Valve knock
Its frequency is less than the frequency of the knock of the crankshaft bearings, since the valves are driven by the camshaft
Causes of the malfunction and how to fix it:
- increased clearances between the distribution cams and shims. Check and adjust gaps;
- wear of the camshaft cams, wear of the valve guide or valve stem. Contact a service station to check and replace worn parts;
- broken valve spring. Check and replace spring.
Lack of valve tightness
Low compression in cylinders (compression check see chapter «The main malfunctions of the crank mechanism»).
Causes of malfunction and solutions:
- no gap (or insufficient clearance) between the camshaft lobes and shims. Check and adjust gaps;
- poor fit of valves to the seats. To check and eliminate this malfunction, it is better to contact a service station, as it will require removal of the cylinder head and, possibly, lapping or replacement of valves. The tightness of the valves is checked by pouring kerosene into the inlet and outlet channels of the cylinder head. At the same time, no leakage of kerosene from under the valves should be observed for 3 minutes.
If the valves are leaking, they must be lapped to the seats. Valves that are damaged, showing metal chipping or pitting on the face, should be replaced. Lappe the valves to the seats with lapping paste. During lapping, 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.
Cylinder head cooling jacket leaking
There is a hit of coolant in the oil or, conversely, oil in the coolant. If the cylinder block is checked (see chapter «The main malfunctions of the crank mechanism») and 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 shells in the walls of the cylinder head cooling jacket.
To check the tightness, the holes of the cooling jacket are closed with plugs with gaskets. For example, the bottom holes can be covered with a solid steel plate bolted through the cylinder head bolt holes. Close the holes for the passage of liquid to the inlet pipeline also with steel plates, fixing them on the studs of the exhaust manifold. And instead of the outlet pipe of the cooling jacket, install a special fitting and supply water through it at a pressure of 5 kgf / cm2. Within 2 minutes there should be no leakage of water from the cylinder head.
You can check the tightness of the cylinder head and compressed air. To do this, it is also necessary to close the holes of the cooling jacket 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 apply compressed air inside the cylinder head at a pressure of 1.5... 2 kgf / cm2. Within 1... 1.5 minutes, air etching from the cylinder head should not be observed.
A cylinder head with a leaky cooling jacket must be replaced.