It is not unusual for one to hear an aviator complain that the engine he operates is not as responsive as it was when new after he has run it but relatively few hours. There does not seem to be anything actually wrong with the engine, yet it does not respond readily to the throttle and is apt to overheat. While these symptoms denote a rundown condition of the mechanism, the trouble is often due to nothing more serious than accumulations of carbon. The remedy is the removal of this matter out of place. The surest way of cleaning the inside of the motor thoroughly is to remove the cylinders, if these members are cast integrally with the head or of removing the head member if that is a separate casting, to expose all parts.
In certain forms of cylinders, especially those of the L form, it is possible to introduce simple scrapers down through the valve chamber cap holes and through the spark-plug hole if this component is placed in the cylinder in some position that communicates directly to the interior of the cylinder or to the piston top. No claim can be made for originality or novelty of this process as is has been used for many years on large stationary engines. The first step is to dismantle the inlet and exhaust piping and remove the valve caps and valves, although if the deposit is not extremely hard or present in large quantities one can often manipulate the scrapers in the valve cap openings without removing either the piping or the valves. Commencing with the first cylinder, the crank-shaft is turned till the piston is at the top of its stroke, then the scraper may be inserted, and the operation of removing the carbon started by drawing the tool toward the opening. As this is similar to a small hoe, the cutting edge will loosen some of the carbon and will draw it toward the opening. A swab is made of a piece of cloth or waste fastened at the end of a wire and well soaked in kerosene to clean out the cylinder.
When available, an electric motor with a length of flexible shaft and a small circular cleaning brush having wire bristles can be used in the interior of the engine. The electric motor need not be over one-eighth horsepower running 1,200 to 1,600 R. P. M., and the wire brush must, of course, be of such size that it can be easily inserted through the valve chamber cap. The flexible shaft permits one to reach nearly all parts of the cylinder interior without difficulty and the spreading out and flattening of the brush insures that considerable surface will be covered by that member.
BURNING OUT CARBON WITH OXYGEN
A process of recent development that gives very good results in removing carbon without disassembling the motor depends on the process of burning out that material by supplying oxygen to support the combustion and to make it energetic. A number of concerns are already offering apparatus to accomplish this work, and in fact any shop using an autogenous welding outfit may use the oxygen tank and reducing valve in connection with a simple special torch for burning the carbon. Results have demonstrated that there is little danger of damaging the motor parts, and that the cost of oxygen and labor is much lower than the old method of removing the cylinders and scraping the carbon out, as well as being very much quicker than the alternative process of using carbon solvent. The only drawback to this system is that there is no absolute insurance that every particle of carbon will be removed, as small protruding particles may be left at points that the flame does not reach and cause pre-ignition and consequent pounding, even after the oxygen treatment. It is generally known that carbon will burn in the presence of oxygen, which supports combustion of all materials, and this process takes advantage of this fact and causes the gas to be injected into the combustion chamber over a flame obtained by a match or wax taper.
Fig. 182.—Showing Where Carbon Deposits Collect in Engine Combustion Chamber, and How to Burn Them Out with the Aid of Oxygen. A—Special Torch. B—Torch Coupled to Oxygen Tank. C—Torch in Use.
It is suggested by those favoring this process that the night before the oxygen is to be used the engine be given a conventional kerosene treatment. A half tumbler full of this liquid or of denatured alcohol is to be poured into each cylinder and permitted to remain there over night. As a precaution against fire, the gasoline is shut off from the carburetor before the torch is inserted in the cylinder and the motor started so that the gasoline in the pipe and carburetor float chamber will be consumed. Work is done on one cylinder at a time. A note of caution was recently sounded by a prominent spark-plug manufacturer recommending that the igniter member be removed from the cylinder in order not to injure it by the heat developed. The outfits on the market consist of a special torch having a trigger controlled valve and a length of flexible tubing such as shown at [Fig. 182], A, and a regulating valve and oxygen tank as shown at B. The gauge should be made to register about twelve pounds pressure.
The method of operation is very simple and is outlined at C. The burner tube is placed in the cylinder and the trigger valve is opened and the oxygen permitted to circulate in the combustion chamber. A lighted match or wax taper is dropped in the chamber and the injector tube is moved around as much as possible so as to cover a large area. The carbon takes fire and burns briskly in the presence of the oxygen. The combustion of the carbon is accompanied by sparks and sometimes by flame if the deposit is of an oily nature. Once the carbon begins to burn the combustion continues without interruption as long as the oxygen flows into the cylinder. Full instructions accompany each outfit and the amount of pressure for which the regulator should be set depends upon the design of the torch and the amount of oxygen contained in the storage tank.