GM 12621428 Spring, Valve

Valve springs break and valve stem seals can be changed without removing a cylinder head, generally, two special tools and compressed air. First, the spark plugs and valve covers shall be unplugged and by turning the crankshaft of the vehicle, the piston number one should be on the compression stroke TDC. Take out the rocker arms for the number one cylinder, insert an adapter into the spark plug hole and attach an air line from compressed air. Using compressed air jam the valves on the cylinder and for the cylinder head hole stuff the shop rags so as to avoid oil and other parts or tools to fall on the engine. Lightly hammer on the heads of the valve springs with a soft-faced hammer to free the valve keeper from its seat on the spring retainer with a magnet or with small needle-nose pliers using a valve-spring compressor. Lift off the valve spring and the retainer and if air pressure cannot keep the valve closed the valve face or seat may be bent and will require the cylinder head to be pulled for repairs. Take out the previous valve stem seals with the typical variation between the intake and the exhaust seals and circle the head of the valve stem with a rubber band or some piece of thin tape so as the top of the valve stem won't fall off into the combustion chamber before one can release the air pressure. Check the valve stem for signs of wear particularly the smooth running of the stem in the guide; if this fails the head will have to be unbolted for further repair. Pump in a little air pressure to lock the valve in its closed position; then, place the new valve stem seals over the ends of the intake and exhaust valve guides. Place the keepers alongside the retainer and over the valve, compress the valve spring assembly enough through to seat the keepers and use a drop of grease just to ensure that they are well in place. Retract the keepers and take off the pressure from the spring tool, thereafter, take off the air hose and remove the adapter from the spark plug hole. Perform the same on the other cylinders, with each piston at TDC on the compression stroke when air pressure is applied and the rocker arm assemblies and valve covers fitted back.

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.

Inspect the valve stem for damage and ensure it does not bind in the guide; if it does, the head will need to be removed for repair.