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 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 one 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.ADJUSTMENT
610, 710 and 1977-80 510, 200SX (Single Plug Engine)
- The valves are adjusted with the engine at normal operating temperature. Oil temperature, and the resultant parts expansion, is 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 seal before removing the camshaft cover. Note the location of any wires and hoses which may interfere with cam cover removal, disconnect them and move them aside. Then remove the bolts which hold the cam cover in place and remove the cam cover.
- Place a wrench on the crankshaft pulley bolt and turn the engine over until the valves for 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.
- Check the clearance of the intake and exhaust valves. You can differentiate between them by lining them up with the tubes of the intake and exhaust manifolds. The correct size feeler gauge should pass between the base circle of the cam and the rocker arm with just a slight drag. Be sure the feeler gauge is inserted straight and not on an angle.
- If the valves need adjustment, loosen the locking nut and then adjust the clearance with the adjusting screw. You will probably find it necessary to hold the locking nut while you turn the adjuster. After you have the correct clearance, tighten the locking nut and recheck the clearance. Remember, it's better to have them too loose than too tight, especially exhaust valves.
- Repeat this procedure (Steps 3-5) until you have checked and/or adjusted all the valves. (Be sure to adjust in the firing order.) Keep in mind that all that is necessary is to have the valves closed and the camshaft lobes pointing up.
- Install the cam cover gasket, the cam cover, and any wires and hoses which were removed.
The 810 and Maxima engine valves are adjusted hot.
- Note the locations of all hoses or wires that would interfere with valve cover removal, disconnect them and move them aside. Then, remove the six bolts which hold the valve cover in place.
- Bump one end of the cover sharply to loosen the gasket and then pull the valve cover off the engine vertically.
- Place a wrench on the crankshaft pulley bolt and turn the engine over until the first cam lobe is pointing straight up. The timing marks on the crankshaft pulley should be lined up approximately where they would be when the No. 1 spark plug fires.
If you decide to turn the engine by bumping it with the starter, be sure to disconnect the high tension wire from the coil to prevent the engine from accidentally starting and spewing oil all over the engine compartment. Never attempt to turn the engine by using a wrench on the camshaft sprocket bolt. This would put a tremendous strain on the timing chain.
- See the illustration for primary adjustment and check the clearance for valves (1), (3), (7), (8), (9) and (11) using a flat bladed feeler gauge. The feeler gauge should pass between the cam and the cam follower with a very slight drag. Insert the feeler gauge straight, not at an angle.
A narrow angled feeler gauge blade should be used to fit in the slot of the cam follower. Do not angle the feeler gauge when checking the clearance.
- If the clearance is not within the specified limits, loosen the pivot locking nut and then insert the feeler gauge between the cam and the cam follower. Adjust the pivot screw until there is a very slight drag on the gauge, tighten the locking nut, recheck the adjustment and correct as necessary.
- Turn the engine over so that the first cam lobe is pointing straight down. See the illustration for secondary adjustment and then check the clearance on valves (2), (4), (5), (6), (10) and (12). If clearance is not within specifications, adjust as detailed in Step 5.
- Clean all traces of old gasket material from the valve cover and the head. Install the new gasket in the valve cover with sealer and install the valve cover. Tighten the valve cover bolts evenly in several stages going around the cover to ensure a good seal. Reconnect all hoses and wires securely and operate the engine to check for leaks.
- Road test the vehicle for proper operation.
- The valves must be adjusted with the engine warm, so start the car and run the engine until the needle on the temperature gauge reaches the middle of the gauge. After the engine is warm, shut it off.
- Purchase either a new gasket or some silicone gasket sealer before removing the camshaft cover. Counting on the old gasket to be in good shape is a losing proposition. Always use new gaskets. Note the location of any wires and hoses which may interfere with cam cover removal, disconnect them and move them to one side. Remove the bolts holding the cover in place and remove the cover. Remember, the engine will be hot, so be careful.
- Place a wrench on the crankshaft pulley bolt and turn the engine over until the first cam lobe behind the camshaft timing chain sprocket is pointing straight down.
If you decide to turn the engine by bumping it with the starter, be sure to disconnect the high tension wire from the coil(s) to prevent the engine from accidentally starting and spewing oil all over the engine compartment. Never attempt to turn the engine by using a wrench on the camshaft sprocket bolt. There is a one to two turning ratio between the camshaft and the crankshaft which will put a tremendous strain on the timing chain.
- See the illustration for primary adjustment and check the clearance of valves (1), (4), (6), and (7) using a flat bladed feeler gauge. The feeler gauge should pass between the valve stem end and the rocker arm screw with a very slight drag. Insert the feeler gauge straight, not at an angle.
- If the clearance is not within specified value, loosen the rocker arm locknut and turn the rocker arm screw to obtain the proper clearance. After correct clearance is obtained, tighten the locknut.
- Turn the engine over so that the first cam lobe behind the camshaft timing chain sprocket is pointing straight up and check the clearance of the valves marked (2), (3), (5), and (8) in the secondary adjustment illustration. They, too, should be adjusted to specifications as in Step 5.
- Install the cam cover gasket, the cam cover and any wires and hoses which were removed.