Note. Broken valve springs and damaged valve stem seals can be replaced without removing the cylinder head. Typically, this operation requires two special tools and a source of compressed air, so read this section carefully and borrow or purchase the necessary equipment before starting work. If you do not have a source of compressed air, then use a piece of nylon cord to prevent the valves from falling into the cylinder during operation.
1. Remove the valve cover from the respective cylinder head. If all valve seals will be replaced, remove both valve covers (see section 4).
2. Remove the spark plug from the cylinder. If it is necessary to replace the cuffs on all valve stems, turn out the candles from all cylinders.
3. Turning the crankshaft, set the piston to the TDC position on the compression stroke (see section 3). If you are replacing the cups on all valve stems, start with the 1st cylinder and continue replacing the rest in turn. Move from one cylinder to another, following the sequence of their work (see technical data).
4. Screw the adapter into the spark plug hole (see illustration) and connect a hose from a compressed air cylinder to it.
6.4. It looks like an adapter to the air hose, which is screwed into the hole for the spark plug
Note. Most compression gauges are equipped with a screw-on adapter that fits into a quick-release air hose fitting.
5. Turn away a bolt, remove a support and a yoke of the valve and take a pusher bar (see section 5). If it is necessary to replace the cuffs on all the valve stems, then at the same time all valve rocker arms and valve tappets must also be replaced.
6. Direct a jet of compressed air into the cylinder. Valves must be held in place by air pressure. If the valve surfaces or their seats are in poor condition, the valves may not be held in place due to air leakage. In this case, see the procedure below.
7. If no compressed air source is available, another method can be used. Set the piston just short of TDC on the compression stroke by about 45°, 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 socket wrench, turn the crankshaft in the direction of rotation until you feel a slight resistance to turning.
8. Having stuffed rags into the holes of the cylinder head above and below the valves to prevent parts from falling out, compress the valve spring using a special tool. Using pliers or a magnet, remove the spring cotters (see illustration).
6.8. After compressing the valve spring, remove the cotters with a magnet (as shown) or pliers
Note. There are two types of valve spring compressors with the cylinder head not removed. One of them works on the principle of capturing the lower rings of the spring and pressing on the spring plate when turning the handle. The second device is a lever type; here the valve rocker bolt is used as a stop (see illustration). Both devices are quite effective.
9. After removing the spring cotters and valve spring, remove the cuff (see illustration).
6.9. Valve details: 1 - valve stem cotters, 2 - valve spring plate, 3 - valve spring, 4 - valve guide collar, 5 - cylinder head, 6 - valve
Note. If the air jet is not strong enough to hold the valves closed during this operation, the seat or valve seat may be damaged. In this case, the cylinder head must be removed for additional repair work.
10. Wrap rubber band around the top of the valve stem to prevent the valve from falling into the combustion chamber, then release the air pressure.
Note. If nylon cord was used instead of compressed air, rotate the crankshaft slightly in the opposite direction of normal rotation.
11. Check the valve stem for damage. Turning the valve in the guide, check it for eccentricity. The presence of eccentricity may indicate that the valve stem is bent.
12. Moving the valve in the guide up and down, check if it is sticking. The presence of sticking means that either the valve stem is bent or the valve guide is damaged. In both cases, you will have to remove the cylinder head for additional repairs.
13. Blow compressed air into the cylinder again to keep the valve closed, and wind the rubber band off the valve stem. If a nylon cord was used instead of an air jet, rotate the crankshaft in the working direction of rotation until slight resistance to rotation appears.
14. Coat the valve stem with a coat of engine oil and install a new guide bushing seal.
15. Install the spring over the valve.
16. Install the spring plate and compress the valve spring.
17. Place crackers in the top groove. To prevent them from falling out during assembly, place a small amount of grease in them (see illustration). Release the pressure of the tool on the spring, make sure that the spring cotters are in place.
6.17. Before installing, apply a drop of lubricant to each cracker, as shown here; this will hold them in place when installing the spring
18. Disconnect the air hose and unscrew the adapter from the spark plug hole. If a nylon cord was used instead of compressed air for this work, remove it from the cylinder.
19. Install the rocker arm and valve lifter rod.
20. Wrap the candles and connect the ignition wires to them.
21. Install the valve cover in accordance with section 4.
22. Start the engine and let it run for a while, then check for oil leaks or unusual noises coming from the valve cover area.