Note: This procedure does not apply to 16-valve engines. Broken valve springs and defective valve stem seals can be replaced without removing the cylinder head. These operations require special tools and compressed air.
1. Remove the cylinder head cover (see Section 4).
2. Remove the spark plugs from the cylinders that have defective parts. If the valve stem seals need to be replaced, all the spark plugs must be removed to supply compressed air.
3. Rotate the crankshaft until the desired piston is at TDC of the compression stroke (see Section 3). If replacing valve stem seals, start with the first cylinder and move from cylinder to cylinder in the order of work.
4. Screw the nipple into the spark plug hole and connect it with a hose to a source of compressed air.
5. Remove the rocker arm axle assembly.
6. Supply compressed air to the cylinder.
Warning: The piston may be driven by compressed air and the engine may suddenly start to rotate.
7. The valves will be held in place by compressed air. If there is wear in the valve/valve seat pair and air leaks are significant, and the compressed air pressure is not enough to hold the valves, use the other method described below.
8. If a source of compressed air is not available, you can use another method. Bring the piston close to TDC. Then, through the spark plug hole, insert a nylon cord into the cylinder until it fills the combustion chamber.
Make sure the end of the cord protrudes from the hole enough to easily remove it from the cylinder. Then turn the engine until there is slight resistance from the cord.
9. Cover all openings in the head with rags to prevent valve mechanism parts from getting in and use a puller to compress the valve springs. Remove the crackers.
Note: A pair of wrenches of the appropriate size can be used to compress the springs.
10. Remove the valve springs, then remove the valve stem seal from the valve guide.
Note: If, after removing the springs and valve stem seal, the air pressure is not sufficient to hold the valve closed, this may indicate wear of the valve/valve seat pair or cylinder-piston group, which will require removal of the head and additional repair work.
11. Place a rubber ring on the valve stem or wrap the stem with electrical tape to prevent the valve from falling and release the air pressure.
Note: If cord was used instead of air, pull the plunger back slightly to release the valves.
12. Inspect the valve stem. Determine the presence of wear or bends by rotating the valve in the guide.
13. Move the valve up and down and check for sticking. If sticking is detected, it may indicate a bent valve stem or damaged guide. In this case, the cylinder head must be removed and additional repair operations must be performed.
14. Re-inject air into the cylinder (or tighten the valves with a piston). remove the rubber ring from the valve stem.
15. Lubricate the valve stem with engine oil and install a new valve stem seal.
Note: The intake and exhaust valve stem seals are not interchangeable: the intake valve stem seal has a white spring, the exhaust valve stem seal has a black spring.
16. Install the valve springs.
Note: Try to align the ends of the springs with the painted marks on the cylinder head.
17. Install the spring plates. Compress the springs and insert the crackers into their grooves. To facilitate fixing the crackers on the valve stem, lightly lubricate the inner surface of the crackers with consistent grease.
18. Remove the compression force from the springs and make sure that the crackers are in place.
19. Remove the air pressure and unscrew the nipple from the spark plug hole (or pull the cord out of the cylinder).
20. Install the rocker arm axle assembly (see Section 10).
21. Install the spark plugs.
22. Install the cylinder head cover (see Section 4).
23. Start the engine, check for oil leaks and extraneous knocks under the cylinder head cover when the oil reaches operating temperature.