GM 12621428 Spring, Valve

Well-worn valve springs and valve stem seats that do not seat properly can be repaired with the head off and often do not need to be removed, but require two special tools and compressed-air source. Start by pulling out the spark plug and the valve cover, crank the engine in order to align the number one piston on the compression stroke. Then, you have to take out the rocker arms which are used for the number one cylinder and fit an adapter to the spark plug hole and attach a hose to it for an air compressor from a compressed air supply. Use compressed air to close the valves and make them stay in position; use shop rags to block all the spaces of the cylinder head round the valves to ensure that no part and tool fall in the engine. Simply strike lightly on top of the valve spring retainer to remove the check between the valve keeper and the spring retainer, then make use of a valve spring compressor to compress the spring and then remove the keeper using a small needle nose pliers or magnet. Pull out the valve spring and the retainer by pulling carefully to prevent the valve from being struck by the falling spring and bending. Take off the old valve stem seals and notice that the intake is always different from the exhaust, and put a rubber band or a piece of tape around the top of the valve stem so that it does not fall into the combustion chamber when you release the air pressure. Check the condition of the valve stem , it should not stick in the guide. Apply air pressure to keep the valve shut; replace the valve stem seals, the spring and retainer. Slightly compress the valve spring assembly to fit in the keepers and use a tiny amount of grease to fix them if required. Subsequently, if the keepers are comfortably seated, shut off the line of air and take off the adapter from the surface of the spark plug. Perform same procedure on the rest of cylinders with regards to firing order sequence; then install the rocker arm assembly and the valve covers. Last, engage the engine and look for traces of oil or strange sounds and rev the engine for not less than five minutes.

If air pressure fails, the valve face or seat may be damaged, necessitating cylinder head removal for repair.