How is the lapping done?

What is compression? This is the pressure in the combustion chamber at the end of the compression stroke. It can be vented through the piston rings or through the valve mechanism. In the first case, repair involves only replacement, and in the second - it is quite possible to do without it. Let's consider such situations on an example of engine VAZ.

First of all, it is worth saying that this procedure is called "lapping valves". In the process of operation, a deposit is formed on the valve seats, which prevents them from completely closing. Thus, grinding the valves avoids this malfunction. How to determine that they need lapping? The answer is simple. If the compression in the cylinders has fallen, then such an operation is simply necessary. The fact is that the lapping of valves is needed for such engines, the resource of which has already been exhausted, and the unit is far from full.

Initially, a gap is formed between the seat and the valve seat due to the wear of the latter. Since the "cotton" when closing is quite strong, over time the edge is knocked down and the geometry of the fit is broken. Then the unburned mixture enters the gap, which simply cokes at the valve belts, which makes the gap even more. As a rule, such problems occur mainly with exhaust valves, since the inlet valves are "ground" by incoming flows. In addition, there are no obstacles to the flow of air, and at the time when the temperature is as high as possible, the valves are in a closed state.

Now directly about how the lapping of the valves is done. The WHA categorically prohibits owners of these cars from grinding the drill. According to them, it is impossible to make the right effort. But the fact is that effort is just not required. If it is applied, the saddle is uneven. In this case, the valve will be inaccurately centered, which will result in a gap on one side. This is fraught with the above-described consequences. But grinding the valves with a drill can not be as effective as possible with a special kit.

It is produced in three stages. Their order depends on the granularity of the lapping paste, which varies in the process. If the lapping of the valves is done by a drill, then a pin of the same diameter as the rod is clamped into it. One end of the hose is put on this pin, and the other on the valve. Then the saddle and belt are greased with paste, after which a small rotation speed is set. If they are too small, it's not terrible - the operating time will increase slightly.

If they are large, there is a risk of overheating both the saddles and the valves. Then they will have a characteristic blue strip. This is a sure sign of overheating. After the initial treatment, the paste is rubbed off, then the next, less granularity is rubbed. After applying the third paste, the surfaces are thoroughly wiped with kerosene. Then you need to lubricate them with engine oil and repeat the lapping procedure, observing the "high-speed mode". This will ensure maximum tight closure.

Well, after that, the compression in the cylinders will increase noticeably. It should be remembered that engines whose compression ratio is less than 8 are very sensitive to it. This greatly affects the ease of operation, so grinding the valves can be carried out even between repairs, for example, after 20 000 km of run.