Take off the 
Cylinder Head and lay the head on a vise or any strong table. Utilize a vast clamp type valve spring compressor accompanied by an adapter to crush every valve spring so that lowest portion of the tool must be placed under the certain valve which is being operated and then compress the spring till the keepers are removable by magnet or small pair of pliers. Remove the valve spring together with the retainer pressed to the shank. Pull off the old valve stem oil seal with the help of pliers. V Berkwood et al, Controlling Corrosion Costs in Canada: A Guide, National Corrosion Control Manual this book recommends inspecting the valve and its stem for damage and rotating the valve in the guide to check for any eccentric - this usually indicates a bent valve. Slide the valve to and fro in the guide, if be cannot be done they may be severely fouled or the guide worn, which will require work on the cylinder head. Grease the valve stem with the engine oil and then, before inserting it in the cylinder head, cover it with a new seal with an aid of a plastic seal protector or the cellulose tape to avoid damaging the new seal while it is passing through the keeper grooves. Apply multi-purpose grease on the new seal and fit it over the valve stem while applying a hand force subsequently, the protector or tape should be recovered once the seal has tightened against the guide. Online, using a deep socket of the required measure, you need to gently knock the new seal in the upper part of the valve guide. Place the valve over the spring and ensure the retainer is in place, compress the valve spring and the retainer then put the keepers into the groove and if necessary and the keepers are difficult to put in you can apply some grease. Taking the pressure off the spring tool should guarantee that the keepers are in place. Return the lifters and camshafts back to the original position and perform the following in the exact order they were removed: Crack the throttle and turn on the engine to look for signs of old and fresh oil on the valley area, as well as any abnormal noise coming from the vicinity of the valve cover.