Valve spring and defected valve stem seals can be retailed just by changing the gasket, it only involves 2 tools and air compressor. Start by unbolting the valve cover from the cylinder head and, if you are dealing with a V6 car which has all the stem seals' replacement, the removal of both valve covers is expected. Subsequently, unthread the spark plug situated in the cylinder in question and, in case of replacement of all seals, undo all the spark plugs. Rotate the crankshaft of the engine until top dead center of piston of the cylinder in question on the end of the compression stroke with cylinder 1 and further by firing order. Insert an adapter in the spark plug hole and attach an air line connected to a compressed air. If one cannot have compressed air, put the piston approximately 45 degrees before the TDC on the compression stroke and insert a long nylon rope through the spark plug hole to the combustion chamber and allow the strand of nylon rope to hang out for easy retrieval. There are metal trims usually located round the valve spring area; use shop rags to pack the holes in the cylinder head to avoid dropping of the various parts Go ahead and compress the spring and remove the keepers using a valve spring compressor. Pull the spring retainer, shield, and the valve spring and then pop out the umbrella type guide seal. If the air pressure could not close the valve tight, the valve face or seat could be damaged and required head off for further work. Put a band or tape around the top of the valve stem to avoid dropping it in to the combustion chamber and deflate the tire. Check for any blemish on the valve stem; if the stem gives a binding impression in the guide then the head has to be detached to be rectified. Applying pressure with air to keep the valve closed then you can take off the tape or rubber band that you used. Turn the valve stem clockwise to coat it with engine oil and fit a new guide seal: some differ between the intake and exhaust sides. Again, orient the spring and cover the valve and then, the spring retainer pushing the spring to align the keepers at the groove, use a little grease to hold the keepers flat. Now you can take off the pressure from the spring tool in order to let the keepers sit in their place, then it is just disconnected the air hose and pulled out the adapter from the spark plug hole. Last of all, put in the rocker arm(s), spark plug(s) incorporating their wire(s), valve cover(s) and commence the engine and look out for any traces of oil leakages; or any strange noises originating from the vicinity of the cover.
