You will need: a micrometer, a caliper, a ruler
Remove carbon deposits from the combustion chambers
Pre-soak the carbon deposits with kerosene.
Mechanical cleaning of carbon deposits is possible. Be careful - avoid inhaling dust generated during cleaning of combustion chambers.
To prevent dust formation, periodically wet carbon deposits with kerosene
Inspect the head.
If there is a suspicion of cracks in the cylinder head (especially if coolant gets into the crankcase or oil gets into the coolant), check the tightness of the cylinder head on a special stand (in repair shops with the appropriate equipment).
Check the condition of the seats valves.
There should be no signs of wear, cavities, corrosion, etc. on the working chamfers of the seats.
The valve seats can be replaced in a specialized workshop.
Minor damage (small marks, scratches, etc.) can be removed by grinding the valves (see "How to grind the valves of the Niva Chevrolet cylinder head").
More significant valve seat defects are eliminated by grinding.
It is recommended to grind the seats in a specialized workshop, since this requires special tools and equipment.
Remove carbon deposits from the valves and inspect them.
Deformation of the valve stem and cracks on its plate are not allowed.
If there is damage, replace valve.
Check whether the working chamfer is excessively worn or damaged.
Grinding of the working chamfer of the valves is allowed (in repair shops with the appropriate equipment).
After grinding, the chamfer angle relative to the plate plane should be 45°30’ ±5’, and the thickness of the cylindrical part of the plate should be at least 0.5 mm.
In addition, the exhaust valve should retain the alloy layer applied to the chamfer.
Measure the diameters of the valve stems.
The stem diameter of all valves should be 7.985–8.000 mm.
Measure the diameter of the hole in the guide bushings, determine the clearance between the valve stems and bushings by calculation.
The inner diameter of the bushings should be:
- – for intake valves 8.022–8.040 mm;
- – for exhaust valves 8.029–8.047 mm.
It is permissible to determine the diameter with a gauge (pass/no-pass), as shown.
Mounting clearance for new bushings and valves:
- – for intake valves 0.022–0.055 mm;
- – for exhaust valves 0.029–0.062 mm.
The maximum permissible clearance (when worn) is 0.15 mm.
Replace the valve stem seals regardless of their condition.
Inspect the valve levers.
On the surfaces mating with the valve stem, with the camshaft cam and with the spherical end adjusting bolt, scoring and scratches are not allowed.
If there is damage, replace the levers.
Inspect the valve springs.
Cracks and loss of elasticity of the springs are not allowed.
Replace the springs if necessary.
If possible, determine the elasticity of the springs by their deformation under load.
According to the technical requirements for the outer spring:
- – height in a free state 50 mm;
- – height under load 283.39±14.7 N (28.9±1.5 kgf) – 33.7 mm;
- – height under load 452.06±22.55 N (46.1±2.3 kgf) – 24 mm.
For the inner spring:
- – free height 39.2 mm;
- – height under load 136.30±6.86 N (13.9±0.7 kgf) – 29.7 mm;
- – height under load 275.55±13.73 N (28.1±1.4 kgf) – 20 mm.
Clean the mating surface of the head from the remains gaskets and check the flatness of this surface.
To do this, place a metal ruler with its edge on the surface of the head in the middle along the axis of the head, and then measure the gap between the plane of the head and the ruler diagonally and with a feeler gauge.
Replace the head if the gap exceeds 0.1 mm.
Always replace the cylinder head gasket with a new one, since a gasket removed from the engine, even if it is not damaged externally, may be heavily compressed and will not provide seal tightness.
