If the valve does not fit snugly against the seat, gaps will form in some areas of the valve and seat. In this case, gases under pressure and at high speed pass into the formed cracks, therefore, in this place the chamfers are subject to strong corrosion and the adhesion of the valve to the seat deteriorates.
Combustion products accumulate on the surface of the valve chamfer, as a result of which the tightness of the connection is broken.
We replace the valve stem seals with increased oil consumption and with the next repair of the cylinder heads.
Removing and lapping valves
We remove the cylinder head, as described in the article - "Replacing the cylinder head gaskets of the 740 Kamaz diesel engine".
We install the cylinder head on the workbench or on the base of the I801.06.000 puller, if available.
If there is no such a puller as in the picture (Fig. 1), then you can use a puller for VAZ cars (Fig. 2)
Before compressing the springs, tap the spring plates with a hammer to make it easier for the locking crackers to come out.
Compress the valve springs until the crackers come out of the bushing cone completely and remove the crackers
Remove the sleeve 5 (Fig. 3), plate 7, springs 10 and 11, washer 13, and take out the valve.
Using pliers (Fig. 4), remove the valve stem seals.
We clean the valve and valve seats from carbon deposits and clean the rest of the parts in diesel fuel.
The angles of inclination of the working chamfers should be within the limits of the saddle = 44˚45 ′; at the valve 45˚30 '. These angles are set when restoring the cylinder head and valve before lapping.
We put a pre-selected spring on the valve stem (Fig. 5) and insert the valve into the guide sleeve from the side of the combustion chamber, lubricating the valve stem with a layer of graphite grease.
The graphite grease prevents abrasive from the lapping paste from getting into the guide bore holes and facilitates the rotation of the valve during lapping.
We put on the valve stem a device for grinding the valves (or with some tightness a rubber tube to connect the valve with a reversible drill).
Apply a uniform thin layer of lapping paste to the working surface of the valve chamfer.
Turning on the drill at the minimum rotational speed (in reverse mode) or rotating the device (in the case of manual lapping) alternately in both directions by half a turn, we grind the valve, periodically pressing it against the saddle, then weakening the pressing force.
We continue grinding until a uniform matte band with a width of at least 1.5 mm appears on the chamfers of the valves and seats.
We wash the valve seats and valves in diesel fuel, blow them with compressed air and check the quality of lapping
To check the quality of lapping, apply six to eight dashes with a soft pencil across the valve chamfer at an equal distance, insert the valve into the seat and, pressing firmly, turn it a quarter of a turn. If all lines are worn out, then the valve is worn well.
Cylinder head assembly
We insert the valves into the guide bushings, lubricating them with engine oil. Install washers 13 (Fig. 3).
Using the tool (Fig. 6), press in the valve stem seals.
We install the springs, spring plates and, compressing the springs, insert the locking crackers.
After installing the crackers and removing the valve spring compressor, apply a few gentle blows with a hammer to the end of the valve stem so that the crackers are guaranteed to be fixed in the groove in the stem.
If the skewed crackers are left unsecured, when the engine is started, the "dry" valve will fall into the cylinder, which will lead to a serious engine accident.
We check the tightness of the valves. We put the head with the combustion chambers up, and pour a little kerosene along the shoulder into the combustion chamber
If, within 3 minutes, kerosene does not seep into the head channel, the valve is sealed.
When kerosene leaks, we lightly tap with a rubber hammer on the end of the valve. If the leakage persists, we rub the valves again.