Aviation Engines Part 22

See if magnetos are bolted on tight and wired.

See if magneto cables are in good condition.

See if rocker arm tappets have a .020" clearance from valve stem when valve is seated.

See if tappet clamp screws are tight and cottered.

See if all gasoline, oil, water pipes and connections are in perfect condition.

Air on gas line should be tested for leaks.

Pump at least three pounds air pressure into gasoline tank.

After making sure that above rules have been observed, test compression of cylinders by turning propeller.

"DO NOT FORGET TO SHORT BOTH MAGNETOS"

Be sure all compression release and priming c.o.c.ks do not leak compression. If they do, replace same with a new one immediately, as this might cause premature firing.

Open priming c.o.c.ks and squirt some gasoline into each.

Close c.o.c.ks.

Open compression release c.o.c.ks.

Open throttle slightly.

If using Berling magnetos they should be three-quarters advanced.

If all the foregoing directions have been carefully followed, the engine is ready for starting.

In cranking engine either by starting crank, or propeller, it is essential to throw it over compression quickly.

Immediately upon starting, close compression release c.o.c.ks.

When engine is running, advance magnetos.

After it has warmed up, short one magneto and then the other, to be sure both magnetos and spark-plugs are firing properly. If there is a miss, the fouled plug must be located and cleaned. There is a possibility that the jets in the carburetor are stopped up. If this is the case, do not attempt to clean same with any sharp instrument. If this is done, it might change the opening in the jets, thus spoiling the adjustment. Jets and nozzles should be blown out with air or steam.

An open intake or exhaust valve, which might have become sluggish or stuck from carbon, might cause trouble. Be sure to remedy this at once by using a little coal-oil or kerosene on same, working the valve by hand until it becomes free. We recommend using graphite on valve stems mixed with oil to guard against sticking or undue wear.

INSTALLING ROTARY AND RADIAL CYLINDER ENGINES

[Ill.u.s.tration: Fig. 156.--Diagram Defining Installation of Gnome "Monosoupape" Motor in Tractor Biplane. Note Necessary Piping for Fuel, Oil, and Air Lines.]

When rotary engines are installed simple steel stamping or "spiders,"

are attached to the fuselage to hold the fixed crank-shaft. Inasmuch as the motor projects clear of the fuselage proper there is plenty of room back of the front spider plate to install the auxiliary parts such as the oil pump, air pump and ignition magneto and also the fuel and oil containers. The diagram given at Fig. 156 shows how a Gnome "monosoupape" engine is installed on the anchorage plates and it also outlines clearly the piping necessary to convey the oil and fuel and also the air-piping needed to put pressure on both fuel and oil tanks to insure positive supply of these liquids which may be carried in tanks placed lower than the motor in some installations. The diagram given at Figs. 157 and 158 shows other mountings of Gnome engines and are self-explanatory. The simple mounting possible when the Anzani ten-cylinder radial fixed type engine is used given at Fig. 159. The front end of the fuselage is provided with a substantial pressed steel plate having members projecting from it which may be bolted to the longerons. The bolts that hold the two halves of the crank-case together project through the steel plate and hold the engine securely to the front end of the fuselage.

[Ill.u.s.tration: Fig. 157.--Showing Two Methods of Placing Propeller on Gnome Rotary Motor.]

PRACTICAL HINTS TO LOCATE ENGINE TROUBLES

[Ill.u.s.tration: Fig. 158.--How Gnome Rotary Motor May Be Attached to Airplane Fuselage Members.]

One who is not thoroughly familiar with engine construction will seldom locate troubles by haphazard experimenting and it is only by a systematic search that the cause can be discovered and the defects eliminated. In this chapter the writer proposes to outline some of the most common power-plant troubles and to give sufficient advice to enable those who are not thoroughly informed to locate them by a logical process of elimination. The internal-combustion motor, which is the power plant of all gasoline automobiles as well as airplanes, is composed of a number of distinct groups, which in turn include distinct components. These various appliances are so closely related to each other that defective action of any one may interrupt the operation of the entire power plant. Some of the auxiliary groups are more necessary than others and the power plant will continue to operate for a time even after the failure of some important parts of some of the auxiliary groups. The gasoline engine in itself is a complete mechanism, but it is evident that it cannot deliver any power without some means of supplying gas to the cylinders and igniting the compressed gas charge after it has been compressed in the cylinders. From this it is patent that the ignition and carburetion systems are just as essential parts of the power plant as the piston, connecting rod, or cylinder of the motor.

The failure of either the carburetor or igniting means to function properly will be immediately apparent by faulty action of the power plant.

[Ill.u.s.tration: Fig. 159.--How Anzani Ten-Cylinder Radial Engine is Installed to Plate Securely Attached to Front End of Tractor Airplane Fuselage.]

To insure that the motor will continue to operate it is necessary to keep it from overheating by some form of cooling system and to supply oil to the moving parts to reduce friction. The cooling and lubrication groups are not so important as carburetion and ignition, as the engine would run for a limited period of time even should the cooling system fail or the oil supply cease. It would only be a few moments, however, before the engine would overheat if the cooling system was at fault, and the parts seize if the lubricating system should fail. Any derangement in the carburetor or ignition mechanism would manifest itself at once because the engine operation would be affected, but a defect in the cooling or oiling system would not be noticed so readily.

The careful aviator will always inspect the motor mechanism before starting on a trip of any consequence, and if inspection is carefully carried out and loose parts tightened it is seldom that irregular operation will be found due to actual breakage of any of the components of the mechanism. Deterioration due to natural causes matures slowly, and sufficient warning is always given when parts begin to wear so satisfactory repairs may be promptly made before serious derangement or failure is manifested.

A TYPICAL ENGINE STOPPAGE a.n.a.lYZED

Before describing the points that may fail in the various auxiliary systems it will be well to a.s.sume a typical case of engine failure and show the process of locating the trouble in a systematic manner by indicating the various steps which are in logical order and which could reasonably be followed. In any case of engine failure the ignition system, motor compression, and carburetor should be tested first. If the ignition system is functioning properly one should determine the amount of compression in all cylinders and if this is satisfactory the carbureting group should be tested. If the ignition system is working properly and there is a decided resistance in the cylinders when the propeller is turned, proving that there is good compression, one may suspect the carburetor.

[Ill.u.s.tration: Fig. 160.--Side Elevation of Thomas 135 Horse-Power Airplane Engine, Giving Important Dimensions.]

If the carburetor appears to be in good condition, the trouble may be caused by the ignition being out of time, which condition is possible when the magneto timing gear or coupling is attached to the armature shaft by a taper and nut retention instead of the more positive key or taper-pin fastening. It is possible that the inlet manifold may be broken or perforated, that the exhaust valve is stuck on its seat because of a broken or bent stem, broken or loose cam, or failure of the cam-shaft drive because the teeth are stripped from the engine shaft or cam-shaft gears; or because the key or other fastening on either gear has failed, allowing that member to turn independently of the shaft to which it normally is attached. The gasoline feed pipe may be clogged or broken, the fuel supply may be depleted, or the shut-off c.o.c.k in the gasoline line may have jarred closed. The gasoline filter may be filled with dirt or water which prevents pa.s.sage of the fuel.

[Ill.u.s.tration: Fig. 161.--Front Elevation of Thomas-Morse 135 Horse-Power Aeromotor, Showing Main Dimensions.]

The defects outlined above, except the failure of the gasoline supply, are very rare, and if the container is found to contain fuel and the pipe line to be clear to the carburetor, it is safe to a.s.sume the vaporizing device is at fault. If fuel continually runs out of the mixing chamber the carburetor is said to be flooded. This condition results from failure of the shut-off needle to seat properly or from a punctured hollow metal float or a gasoline-soaked cork float. It is possible that not enough gasoline is present in the float chamber. If the pa.s.sage controlled by the float-needle valve is clogged or if the float was badly out of adjustment, this contingency would be probable.

When the carburetor is examined, if the gasoline level appears to be at the proper height, one may suspect that a particle of lint, or dust, or fine scale, or rust from the gasoline tank has clogged the bore of the jet in the mixing chamber.

If the ignition system and carburetor appear to be in good working order, and the hand crank shows that there is no compression in one or more of the cylinders, it means some defect in the valve system. If the engine is a multiple-cylinder type and one finds poor compression in all of the cylinders it may be due to the rare defect of improper valve timing. This may be caused by a gear having altered its position on the cam-shaft or crank-shaft, because of a sheared key or pin having permitted the gear to turn about half of a revolution and then having caught and held the gear in place by a broken or jagged end so that cam-shaft would turn, but the valves open at the wrong time. If but one of the cylinders is at fault and the rest appear to have good compression the trouble may be due to a defective condition either inside or outside of that cylinder. The external parts may be inspected easily, so the following should be looked for: a broken valve, a warped valve-head, broken valve-springs, sticking or bent valve-stems, dirt under valve-seat, leak at valve-chamber cap or spark-plug gasket.

Defective priming c.o.c.k, cracked cylinder head (rarely occurs), leak through cracked spark-plug insulation, valve-plunger stuck in the guide, lack of clearance between valve-stem end and top of plunger caused by loose adjusting screw which has worked up and kept the valve from seating. The faulty compression may be due to defects inside the motor. The piston-head may be cracked (rarely occurs), piston rings may be broken, the slots in the piston rings may be in line, the rings may have lost their elasticity or have become gummed in the grooves of the piston, or the piston and cylinder walls may be badly scored by a loose wrist pin or by defective lubrication. If the motor is a type with a separate head it is possible the gasket or packing between the cylinder and combustion chamber may leak, either admitting water to the cylinder or allowing compression to escape.

[Ill.u.s.tration: Fig. 162.--Front and Side Elevations of Sturtevant Airplane Engine, Giving Princ.i.p.al Dimensions to Facilitate Installation.]

CONDITIONS THAT CAUSE FAILURE OF IGNITION SYSTEM

If the first test of the motor had showed that the compression was as it should be and that there were no serious mechanical defects and there was plenty of gasoline at the carburetor, this would have demonstrated that the ignition system was not functioning properly. If a battery is employed to supply current the first step is to take the spark-plugs out of the cylinders and test the system by turning over the engine by hand.

If there is no spark in any of the plugs, this may be considered a positive indication that there is a broken main current lead from the battery, a defective ground connection, a loose battery terminal, or a broken connector. If none of these conditions are present, it is safe to say that the battery is no longer capable of delivering current. While magneto ignition is generally used on airplane engines, there is apt to be some development of battery ignition, especially on engines equipped with electric self-starters which are now being experimented with. The spark-plugs may be short circuited by cracked insulation or carbon and oil deposits around the electrode. The secondary wires may be broken or have defective insulation which permits the current to ground to some metal part of the fuselage or motor. The electrodes of the spark-plug may be too far apart to permit a spark to overcome the resistance of the compressed gas, even if a spark jumps the air s.p.a.ce, when the plug is laid on the cylinder.

If magnetos are fitted as is usually the case at present and a spark is obtained between the points of the plug and that device or the wire leading to it from the magneto is in proper condition, the trouble is probably caused by the magneto being out of time. This may result if the driving gear is loose on the armature-shaft or crank-shaft, and is a rare occurrence. If no spark is produced at the plugs the secondary wire may be broken, the ground wire may make contact with some metallic portion of the cha.s.sis before it reaches the switch, the carbon collecting brushes may be broken or not making contact, the contact points of the make-and-break device may be out of adjustment, the wiring may be attached to wrong terminals, the distributor filled with metallic particles, carbon, dust or oil acc.u.mulations, the distributor contacts may not be making proper connection because of wear and there may be a more serious derangement, such as a burned out secondary winding or a punctured condenser.

If the motor runs intermittently, _i.e._, starts and runs only a few revolutions, aside from the conditions previously outlined, defective operation may be due to seizing between parts because of insufficient oil or deficient cooling, too much oil in the crank-case which fouls the cylinder after the crank-shaft has revolved a few turns, and derangements in the ignition or carburetion systems that may be easily remedied. There are a number of defective conditions which may exist in the ignition group, that will result in "skipping" or irregular operation and the following points should be considered first: weak source of current due to worn out dry cells or discharged storage batteries; weak magnets in magneto, or defective contacts at magneto; dirt in magneto distributor or poor contact at collecting brushes. Dirty or cracked insulator at spark-plug will cause short circuit and can only be detected by careful examination. The following points should also be checked over when the plug is inspected: Excessive s.p.a.ce between electrodes, points too close together, loose central electrodes, or loose point on plug body, soot or oil particles between electrodes, or on the surface of the insulator, cracked insulator, oil or water on outside of insulator. Short circuits in the condenser or internal wiring of induction coils or magnetos, which are fortunately not common, can seldom be remedied except at the factory where these devices were made.

If an engine stops suddenly and the defect is in the ignition system the trouble is usually never more serious than a broken or loose wire. This may be easily located by inspecting the wiring at the terminals.

Irregular operation or misfiring is harder to locate because the trouble can only be found after the many possible defective conditions have been checked over, one by one.

COMMON DEFECTS IN FUEL SYSTEMS