Attention! These parts can be removed without removing the cylinder head. To do this, the valve must be held with compressed air or a special device.
Attention! Broken valve springs and damaged valve stem seals can be replaced without removing the cylinder head. To do this, you need compressed air and a hose with a fitting that is screwed into the hole for the candle. In the absence of a compressor, the valve can be held with a piece of thick nylon cord.
1. Remove the cylinder head cover.
2. Remove the spark plug from the cylinder on which the parts of the valve mechanism will be changed, or all the candles if all caps will be changed.
3. Set the piston of the desired cylinder to TDC on the compression stroke. If all valve stem seals will be changed, then start the replacement from the 1st cylinder and then change sequentially, setting each cylinder to TDC in accordance with the engine operation order.
4. Screw adapter GM N J-23590 or equivalent into the spark plug hole (see photo).
5. Turn away a nut and remove a spherical axis and a yoke of the necessary valve, and get a pusher bar. If the valve stem seals of all valves are changed, then remove all rocker arms and pushers.
6. Apply compressed air to the cylinder. Valves must be held by air pressure. If the valves and seats burn, the tightness of the combustion chamber will be insufficient, which indicates the need to repair the valves and seats.
7. If compressed air is not available, set the piston just before TDC on the compression stroke, then thread a nylon cord through the spark plug hole until the cord fills the combustion chamber. Make sure the end of the cord comes out of the hole. Rotate the crankshaft in the direction of normal rotation until a slight resistance is felt (as the piston begins to rest against the cord in the combustion chamber).
8. Close the openings of the cylinder head around the valves with a rag to prevent the removed parts from getting into the combustion chambers, compress the valve spring using a tool and remove crackers (see photo).
9. Release the valve spring, remove the spring plate or valve rotator, spring and oil deflector, remove the valve stem seal. Three different types of caps are used on the engines in question, depending on the year of manufacture, displacement and power. As a rule, ring caps are installed, which are put on the guide sleeve. Flat seals are also used, which are inserted into the groove on the valve stem directly below the cracker groove (see photo). Umbrella caps are provided on some of the engines (see photo). Umbrella caps are most often installed together with flat seals. Flat seals tend to harden and will break when removed. When disassembling, they should always be replaced.
10. Wrap tape around the top of the valve stem to prevent it from falling into the combustion chamber, then relieve pressure or remove the cord from the combustion chamber.
11. Check valve condition (rod bending and wear), moving it up and down in the sleeve, turning and shaking. If seizing or excessive play is felt, the cylinder head should be removed and repaired.
12. Examine an axis of a yoke. Worn axles on engines of 5.0 and 5.7 liters are changed only in a car service, since the depth of their pressing must be maintained with high accuracy. On some 7.4 liter engines, as well as on a small part of 5.0 and 5.7 liter engines (the latter are not installed on trucks) the ball shafts of the rocker arms are threaded and can be replaced. In addition, some designs include a guide bushing that fits between the rocker shaft and the cylinder head to help center the push rod relative to the rocker arm. When turning out the ball axles, this bushing must be replaced. Axes wrap on sealant.
13. Remove the adhesive tape from the valve and install the new spring, cracker, cap and other removed parts in the reverse order, supplying compressed air or introducing a cord-like packing into the combustion chamber. When assembling, it is recommended to lubricate the crackers with grease to fix them (see photo), lubricate the valve stems with engine oil. When finished, relieve pressure or remove packing.
14. Reinstall the cylinder head cover, wrap the candles and attach the wires to them. Attach all hoses and tubes. Start the engine, check for leaks and abnormal noises coming from the valve train.