A worn out valve spring or a rotten valve stem seal can often be replaced without the need to pull the cylinder head; and if it is done, two special tools plus compressed air are used. In case compressed air is not available, it is possible to use a nylon rope of some length to keep the valves from falling into the cylinder. Start by pulling off both valve covers if all valve stem seals are being changed then pull out spark plug from the said cylinder or all the power spark plugs if the need arises. But before doing this, rotate the crankshaft until the piston, on the respective cylinder you are working on, is on TDC on the compression stroke, this should be done cylinder by cylinder as outlined in the firing order. In the spark plug hole an adapter must be screwed into for an air hose connected to a source of compressed air. Lever off the bolt, pivot, and rocker arm of the faulty valve and . Since it is usually impossible to turn the valves using compressed air many people, use of nylon rope is recommended on condition that the rope will occupy the combustion chamber but one end will remain outside. Avoid the loss of parts into the engine by packing the holes at the cylinder head with shop rags, then using the valve spring compressor to compress the spring and for you to remove the keepers. In case the air pressure cannot keep the valve closed the face or the seat of the valve would be injured such that the cylinder head would have to be removed before repairs can be accomplished. Secure the valve stem by putting rubber band or any tape in order to avoid the stem from falling and then deflate the tyre. On the valve stem check for the eccentric movement of the valve and the binding of the stem. Pull off the pressure to keep the valve closed and then remove the tape or rubber band used. Coat the valve stem with a thin layer of engine oil and then replace the worn seal with new one but is important to make sure that the right seal is fitted to the intake and exhaust valves. Fit the spring/damper assembly and the valve spring retainer and squish the assembly towards the head and engage the keepers in the upper slot. Then, having made sure that the keepers are in their places, shut off the air hose and take the adapter out of the spark plug hole. Replace the rocker arm(s) and pushrod(s) next reinsert the spark plug(s) and reconnect the wire(s). Last of all, turn on the engine, look for signs of oil dripping and strange noises coming from the top of the engine, around the valve cover.