If the valve does not seat tightly on its seat, clearances form on some areas of the valve and the seat.
The gases then pass under pressure and at high velocity into the gaps formed, so in that place the chamfers are subject to severe corrosion and the seating of the valve on its seat deteriorates.
Combustion products accumulate on the surface of the valve chamfer, as a result of which the tightness of the joint is impaired.
The oil-deflector caps are replaced when oil consumption increases and during the next overhaul of the cylinder heads.
Removal and grinding-in of valves
We remove the cylinder head as described in the article — “Replacement of the cylinder head gaskets of the 740 diesel engine”.
We place the cylinder head on the 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), a puller for VAZ cars can be used (Fig. 2).
- Before compressing the springs, we tap with a small hammer on the spring retainers so that the split collets come out more easily.
- We compress the valve springs until the collets come fully out of the bush cone and remove the collets.
- We remove bush 5 (Fig. 3), retainer 7, springs 10 and 11, washer 13, and withdraw the valves.
- Using the pliers (Fig. 4), we extract the oil-deflector caps.
- We clean the valves and valve seats of carbon deposits and clean the remaining parts in diesel fuel.
The inclination angles of the working chamfers must be within: at the seat = 44°45′; at the valve 45°30′. These angles are set during the restoration of the cylinder head and valve before grinding-in.
- We fit a pre-selected spring onto the valve stem (Fig. 5) and insert the valve into the guide bush from the combustion chamber side, having smeared the valve stem with a layer of graphite grease. The graphite grease protects the guide bush from abrasive from the grinding paste entering its holes and facilitates rotation of the valve during grinding-in.
- We fit onto the valve stem a valve grinding-in tool (or a rubber tube with some interference for connecting the valve to a reversible drill).
- We apply a uniform thin layer of grinding paste to the working surface of the valve chamfer.
- Switching the drill to the minimum speed (in reversible mode) or turning the tool (in the case of manual grinding-in) alternately half a turn in both directions, we grind in the valve, periodically now pressing it against the seat, now easing the pressing force.
- We continue grinding-in until a uniform matt band at least 1.5 mm wide 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 grinding-in.
To check the quality of grinding-in, we draw with a soft pencil across the valve chamfer at equal distances six to eight marks, insert the valve into the seat and, pressing hard, turn it a quarter of a revolution. If all the lines have been erased, the valve is well ground in.
Assembling the cylinder head
- We insert the valves into the guide bushes, having lubricated them with engine oil. We fit washers 13 (Fig. 3).
- Using the tool (Fig. 6), we press in the oil-deflector caps.
- We fit the springs, the spring retainers and, having compressed the springs, insert the split collets.
Important! After fitting the collets and removing the valve spring compressor, give a few light hammer blows on the end of the valve stem so that the collets are reliably fixed in the groove of the stem.
If collets fitted askew remain unfixed, when the engine is started the “de-colleted” valve will drop into the cylinder, which will lead to a serious engine failure.
- We check the tightness of the valves. We lay the head with the combustion chambers upwards and pour a little kerosene up to the collar into the combustion chamber.
- If within 3 min the kerosene does not seep into the channel of the head, the valve is tight.
- If kerosene leaks, we give light taps with a rubber hammer on the end of the valve. If the leak is not eliminated, we grind in the valves again.
