GENERAL INFORMATION 1970-83 Models
Valve adjustment determines how far the valves enter the cylinder and how long they stay open and closed.
If the valve clearance is too large, part of the lift of the camshaft will be used in removing the excessive clearance. Consequently, the valve will not be opening for as long as it should. This condition has two effects:
- The valve train components will emit a tapping sound as they take up the excessive clearance.
- The engine will perform poorly because the valves don't open fully to allow the proper amount of gases to flow through the engine.
If the valve clearance is too small, the intake and the exhaust valves will open too far and will not fully seat on the cylinder head when they close. When a valve seats itself on the cylinder head, it does two things:
If the valve clearance is too small, the engine will run poorly because of the gases escaping from the combustion chamber. The valves will also become overheated and will warp, since they cannot transfer heat unless they are touching the valve seat in the cylinder head.
While the valve adjustments must be made as accurately as possible, it is better to have the valve adjustment slightly loose rather than tight, as a burned valve may result from overly tight adjustments.
See Figures 1, 2, 3, 4 and 5
The valves are adjusted with the engine at normal operating temperatures. The oil temperature (and the resultant parts expansion) are much more important than water temperature.
- Run the engine for at least fifteen minutes to ensure that all the parts have reached their full expansion. After the engine is warmed up, shut it off.
- Purchase either a new gasket or some silicone gasket sealant before removing the camshaft cover. Note the location of any wires and hoses which may interfere with the cam cover removal; tag, disconnect and move them aside. Remove the cam cover bolts and the cover.
- Place a wrench on the crankshaft pulley bolt and rotate the engine until the valves for the No. 1 cylinder are closed. When both cam lobes are pointing up, the valves are closed.
If you have not done this before, it is a good idea to turn the engine over slowly several times and watch the valve action until you have a clear idea of just when the valve is closed.
- Adjust the clearance of only half of the valves, specifically Nos. 1, 3, 7, 8, 9 and 11, as illustrated.
- Using a feeler gauge, measure the clearance between the cam lobe and the valve rocker. The clearance should be 0.4mm for intake valves 1, 7 and 9, and 0.30mm for exhaust valves 1, 7 and 9. All measurements should be made when the engine is hot.
- If the clearance is not the specified value, loosen the pivot locknut and turn the valve rocker pivot to provide proper clearance. The feeler gauge should move with a very slight drag when rechecked.
- Turn the crankshaft (again) so that the high point of the No. 1 cam lobe points down. Adjust the clearance of the other valves (2, 4, 5, 6, 10 and 12) using the same procedure as in Step 6. The clearance should be 0.4mm for intake valves 2, 5 and 10, 0.30mm; for exhaust valves 4, 6 and 12.
- Install the cam cover gasket, and cam cover, then any wires and hoses which were removed.
The 1984 and later models have hydraulic valve lifters. Periodic adjustment is not necessary.