A tool for lapping valves with their own hands
How the valve mechanism of the car engine works
To delve into the peculiarities of using scrapers or countersinks for valve seats, you must first understand how the valve mechanism of the car engine works, as well as what can lead to the appearance of malfunctions in its work.
Each of the cylinders of any internal combustion engine (ICE) operates in conjunction with two valves, one of which is the intake valve and the other is the exhaust valve. Operation of the internal combustion engine is performed through repetitive processes (cycles). Each of these processes involves feeding a fuel mixture into the working cylinder. This occurs when the intake valve is opened. After it is closed and the fuel mixture burns down, the exhaust gases need to be ejected from the cylinder, which is accomplished by opening the exhaust valve. The inlet and outlet valves, when closed, must ensure that the working cylinder is hermetically sealed.
Internal combustion engine valve diagram
During engine operation, the valves are subjected to both significant mechanical stress and various effects of the corrosive environment in which they are operated:
To be able to withstand such severe stresses over a long period of time, the valves are made of a high-alloy steel alloy with a considerable amount of chromium and nickel in its chemical composition.
During operation, the valve seats wear to varying degrees
The valve structure consists of two main elements: the guide rod and the head, which can be flat, convex or tulip-shaped. The valve stem can be completely cylindrical or made with a shaped groove, which is necessary for a more reliable fixation of the spring.
The fact that the ICE valve mechanism has malfunctioned can be determined by several signs, the most obvious of which are:
- Decrease in engine power, which affects the speed characteristics of the car;
- Unstable operation of the internal combustion engine at any RPM;
- an unnatural knocking sound coming from the engine compartment of the vehicle;
- large amount of smoke coming out of the exhaust pipe.
The gap between the valve and its seat leads to the formation of carbon deposits, and subsequently to the valve seat burnout
If we talk about the most common ICE failures associated with its valve mechanism, they include:
- appearance of a gap between the cylinder block housing and the cylinder head, which is due to their loose contact with each other (this gap, formed for a number of reasons, leads to depressurization of the system);
- formation of coke and sludge where the valve is in contact with the cylinder block (such sludge prevents the valve from completely closing the cylinder, which also leads to depressurization of the system).
The valve seats are repaired with this tool. To determine whether it is necessary to use a burr, or you can do without it, you should inspect the seats. They can be covered with soot and cavities, but if the chamfers have a regular conical shape, you can immediately proceed to lapping, otherwise, if the chamfers are rounded or have a step on them, it is necessary to give them the correct form with the help of the roller.
Since the shape and size of the seats on different heads are different (for example, in the VAZ-2106 and VAZ-2109), you need to pick a suitable tool. The seats can be reworked by hand or, to save time, with a drill. To do this, the roller is inserted into the chuck like a drill bit, and the surface layer of the metal is removed as a result. The signal to the end of the depletion process is the appearance of a shining even circle, which corresponds to the shape of the valve disk.
On the video it is possible to see how the saddles are treated with the roller. ” alt=””
How to check the quality of work
The signal to the end is the appearance of an even strip of about one and a half millimeters wide. Then check that the valves are properly lapped. To do this, rinse off the residual paste and apply oil, and then lapping takes some more time. This will show the shells and scratches that have not been removed, if any. If there are no such circles, the work is finished.
It should be noted that during the operation of the engine, the valves will pass the process of lapping already without outside interference, so do not waste time to add the quality of lapping to the ideal. If you check the lapping with kerosene, the fuel fluid may leak a little from under the closed valve, but after the engine has been running for a few days, the leak tightness will be greatly improved.
Such operation as valve lapping is included in the list of works on engine overhaul. It is aimed at ensuring the tightest possible fit of the valve head to the seat, thereby reducing as much as possible the possibility of fuel leaking into the cylinders or exhaust gas bursting.
After long time of the car exploitation the valve bevel and valve seat surfaces get sooted, microcavities and burrs appear.
As a result, the contact patch between the surfaces decreases, the valve does not fit tightly to the seat, so it starts leaking and the engine compression decreases.
The valve lapping is used to remove carbon deposits, cavities and burrs, which restores the contact patch between the valve and the seat.
In addition to performing this operation as part of the overhaul, valve lapping is carried out in a number of other cases.
So, these works are carried out:
- If a valve or seats are burned;
- If the valve head is burned through;
- When replacing them in case of damage, in general, whenever there are problems with these elements.
How-To: Lap Valves (by hand and drill method explained)
The valve lapping process
First remove the head from the engine. Then the camshaft, shims or timing pads are removed from the cylinder head.
The next step is to deburr the valves. either a tool is used for this purpose, or they are knocked out with a spacer.
After that, the valve poppets and springs are removed. The valve itself is removed from the head to evaluate its condition and the condition of the seat.
If it shows no signs of burning and its stem is not bent, it is not necessary to change it, it is suitable for further use.
The seat should also be inspected for signs of burning. If there are traces of burning of the seat, its surface is first processed with a burr.
After confirming that the surfaces are free from burning, start the lapping process.
To do this, some paste is applied to the valve chamfer for the initial machining.
The valve is returned to its seat and the lapping tool is placed on the valve spindle. If it is homemade, the rubber tube on the stem should be clamped.
Then the valve is pressed against the seat with a device and the lapping begins.
To do this, the valve is turned 180 degrees by using the screwdriver., after that it is turned in the opposite direction. This is how the lapping operation is carried out.
It takes approx. 5-7 mins to burnish the surface with one type of paste. time.
Periodically the valve position is changed. i.e. it needs to be turned by about 90 deg. from the extreme lapping position, after which the lapping process would be continued by another 180° rotation. and retorquing.
It is not desirable to mechanize the process by using a drill with an attachment to the valve stem.
Drills usually have a high rotational speed, so there is a risk of overheating the seat and valve bevel when lapping.
In this case it is better to use an electric screwdriver. But the circular motion, which will be provided by a drill or an electric screwdriver, lapping is not recommended, this operation is better to perform by half-turn of the valve, followed by turning in the opposite direction, that is manual lapping.
After rough-paste lapping, the surfaces are carefully cleaned with a rag to remove any paste residue.
Then a finishing paste is applied to the valve bevel and the lapping process is repeated.
The successful result of the lapping is an even gray matte color of the lapped surfaces without any traces of shells or scratches.
This way all valves are lapped one by one on both inlet and outlet valves. There is no particular difference in which engine of the car this operation is performed on.
The process of lapping the valves is the same for VAZ-2106, VAZ-2109 and later models.
The difference in difficulty of these cars may be only the cylinder head removal process, preparation for lapping, and convenience of access to the valves because of the slightly different shapes of the cylinder head.