stem.
Select the reamer for the smallest oversize which will provide a clean straight bore through the valve guide. After reaming, a new seat should be cut into the head to assure perfect seating of the new valve.