Lapping of valves and replacement of valve stem seals for cylinder head of diesel 740 Kamaz
If the valve does not sit tightly on the seat, then gaps form in some parts of the valve and seat
At the same time, gases under pressure and at high speed pass into the gaps formed, therefore, in this place, the chamfers are subjected to severe corrosion and the fit of the valve to the seat deteriorates.
Combustion products accumulate on the surface of the chamfer of the valve, as a result of which the tightness of the joint is broken.
Oil caps are replaced with increased oil consumption and with the next repair of cylinder heads.
Removing and grinding in valves
Remove the cylinder head, as described in the article - "How to replace the cylinder head gaskets of the 740 Kamaz diesel engine."
We install the cylinder head on a workbench or on the base of the I801.06.000 puller, if available.
If there is no such puller as in the picture (Fig. 1), then you can use a puller for VAZ cars (Fig. 2).
Before compressing the springs, we tap the spring plates with a hammer to make the locking crackers come out easier.
We compress the valve springs until the crackers completely come out of the bushing cone and remove the crackers.
Remove bushing 5 (Fig. 3), plate 7, springs 10 and 11, washer 13, and remove the valve.
Using tongs (Fig. 4) remove the valve stem seals.
We clean the valves and valve seats from carbon deposits and clean the rest of the parts in diesel fuel.
The angles of inclination of the working chamfers must be within the limits at the saddle = 44˚45′; valve 45˚30′.
These angles are set when the cylinder head and valve are rebuilt 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.
Graphite grease prevents the guide bushing from getting abrasive from the lapping paste into its holes and facilitates the rotation of the valve during lapping.
We put a device for lapping valves on the valve stem (or, with some interference, a rubber tube to connect the valve to a reversible drill).
We apply a uniform thin layer of lapping paste on the working surface of the valve chamfer.
Turning on the drill at the minimum speed (in reverse mode) or rotating the device (in the case of manual grinding) alternately in both directions by half a turn, we grind the valve, periodically pressing it against the seat, then weakening the pressing force.< /p>
We continue grinding until a uniform matte belt 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 it with compressed air and check the quality of grinding.
To check the quality of grinding, apply with a soft pencil across the chamfer of the valve at an equal distance six to eight dashes, insert the valve into the seat and, pressing hard, turn it a quarter of a turn. If all the lines are erased, then the valve is well ground.
Cylinder head assembly
We insert the valves into the guide bushings, lubricating them with engine oil. We install washers 13 (Fig. 3).
Using the tool (Fig. 6), we press in the valve stem seals.
We install the springs, spring plates and, after compressing the springs, insert the locking crackers.
After installing the cotters and removing the valve spring compressor, apply a few light blows with a hammer on the end of the valve stem so that the cotters are guaranteed to be fixed in the groove of the stem.
If the skewed crackers remain unfixed, when the engine is started, the “dry” valve will fall into the cylinder, which will lead to a serious engine failure.
Check the tightness of the valves. We lay the head with the combustion chambers up, and pour a little kerosene up the shoulder into the chamber combustion.
If kerosene does not seep into the head channel within 3 minutes, then the valve is tight.
When kerosene leaks, lightly tap the end of the valve with a rubber mallet. If the leakage is not eliminated, we grind the valves again.
