As part of every major tune-up or once every 15,000 miles (24,000 km) the valve clearance should be checked and adjusted if necessary. Valve lash is one factor which determines how far the intake and exhaust valves will open into the cylinder.
If the valve clearance is too large, part of the lift of the camshaft will be used up in removing the excessive clearance, thus the valves will not be opened far enough. This condition has two effects, the valve train components will emit a tapping noise as they take up the excessive clearance, and the engine's performance will suffer, since the less the intake valves open, the smaller the amount of air/fuel mixture admitted to the cylinders will be. The less the exhaust valves open, the greater the back-pressure in the cylinder which prevents the proper air/fuel mixture from entering the cylinder.
If the valve clearance is too small, the intake and exhaust valves will not fully seat on the cylinder head when they close. When a valve seats on the cylinder head it does two things; it seals the combustion chamber so none of the gases in the cylinder can escape and it cools itself by transferring some of the heat it absorbed from the combustion process through the cylinder head and into the engine cooling system. Therefore, if the valve clearance is too small, the engine will run poorly (due to gases escaping from the combustion chamber), and the valves will overheat and burn or warp (since they cannot transfer heat unless they are touching the seat in the cylinder head). While all valve adjustments must be as accurate as possible, it is better to have the valve adjustment slightly loose than slightly tight, as burnt valves may result from overly tight adjustments.
These engines are equipped with hydraulic valve adjusters in the valve train. The adjusters automatically maintain a zero valve clearance between the rocker arm and valve stem and no periodic adjustment is possible or necessary. The best way to maintain hydraulic lash adjusters is through regular and frequent oil and filter changes.Except 2S-E Engine
- Remove the valve cover (cylinder head cover).
- Use a wrench and turn the crankshaft clockwise until the notch in the pulley aligns with the timing mark 0 on the timing belt cover. This will insure that engine is at TDC/compression on No. 1 cylinder.
- Using a flat feeler gauge measure the clearance between the camshaft lobe and the valve lifter. This measurement should correspond to the one given in the "Tune-Up Specifications" chart. Check only these valves listed first: intake side, cylinders No.1 and 2; exhaust side, cylinders No. 1 and 3. Use the illustrations to help you.
- Turn the crankshaft clockwise one complete revolution and realign the timing marks at 0.
- Now check the clearance of only these valves: intake side, cylinders No. 3 and 4; exhaust side, cylinders No. 2 and 4.
- Identify the valve(s) to be adjusted. Turn the crankshaft to position the camshaft lobe of the cylinder to be adjusted, upward.
- Using a small tool, turn the valve lifter so that the notch is easily accessible.
- Use the special tool to press the shim and lifter downward. Use the other tool from the set to hold it in place; make sure the second tool is not resting on the shim you're trying to remove.
- Using a small screwdriver and a magnetic arm or probe, lift the shim up and remove it.
- Measure the thickness of the old shim with a micrometer. Locate that particular measurement in the "Installed Shim Thickness" column of the shim charts, then locate the previously recorded measurement (from Step 3 or 5) for that valve in the "Measured Clearance" column of the charts. Index the two columns to arrive at the proper replacement shim thickness.
- Install the new shim, remove the special tool and then recheck the valve clearance.
- Repeat the procedure for each valve needing adjustment.
- Reinstall the valve cover.