Note: Broken valve springs and damaged valve stem seals can be replaced without removing the cylinder head. This operation typically requires two special tools and a source of compressed air, so review this section carefully and borrow or purchase the necessary equipment before beginning. If a source of compressed air is not available, use a piece of nylon cord to prevent the valves from falling into the cylinder during operation.
1. Remove the valve cover from the corresponding cylinder head (see section 4).
2. Remove the spark plug from the cylinder with damaged parts. If it is necessary to replace the seals on all valve stems, remove the spark plugs from all cylinders.
3. Turning the crankshaft, set the piston in the cylinder with damaged parts to the TDC position on the compression stroke (see section 3). If you are replacing the seals on all the valve stems, start with cylinder 1 and continue replacing them on the others one by one. Move from one cylinder to another, observing the sequence of their operation (see technical data given in this chapter).
4. Screw the adapter into the spark plug hole (see illustration) and connect a hose from a compressed air cylinder to it. Note: Most compression testers come with a screw-on adapter that fits into the quick-release end of the air hose.
7.4. This is what the adapter to the air hose looks like, which is screwed into the hole for the spark plug
5. After unscrewing the nut, remove the struts and valve rocker arm and take out the rod. If it is necessary to replace the seals on all valve stems, then all valve rocker arms and rods must be replaced at the same time (see section 6).
6. Direct a stream of compressed air into the cylinder.
Caution! The air flow may cause the cylinder to move downwards, resulting in sudden crankshaft rotation. If the wrench used to set the cylinder to TDC has not been removed from the end of the crankshaft, it may cause injury when turning the shaft.
7. The valves must be held in place by air pressure. If the technical condition of the working surfaces or valve seats is unsatisfactory, then due to air leakage the jet pressure will be insufficient to hold the valves. In this case, it is necessary to use a different method.
8. If there is no compressed air source, position the piston approximately 45° short of TDC on the compression stroke, then push the end of a long nylon cord into the spark plug hole until it fills the combustion chamber. The other end of the cord must remain outside the engine, otherwise it will be difficult to reach. Using a ratchet wrench, turn the crankshaft in the direction of rotation until you feel slight resistance to turning.
9. Stuff rags into the cylinder head openings above and below the valves to prevent parts from falling out of the engine, and compress the valve spring using a special tool. Remove the crackers.
Note: There are two types of devices for compressing valve springs with the cylinder head on. One of them works on the principle of gripping the lower coils of the spring and pressing on the spring plate when turning the handle. The second device is a lever type; here the stud and nut of the valve rocker arm are used as a stop (see illustration). Both devices are quite effective, but the cost of the second one is usually somewhat lower.
7.9. To replace the valve cuff or valve springs without removing the cylinder head, you need to use a special tool to press the spring and remove its crackers
10. After removing the spring plate, boot and valve spring, remove the cuff (see illustration).
Note: If the air flow is not strong enough to hold the valves closed during this operation, the valve seat or face may be damaged. In this case, the cylinder head should be removed to perform additional repair work.
7.10. Valve spring with adjacent parts: 1 - crackers, 2 - spring plate, 3 - sealing ring, 4 - cover, 5 - valve spring
11. Wrap a rubber band around the top of the valve stem to prevent the valve from falling into the combustion chamber, then reduce the air pressure.
Note: If a nylon cord rather than an air jet was used, turn the crankshaft slightly in the opposite direction to normal rotation.
12. Check the valve stem for damage. By turning the valve in the guide bushing, check its tail for eccentricity. The presence of eccentricity may indicate that the valve stem is bent.
13. Move the valve up and down in the guide sleeve to check if it is sticking. The presence of sticking means that either the valve stem is bent or its guide bushing is damaged. In both cases, the cylinder head will have to be removed to perform additional repair work.
14. Again apply compressed air to the cylinder to hold the valve closed and remove the rubber band from the valve stem. If you used a nylon cord instead of an air jet, turn the crankshaft in the normal direction of rotation until you feel a slight resistance to rotation.
15. Apply a layer of engine oil to the valve stem and install a new seal.
16. Place the spring with the cover on top of the valve.
17. Install the spring plate. While compressing the valve spring, carefully insert the crackers. To prevent the crackers from falling out during assembly, put a small amount of grease in them (see illustration).
7.17. The crackers do not always stay in place on their own, so before assembling them, put a drop of grease in each of them, as shown in the photo: thanks to this, they will stay on the valve stem until the spring is installed
18. By releasing the pressure of the device on the spring, make sure that the crackers are in place.
19. Disconnect the air hose and unscrew the adapter from the spark plug hole. If a nylon cord was used instead of compressed air to perform these tasks, remove it from the cylinder.
20. Install the valve rocker arm and rod (see section 6).
21. Screw in the spark plugs and connect the spark wires to them.
22. Install the valve covers (see section 4).
23. Start the engine and let it run for a while, then check the valve train for oil leaks or unusual noises coming from the head cover area.