Contents: Cleaning ↓ Examination ↓
Cleaning
1. Remove the remains of the old gasket from the cylinder head.
2. Clean carbon deposits from combustion chambers, then wash the head in a suitable solvent.
3. Clean any carbon deposits from the valves, perhaps even using a wire brush.
Examination
Cylinder head
1. Carefully inspect the cylinder head for cracks and other damage. If cracks are present, the head must be replaced.
2. Using a metal ruler and feeler gauge, check the flatness of the mating surface of the cylinder head. If the non-flatness exceeds the permissible limits, it is necessary to regrind the head, while its height must correspond to the required values.
3. Check the condition of the valve seats. If they are burnt, worn or defective, they must be replaced. If the valve seat is slightly worn, they must be ground in. Check the valve guides for wear by inserting the valve stem into them and moving it to the side. The movement should be insignificant. If the movement is excessive, remove the valve and measure the diameter of the valve stem. Replace the valve if necessary. If the valve stem is not worn, the guide is worn and must be replaced. Replace the valve guides at a service station.
4. If the valve seats need to be reground, this operation must be performed after installing new valve guides.
Valves
1. Check each valve head for localized corrosion, burns, cracks, and general wear. Check the valve stem for wear and bending. Check the end of the valve stem for wear. If any defects are present, the valve must be replaced.
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2. Using a micrometer, measure the valve stem diameter at several points along the stem. Any significant difference in the readings indicates valve stem wear and a mandatory valve replacement.
3. Measure the valve disc edge width. If the valve disc edge width is less than the permissible limit, the valve must be replaced.
4. If the valves are in satisfactory condition, they should be inserted into their seats and lapped. If the valve plates or seats are badly worn, they should be machined or even replaced before lapping.
5. The valve grinding is performed as follows...
5a. place the cylinder head with the combustion chambers facing up on wooden blocks.
5b. Lubricate the lapping paste on the valve plate and valve seat. Install the valve in place and install the suction cup with the holder on the valve plate. Rotate the valve with the suction cup in different directions, lap the valve, and periodically lift the valve to redistribute the lapping paste.
5v. If a coarse lapping paste is used, lap until a uniform matte surface appears on the valve seat and valve. Then wipe off the paste composition used and repeat the lapping process with a fine paste.
5g. Rub in until a light matte grey colour appears.
5d. Carefully remove traces of lapping paste using a suitable solvent.
Valve elements
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1. Check the valve springs for signs of damage and measure the free length of the spring.
2. Install the springs with one of the ends on the frame, check the deviation of the spring axis from the vertical plane. If one of the springs is damaged, all springs in the set must be replaced.
3. Replace the valve stem seals regardless of their condition.