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.
2.1L Diesel Engine
See Figure 1
The 2.1L Diesel engines have adjustable valves. All other engines have hydraulic valve lifters which maintain a zero clearance and cannot be adjusted.
- Be sure that the engine is cold before adjusting the valves. Remove the valve cover.
- Set the No. 1 cylinder to TDC on the compression stroke. Check the valve clearance of number one and number two intake, and number one and number three exhaust valves. Adjust as required.
The No.1 cylinder is located at the flywheel end of the engine.
- Rotate the crankshaft 360°, then check the clearance of the number three and number four intake, and number two and number four exhaust valves. Adjust as required.
- To adjust, loosen the locknut and turn the adjustment screw as necessary. As each adjustment screw is tightened, be sure that the bottom of the screw is aligned with the valve stem. If the adjustment screw is not aligned with the stem when tightened, the stem could bend. Tighten the locknut.
- The exhaust valve adjustment specification is 0.010 in. (0.25mm). The intake valve adjustment specification is 0.008 in. (0.20mm)