Sooner or later, any engine becomes a source of trouble: it stalls on the road, doesn't want to start in the morning, has poor performance, and eats up excess fuel and oil. It is quite possible that the reason for its capricious behavior is simple: it is enough to clean the carburetor or the injectors of the injection system, adjust the ignition and replace the valve stem seals for everything to return to normal. But sometimes traditional approaches to restoring engine performance do not help, and compression measurements reveal that the compression in one or more cylinders is below the permissible level.
Then, first of all, the nature of the malfunction is determined: wear of the cylinder-piston group, burning of the plates, or wear of the valve stems and guide bushings. The diagnostic technique is quite simple and is described in many engine repair manuals.
After this, they decide on the repair. Here you just need to make it a rule to stay away from any miracle liquids. The effect is possible in principle, but is rarely achieved; the usual result is extra costs and hassle. It is better to immediately focus on a full-fledged repair procedure.
Finding a workshop that repairs engines is no longer difficult, and not only in large cities. But how is the work organized there, and what is its quality? Experience shows that, despite the importance of employee experience and qualifications, good results are unattainable without specialized equipment and facilities. In this regard, the technical capabilities of our service stations and mechanics, unfortunately, vary widely. While the above primarily applies to the motorist/operator, what follows is addressed not so much to them as to the mechanic, as it concerns technology.
In cases where diagnostic results indicate a malfunction of the valve timing mechanism, the cylinder head must be removed. The first thing to do after removal, disassembly and general inspection is to assess the clearances between the valve stems and the guide bushings. If they are greater than the maximum permissible values, the valves are replaced with new ones. But when this half-measure is not enough, the bushings also have to be replaced.
For a small workshop, this type of work presents the already familiar difficulties: cast iron bushings are pressed into an aluminum housing with tension. To avoid microcracks and crushing, the bushings must be pre-cooled in liquid nitrogen (the temperature of which is -196°C), and the cylinder head itself must be heated to 160–170°C (heating to higher temperatures may cause harmful effects). All of this is quite complex, labor-intensive, and often simply impossible to accomplish in semi-artisanal conditions. Therefore, few workshops do not deviate from the conditions prescribed in the repair manual, which directly results in a loss of fit quality and distortion of the connection geometry. It is then corrected by processing the valve seats "on site", and the valves themselves are lapped in a long and tedious process.
But today there is another method that is highly cost-effective in terms of both labor intensity and investment, while guaranteeing high-quality results. It is based on the use of an original and almost unknown in our practice instrument from the American company Neway.
With its help, restoration of worn guide bushings is carried out on site without pressing out. Special roller knives cause plastic deformation of the metal, compensating for wear on the inner surface of the bushing, while simultaneously forming a spiral groove in it, which improves the lubrication conditions of the valve stem and also serves as a kind of labyrinth seal, facilitating the work of the valve stem seals.
The kit includes five knives and a set of reamers for finishing the bushing. It is characteristic that all operations with the Neway tool are carried out manually and are not connected with the power supply or the receipt of any other type of external energy.
Now about the valve seats. With traditional machining methods, the roller or countersink guide rotates freely in the valve sleeve. Neway cutters have a fixed axis, which is tightly fixed in the restored bushing by a self-aligning expansion collet clamp. The cutter is mounted on the axis with a precision clearance of 0.5 µm, which ensures minimal machining tolerance. Neway cutters, thanks to their unique sharpening and cutting edge shape, create a special "comb"-type microrelief on the valve seat surface: valve and seat bedding are quick and efficient, eliminating the need for lapping. Their productivity is high: any chamfer on the valve seat is obtained in 3–4 turns of the tool.
The final stage is the restoration of the working chamfers of the valves themselves. Neway offers a special tool, the "Tizmatic-2," for this operation. The valve is fixed in place in a special fixture, which is then mounted in a standard bench vice. A few turns of the cutter are enough (axial feed is provided by a microlift), to obtain a perfectly concentric valve surface. Note that on its working surface, as in the processing of the saddle, a special microrelief is also formed.
That's it, really. All that's left to do is clean and lubricate all the parts, after which you can reassemble the head.
And what about lapping? Let's reiterate: when working with Neway tools, this tedious, time-consuming, and tedious operation is completely unnecessary. After processing the valve-seat pair, the connection of both parts occurs along a very narrow belt, practically along a line.
This is achieved by a small (up to 1°) difference in the angles of the working surfaces of the seat and valve (a so-called interference angle is formed between them). In the first seconds of engine operation, the mating area increases due to the compression of the surface protrusions of the created microrelief on the chamfers, and then the required 100% compaction occurs.
With the cost of the equipment set being around $400 (depending on the configuration) Neway can pay for itself within the first month of operation, and when repairing foreign car engines, it can also generate significant income.