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 as far as it should. This condition has two effects: the valve train components will emit a tapping sound as they take up the excessive clearance and the engine will perform poorly because the valves don't open fully and allow the proper amount of gases to flow into and out of the engine.
If the valve clearance is too small, the intake valves and the exhaust valves will open too far and they will not fully seat on the cylinder head when they close. When a valve seats itself on the cylinder head, it does two things: it seals the combustion chamber so that none of the gases in the cylinder escape and it cools itself by transferring some of the heat it absorbs from the combustion in the cylinder to the cylinder head and to the engine's cooling system. 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 all valve adjustments must be made as accurately as possible, it is better to have the valve adjustment slightly loose than slightly tight, as a burned valve may result from overly tight adjustments.
The 4-134 F-Head, 6-226 L-head, 6-230 OHC engines have adjustable valves. All other engines have hydraulic valve lifters which maintain a zero clearance.
These hydraulic lifters are set after overhaul, by bringing the piston to TDC compression and turning the nut until the rocker arm just touches the valve stem, then 1 / 2 turn more.
ADJUSTMENT 4-134 F-Head Models
The engine must be cold (at air temperature) when the valves are adjusted on the F-Head engine.
- Remove the side valve spring cover.
- After the engine has cooled to ambient temperature, turn the engine until the lifter for the front intake valve is down as far as it will go. The lifter should be resting on the center of the heel (back) of the cam lobe for that valve. You can observe the position of the lifter by looking through the side valve spring cover opening.
- Put the correct size feeler gauge between the rocker arm and the valve stem for that particular intake valve. There should be a very slight drag on the feeler gauge when it is pulled through the gap. If there is a slight drag, you can assume that the valves are at the correct setting. If the feeler gauge cannot pass between the rocker arm and the valve stem, the gap between them is too small and must be increased. If the gauge can be passed through the gap without any drag, the gap is too large and must be decreased.
- Loosen the locknut on the top of the rocker arm (pushrod side) by turning it counterclockwise.
- Turn the adjusting screw clockwise to lessen the gap and counterclockwise to increase the gap. When the gap is correct, turn the locknut clockwise to lock the adjusting screw. Follow this procedure for all of the intake valves, making sure that the lifter is all the way down for each adjustment.
- Turn the engine so that the first exhaust valve is completely closed and the lifter that operates that particular valve is all the way down and on the heel of the cam lobe that operates it.
- Insert the correct size feeler gauge between the valve stem of the exhaust valve and the adjusting screw. This is done through the side of the engine in the space that is exposed when the side valve spring cover is removed. If there is a slight drag on the feeler gauge, you can assume that the gap is correct. If there is too much drag, or not enough, turn the adjusting screw clockwise to increase the gap and counterclockwise to decrease the gap.
- When all of the valves have been adjusted to the proper clearance, replace the valve covers. Always use new valve cover gaskets when replacing the covers.
6-226 L-Head Models
Valves should be adjusted with the engine cold. Access to the valve cover is possible via an access panel in the wheel well. Valves can be adjusted only with the tappet on the low portion of the cam.
- Raise and support the front end on jackstands.
- Remove the right fron