Sooner or later, any engine becomes a source of trouble: it stalls on the road, doesn't want to start in the morning, pulls worse, "eats" excess fuel and oil. It is quite possible that the reason for its capricious behavior is simple: it is enough to clean the carburetor, adjust the ignition and replace the oil seals for everything to return to normal. But it happens that traditional approaches do not help him, and when measuring the compression it turns out that in one or several cylinders it is below the permissible level - and the issue becomes serious.
Then, first of all, the nature of the malfunction is clarified: wear of the cylinder-piston group, burning of the valve chamfers, or wear of the rods and guide bushings. The diagnostic technique is quite simple and is described in all engine repair manuals.
Then they decide on the repairs. Here you just need to make it a rule: stay away from any miraculous 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 treats engines is no longer difficult today, and not only in large cities. But how is the work organized there, what is its quality? Life shows that, despite the importance of experience and qualifications of employees, good results are unattainable without special equipment and gear, and in this regard, the range of technical equipment of our stations and mechanics is, alas, large. And if what was said above mainly concerned the motorist-operator, then the further presentation is addressed not so much to him as to the mechanic, because we will talk about technology.
In cases where the diagnostic test results indicate a valve mechanism fault, the cylinder head must be removed. The first step after dismantling, disassembling and general inspection is to assess the clearances between the valve stems and their guide bushings. If they are higher than the maximum permissible values, the valves are replaced with new ones. But when this half-measure is not enough, the bushings have to be replaced too.
For a small workshop, such an operation presents certain difficulties: cast iron bushings are pressed into an aluminum body with tension. To avoid microcracks and crushing, the bushings must be pre-cooled in liquid nitrogen (temperature - 196°C), and the housing must be heated to 160-170°C (above may cause harmful effects). All this is quite complicated, labor-intensive and often simply not reproducible in semi-artisanal conditions. Therefore, in rare workshops they do not deviate from the prescribed conditions, which directly results in a loss of fit quality and distortion of the geometry of the unit. It is then corrected by processing the valve seats "on site" with a countersink or a burr, and the valves themselves are lapped in a long and tedious process.
But today there is another method that is highly cost-effective both in terms of labor intensity and investment, while guaranteeing high-quality results. It is achieved by using the original and almost unknown in our practice tool of the American company "Neway" (Neway).
With its help, worn guide bushings are restored on-site, without pressing out! Special roller knives cause plastic deformation of the metal, compensating for wear on the inner surface of the bushing, 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 task of oil scraper caps.
The kit includes five knives and a set of reamers for finishing the bushing. It is characteristic that all operations with the Neway instrument are carried out manually and are not connected with electricity supply or other energy from outside.
Now about the valve seats. With traditional methods of processing them, the guide of the roller or countersink rotates freely in the valve sleeve. The Neway milling cutters have a fixed axis, which is tightly fixed in the restored bushing by a self-adjusting expansion collet "pilot". The milling cutter is put on the axis with a precision clearance of 0.5 microns, which ensures a minimum processing tolerance. Due to the unique sharpening and shape of the cutting edges, Neway cutters form a special micro-relief of the "comb" type on the surface of the valve seat: the valve and seat are run in quickly and efficiently, and there is no 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. For this operation, the Neway company offers a special tool, the Gizmatik-2. The valve is fixed in a special device, which in turn is installed in a bench vice. A few turns of the cutter are enough (axial feed is provided by a microlift), to obtain a perfect concentric valve surface. Note that on its working surface, as in the processing of the saddle, a special microrelief is also formed.
Well, that's all. All that's left is to wash and lubricate all the parts, and you can assemble the head.
And what about lapping? Let us remind you once again: when working with the Neway tool, there is no need for this tedious, long and boring operation. After processing the valve-seat pair, the connection of both parts occurs along a very narrow belt, practically along a line.
This is achieved with a small (up to one degree) divergence of the angles of processing of the working surfaces of the seat and valve (between them a so-called interference angle is formed). In the first seconds of engine operation, the mating area increases due to the crushing 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 in the first month of operation, and when repairing foreign car engines, it can bring in a noticeable income.