Sooner or later, any engine becomes a source of trouble: it stalls on the way, does not want to start in the morning, pulls worse, «eating» excess fuel and oil. It is likely that the reason for his capricious behavior is simple: it is enough to clean the carburetor or injection nozzles, adjust the ignition and replace the valve stem seals so that everything goes back to normal. But it happens that traditional approaches to restoring engine performance do not help, and when measuring compression, it turns out that in one or more cylinders it is below the permissible level.
Then, first of all, the nature of the malfunction is clarified: wear of the cylinder-piston group, burning of the plates or wear of the rods and valve guides. The diagnostic technique is quite simple and is described in many engine repair manuals.
After that, they are determined with repairs. Here you just need to make it a rule to stay away from all sorts of miraculous liquids. The effect is in principle possible, but rarely achieved; the usual result is extra cost and hassle. It is better to immediately focus on a full repair procedure.
Today it is not difficult to find a workshop where engines are treated, and not only in large cities. But how is the work organized there and what is its quality? Life shows that despite the importance of experience and qualifications of employees, good work results are unattainable without special equipment and equipment, and in this regard, the spread of technical equipment of our service stations and mechanics, alas, is large. And if what was said above concerned mainly the motorist-exploiter, then what follows is addressed not so much to him as to the mechanic, because we will talk about technology.
In cases where the diagnostic results indicate a malfunction of the gas distribution mechanism, the cylinder head must be removed. The first thing to do after removal, disassembly and general inspection is to evaluate the clearances between the valve stems and guide bushings. If they are more than the maximum allowable, then the valves are replaced with new ones. But when this half-measure is insufficient, the bushings have to be replaced as well.
For a small workshop, such work presents already known difficulties: cast-iron bushings are pressed into an aluminum housing with an interference fit. In order to avoid microcracks and crushing, the bushings have to be pre-cooled in liquid nitrogen (whose temperature is –196°С), and heat the block head itself to 160–170°С (when heated to a higher temperature, harmful effects may occur). All this is quite difficult, time-consuming and often simply impossible to do in semi-handicraft conditions. Therefore, in rare workshops, they do not deviate from the conditions prescribed by the repair manual, which directly results in a loss of fit quality and distortion of the connection geometry. It is then corrected by processing «local» valve seats, and the valves themselves are lapped for a long time and tediously.
But today there is another technique that is highly cost-effective, both in terms of labor intensity and investment, which at the same time guarantees high-quality results. It is based on the use of an original and almost unknown in our practice tool from the American company Neway.
With its help, the restoration of worn guide bushings is carried out on site without pressing out. Special knife-rollers cause plastic deformation of the metal, compensating for wear on the inner surface of the sleeve, at the same time forming a spiral groove in it, which improves the lubrication conditions for the valve stem, and also serves as a kind of labyrinth seal that facilitates the work of 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 another type of energy from outside.
Now for the valve seats. With traditional methods of their processing, the guide of the cutter or countersink rotates freely in the valve sleeve. Neway milling cutters have a fixed axle, which is firmly fixed already in the rebuilt bushing by a self-aligning expansion collet. The cutter is put on the axis with a precision clearance of 0.5 microns, which ensures a minimum machining tolerance. Neway milling cutters, due to the unique sharpening and shape of the cutting edges, form a special microrelief of the type on the surface of the valve seat «comb»: valve and seat burn-in is fast and efficient, and there is no need for grinding. Their productivity is high: any chamfer on the valve seat is obtained in 3-4 turns of the tool.
The last stage is the restoration of the working chamfers of the valves themselves. Neway offers a special tool for this operation «Tismatic-2». The valve is motionlessly fixed in a special fixture, which, in turn, is installed in a conventional metalwork vise. A few turns of the cutter are enough (axial feed is provided by a microlift), to get a perfect concentric valve surface. Note that on its working surface, as in the processing of the saddle, a special microrelief is also formed.
That, in fact, is all. It remains only to rinse and lubricate all the parts, after which you can assemble the head.
And the rubbing? Once again, when working with the Neway tool, this tedious, long and tedious operation is not necessary. After processing a pair «seat valve» the pairing of both parts occurs along a very narrow belt, almost along a line.
This is achieved by small (up to 1°) discrepancy between the angles of processing 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 crushing of the surface protrusions of the created microrelief on the chamfers, and then the required 100% compaction occurs.
With the cost of a set of equipment about $400 (depending on configuration) Neway can pay off in the first month of work, and when repairing foreign car engines, it can also bring a significant income.