Contents: Cylinder head ↓ Valve seats ↓ Valves ↓ Oil deflector caps of guide bushings ↓ Springs and pushers ↓ Adjusting washers, cylinder head…↓
Cylinder head
The cylinder head is thoroughly washed and the oil channels are cleaned. Carbon deposits are removed from the combustion chambers and from the surface of the exhaust channels with a metal brush.
Inspect the cylinder head. There should be no scoring or damage on the camshaft journal beds and in the valve tappet holes. Cracks in any places on the cylinder head are not allowed. If there is a suspicion of coolant getting into the oil, check the tightness of the cylinder head.
To check for leaks, close the cooling jacket openings with plugs and pump water under a pressure of 5 kgf/cm². No water leakage from the cylinder head should be observed within 2 minutes. The cylinder head leaks can be checked with compressed air, for which the cooling jacket openings are plugged with the plugs of device 67.7871.9510, the cylinder head is lowered into a bath of water heated to 60-80°C, and allowed to warm up for 5 minutes. Then compressed air is supplied into the head under a pressure of 1.5-2 kgf/cm². No air leakage from the cylinder head should be observed within 1-1.5 minutes.
Valve seats
On the working chamfers of the saddles (figure 46) there should be no pinholes, traces of corrosion or damage in the area of contact with the valves. If there are metal build-ups along the inner diameter of the seat, in the area of the working edge, they are removed with A.94092 cutters (for exhaust valve) and A. 94003 (for intake valve), maintaining the dimensions ∅ 27.6 and ∅ 31 mm. The cutters are placed on the spindle A.94058 and centered with the guide rods from the set A.94059.
Figure 46. Profile of seats and heads of intake (I) and exhaust (II) valves
Check the tightness of the valves, for which purpose carefully clean the seats and valves, install valves with springs in the cylinder head and pour kerosene into the inlet and outlet channels of the cylinder head. When left for 3 minutes, no kerosene leakage through the valves should be observed.
In case of leakage of valves, they are ground to the seats using grinding paste and a mandrel with a rubber suction cup or a special drill, turning the valve alternately in both directions. During grinding, it is recommended to install a release spring with low elasticity under the valve.
After lapping, thoroughly wash the seats and valves from the lapping paste and blow them out with compressed air.
Valves
Remove carbon deposits from the valves. Check to see if the stem is deformed (rod straightness no more than 0.015 mm) and whether there are any cracks on the valve head. The damaged valve is replaced.
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Check the condition of the valve working chamfer. In case of minor damage, it can be ground, maintaining the chamfer angle of 45°30'±5'. In this case, the distances from the lower plane of the valve head to the base diameters (∅ 34 and ∅ 30.5 mm) should be as shown in Figure 46.
Valve guides. Check the clearance between the guides and the valve stems by measuring the valve stem diameter and the guide bore. The clearance should match the data table 1. If the clearance is greater than the permissible value, replace the valve. If the excessive clearance is not eliminated by replacing the valve alone, replace the guide bushing as well. For this operation, use the A.60153/R* mandrel, pressing in the bushings with the retaining ring on until it rests against the cylinder head body.
* Step mandrel with diameter and length of 12.5 and 58 mm respectively. Centering shank diameter 7.75 mm.
Guide bushings are supplied as spare parts with an outer diameter increased by 0.02 mm and with an allowance for the inner diameter. Therefore, after pressing in, the holes in the guide bushings are reamed with reamers (A.90310/1 for inlet valve bushings and A.90310/2 for outlet valve bushings).
Then the valves are checked for leaks and, if necessary, the valves are ground to the seats.
Oil deflector caps of guide bushings
The oil deflector caps must not have rubber peeling off from the fittings, cracks or excessive wear of the working edge. When repairing the engine, it is recommended to always replace the oil deflector caps with new ones.
Damaged caps must be replaced on a removed cylinder head to avoid bending the valve stems. To press on the caps, use mandrel 41.7853.4016 (see figure 40).
Springs and pushers
The springs are checked for elasticity and cracks. The elasticity of the valve springs is checked by the length of the spring in a free state (44.7mm outer and 35.2mm inner) and under load: 26+1,9-1,5 and 47.4+2,5-2,3 kgf for external (in this case the length should be 33.7 and 24.7 mm respectively); 11 +1,1-0,7 and 29+1,6-1,4 kgf for internal (the length is 29.7 and 20.7 mm respectively).
Check the condition of the working surface of the pusher. It should not have any burrs or scratches. If damaged, replace the pusher.
Adjusting washers, cylinder head mounting bolts
The working surfaces of the washers must be smooth, without nicks, scratches and burrs. They must not have stepped or one-sided wear or metal rubbing. Concentric traces from running-in with the camshaft cams are allowed.
When using cylinder head bolts repeatedly, they stretch out. Therefore, check whether the bolt length does not exceed 135.5 mm (excluding the height of the bolt head), and if it is larger, then replace the bolt with a new one.