Valve springs get broken while valve stem seals become defective; these can be repaired without having to remove the cylinder head; usually, it takes two special tools and compressed air. If compressed air is not available then it is recommended to use a length of nylon rope to stop the valves from falling in the cylinder. To start with, unbolt the valve cover from the corresponding cylinder head and, if all the valve stem seals are going to be replaced, take off both. Subsequently, examine the particular cylinder incorporating the defective element and remove the spark plug; if replacing all seals, eradicate all spark plugs. They rotate the crankshaft until the piston of the particular cylinder, which is to be checked, is at the top dead center on TDC of the compression stroke, although it must be noted that it is done cylinder by cylinder in the firing order. Insert an adapter into the spark plug hole and attach an airline to compressed air. Loosen the bolt at the top of the valve, the pivot and rocker arm, and the pushrod of the valve with the defective part. Use air pressure at the cylinder to maintain the position of the valves. When using the nylon rope, place the piston at about 450 between TDC, string through the spark plug hole then turn the crankshaft in an anti-clockwise direction until some resistance is met. Also, to avoid dropping some parts inside the engine, stuff shop rags into the cylinder head holes When using the spring/damper tool, remove the compressors on the keepers. Whenever pressure fails to keep the valve shut you are likely to see the face or the seat of the valve suffer considerable damage, which may call for the entire cylinder head to be removed to allow access to other repair procedures. Tape a rubber band or stick a strip of tape onto the end of the valve stem so that it won't drop in to the combustion chamber then relieve the air pressure. Check the valve stem for any signs of wear or of seizing in the guide and if it is the case, the head will have to be taken off for servicing. Applying pressure on the air to keep the valve closed and untie the tape or rubber band which was used. The next step is to add engine oil to the valve stem then put a new seal to the guide and be certain that the appropriate seal is utilized for each valve. Place the spring/damper assembly over the valve, then, the valve spring retainer should be fitted and compressed. Place the keepers in the upper groove and if needed use the grease to keep the keepers in place and then release the pressure on the spring tool. Slacken the connecting air hose and withdraw the adapter out of the spark plug hole or jerk out the rope if utilized. Last but not the least reinstall the rocker arm and pushrod and tighten the bolts, then fix the spark plug and wires and finally fit the valve cover before starting the engine and check for oil leaks or any unusual sound emanating from the valve cover region.
