Valve knocking
Its frequency is lower than the knocking frequency of the crankshaft bearings, since the valves are driven by the camshaft
Causes of the malfunction and ways to eliminate it:
- increased clearances between the cams of the distribution hall and the adjusting washers. Check and adjust the clearances;
- camshaft lobes worn, valve guide or valve stem worn. Contact a service station to check and replace worn parts;
- valve spring failure. Check and replace the spring.
Lack of valve tightness
Low compression in the cylinders (for checking compression, see chapter "Main faults of the crank mechanism").
Causes of malfunction and methods of elimination:
- no gap (or insufficient clearance) between the camshaft cams and the adjusting washers. Check and adjust the clearances;
- poor valve fit to the seats. To check and fix this problem, it is better to contact a service station, as it will require removing the cylinder head and possibly grinding or replacing the valves. The tightness of the valves is checked by pouring kerosene into the inlet and outlet channels of the cylinder head. In this case, no kerosene leakage from under the valves should be observed within 3 minutes.
If the valves are not tight, they must be ground to the seats. Damaged valves with chipped metal or cavities on the working chamfer must be replaced. The valves are ground to the seats using a grinding paste. During grinding, it is recommended to install a release spring with low elasticity under the valve, and turn the valve alternately in both directions with a mandrel with a rubber suction cup, fixed, for example, in a brace.
The cylinder head cooling jacket is leaking
There is evidence of coolant getting into the oil or, conversely, oil getting into the coolant. If the cylinder block has been checked (see chapter "Main faults of the crank mechanism") and is intact, it is necessary to check the tightness of the cylinder head at a service station. It is possible that there are cracks, porosity or cavities in the walls of the cooling jacket of the cylinder head.
To check the tightness, the cooling jacket openings are closed with plugs and gaskets. For example, the lower openings can be closed with a solid steel plate, securing it with bolts through the openings for the cylinder head mounting bolts. The openings for the passage of liquid to the intake manifold are also closed with steel plates, securing them to the exhaust manifold mounting studs. And instead of the cooling jacket outlet pipe, install a special nipple and supply water through it under a pressure of 5 kgf/cm². There should be no water leakage from the cylinder head for 2 minutes.
The tightness of the cylinder head can also be checked with compressed air. To do this, it is also necessary to close the cooling jacket openings with plugs, lower the cylinder head into a bath with water heated to 60...80°C, and warm the cylinder head in the bath for 5 minutes. Then supply compressed air under a pressure of 1.5...2 kgf/cm² into the cylinder head. No air leakage from the cylinder head should be observed for 1...1.5 minutes.
A cylinder head with a leaky cooling jacket must be replaced.