CHAPTER XIII
LOCATING TROUBLE
There are many ways in which an engine can give trouble, but these are not serious to an operator who understands the action of an engine, and who works with his brain as well as with his hands. Each of these troubles has a distinct cause; proper care will avoid them, but if they come the reasons for them can be determined by simple tests.
In order to develop full power, an engine must be in good mechanical condition; that is, the bearings must be free without being loose, the gears must run well, the pistons and their rings must not bind or be too free, and so on. It must be properly lubricated and cooled, compression must be correct, it must get a good mixture, and ignition must take place at the right time. If an engine gives trouble, it is because one of these systems is not working properly, and it is not at all difficult to locate the cause and to correct it.
If an engine gets a good mixture, which is ignited properly, it will run; if it will not give any explosions it is because one or the other of these systems is not working properly. An inspection or a simple test will show which one is at fault.
ENGINE WILL NOT START
If an engine will not start after being cranked a dozen or twenty times, it is useless to continue to crank it. It is not getting either a proper mixture or an ignition spark, and it saves time and energy to find out where the trouble is, rather than to keep on cranking in the hope that something may happen.
When a tractor engine refuses to start, the trouble is usually with the mixture, and, more often than not, this is due to carelessness or to forgetfulness. The tank may be empty, or the fuel valve may be closed, so that the carburetor is dry; see if there is fuel in the carburetor bowl. The engine may have been shut down while running on kerosene, instead of having been switched to gasoline for the last few minutes of its run, so that the carburetor, intake manifold and cylinders contain kerosene, which will not vaporize without heat, instead of gasoline, which will. In this case the engine must be primed with gasoline.
If too much gasoline has been used for priming, the cylinders may contain a mixture that is too rich to ignite; the engine should then be cranked briskly with the fuel shut off and the compression relief cocks open, to clear out the rich mixture and fill the cylinders with air.
Water in the fuel will make starting difficult or impossible. It is easy to forget to shut off the water valve of the carburetor when stopping the engine, and when starting, water from this valve will prevent the forming of a mixture and will also interfere with the ignition.
If the mixture is apparently all right, the fault may be in the ignition. A drop of liquid fuel or of water, for instance, may be on the spark plug points; this will short-circuit them and no spark will be formed, although the sparking current is passing.
If there is a suspicion that the ignition system is at fault, and that the magneto is not producing a sparking current, it should be tested, as explained in Chapter XII.
Starting in cold weather is always more difficult than starting when it is warm. Helps in cold weather starting are given in Chapter XI.
A leaky inlet manifold will admit an extra amount of air that will completely alter the proportions of a mixture. Thus the mixture will be wrong, although the carburetor adjustment seems to be correct. Manifold leaks are usually at the joints, but occasionally a manifold is found with a hole in it due to poor casting or material, or a crack may develop.
Difficulty in starting due to poor compression caused by stuck valves or rings will show its cause by the ease with which the engine can be cranked.
If an engine is free enough to turn over, poor lubrication or cooling will not interfere with starting it. Faults in these systems show themselves only when an engine is running.
ENGINE LOSES POWER
An engine will lose power through a defect of compression, carburetion, ignition, cooling or lubrication, or because of a mechanical fault.
If the trouble comes from cooling or lubrication, the engine will overheat and thus make the cause known. A bearing that binds will become very hot, while if the cooling system fails, the engine will be hot all over. When the engine is excessively hot, the pistons will expand, and much of the power of the engine will be used up in forcing them to move.
An engine that is not hotter than usual, and is having regular and even explosions, probably loses power through a loss of compression. This is the most usual cause of this trouble, and it is located and remedied as explained in Chapter XII.
If compression is good, the loss of power may be due to a clogged muffler or exhaust pipe, which will not permit the free escape of the burned gases. This condition will prevent full charges of fresh mixture from entering the cylinders, and the engine then cannot be expected to deliver full power.
Another possible cause of a loss of power with the engine apparently in proper condition is the sticking or poor adjustment of the governor. The factory adjustment of the governor should not be changed, however, until it is definitely proved that that is where the trouble lies.
If the engine misses fire, or runs irregularly, the loss of power will be due to faulty carburetion or ignition. The mixture may be too rich or too lean; in either case the trouble will be remedied by readjusting the carburetor. A mixture that is very much too lean will make itself known by backfiring; there will be little explosions at the carburetor. This should be remedied at once, for the danger of fire from it is very great. Black smoke at the exhaust is a sign of a mixture that is too rich.
An engine will not deliver full power if it is run on a retarded spark. A loss of power from this cause will be accompanied by general overheating of the engine.
ENGINE STOPS
The manner in which an engine stops will indicate the reason for it.
A failure of the ignition system that stops the formation of current, like the sticking of the circuit breaker lever, will cut off all explosions instantly; the engine will stop abruptly. An engine will not stop abruptly from any fault with the mixture; with mixture trouble the explosions will become weaker and weaker until they cease.
If an engine stops through a failure of the lubrication or cooling systems it will be intensely hot, which will not be the case if the fault is with carburetion or ignition.
A running engine will not be brought to a stop by a loss of compression.
ENGINE MISSES
A steady or irregular miss in one cylinder is usually due to the spark plug’s being cracked or dirty. Carburetor trouble will affect all the cylinders; it cannot affect one cylinder only, and missing in one cylinder may be put down as ignition trouble. In this case ignition trouble does not mean magneto trouble, for if the magneto produces sparking current for one cylinder it will produce it for all. Therefore ignition trouble in only one cylinder is in those parts of the ignition system supplying that cylinder; that is, in the spark plug or in the spark plug cable.
A less likely cause for missing in one cylinder only is poor compression. It is usually the case that if compression is poor in one cylinder it is poor in them all, but a broken valve or piston ring or a weak valve spring will weaken compression in one and not in the others.
A cylinder that misses is cooler than the others, and can be located by feeling. It can also be located by short-circuiting the spark plugs one at a time; this will make no difference in the dead cylinder, but when the spark plug of an active cylinder is short-circuited the speed of the engine will drop.
To short-circuit a spark plug, take a wooden-handled screwdriver or other tool and rest the blade on the engine near the spark plug; then tilt until its shank is close to the spark plug terminal. The spark current will then pass to the metal of the engine by way of the tool instead of by the spark plug points. This is also a test of ignition, for a spark will pass between the terminal and the tool.
Irregular missing in all cylinders may be due to a fault at one of the parts of the ignition system that supplies them all; a dirty distributor, for instance, or a sticking circuit breaker lever, or rough platinum points. It may also be due to a clogged fuel line, which prevents the carburetor from getting a regular and sufficient flow.
Irregular missing will also be caused by loose ignition connections, and by loose switch parts.
ENGINE STARTS; BUT STOPS
When an engine starts readily but quickly slows down and stops, the reason is almost always an insufficient supply of fuel. An obstruction in the pipe may prevent the fuel from flowing fast enough to keep the carburetor bowl filled when the engine is running; when the engine starts, the fuel is sucked out of the spray nozzle faster than it comes in through the float valve, so the carburetor is soon drained and the engine stops. The bowl then fills, only to be sucked dry again when the engine is next started.
This difficulty is caused by dirt in the fuel, which collects in the strainer or the fuel pipe. The strainer is so arranged that it may be easily drained and cleaned; to clear out the pipe, shut off the fuel at the tank, disconnect the pipe at both ends, and blow through it.
The strainer should be drained every day; it is sufficient to open the strainer drain cock for two or three seconds.
Most of the troubles due to dirt in the fuel will be avoided if the fuel is strained when filling the tank.
Another thing that will bring an engine to a stop is the clogging of the vent holes in the tank filler cap and in the top of the carburetor bowl. These holes should be clear, so that air can enter to replace the fuel that is used; if air cannot enter the fuel will not flow, and the tank is then said to be air-bound.
ENGINE OVERHEATS
An engine may overheat either because it produces more heat than the cooling system can take care of, or because the cooling system is not taking off all of the heat that it should.
Running an engine with the spark retarded will cause it to overheat; so will a failure of the lubrication and an obstruction to the passage of the exhaust gases.
If an engine has been taken down and overheats when it is reassembled, it may be that the magneto has been wrongly timed, and produces its spark too late. If an engine has been running properly but begins to overheat, the ignition cause will be the faulty setting of the spark control, or the slipping of the spark control rod.
When an engine is run on kerosene, the oil in the crankcase must be frequently drained off and replaced with fresh oil. The reason for this is that part of the kerosene that goes to the cylinders does not vaporize and burn, but works its way past the pistons and into the crankcase, where it thins the lubricating oil. As the oil thins, it loses its ability to lubricate, and the engine begins to overheat.
Anything that produces extra friction will cause overheating, as, for example, a wrist pin that works endways and rubs against the cylinder wall, or a tight bearing.
For a cooling system to work properly it must contain a full supply of water, the passages must be clear, sufficient air must pass through the radiator, and the pump must be in proper condition.
Hose connections will rot, and a strip of rubber may peel off the inside and be drawn across the passage; or if dirty water is used, the dirt may choke the fine radiator passages or other channels. If the radiator is covered with mud, air cannot get at the tubes to take the heat from the water that they contain.
A very usual cause of overheating is a slipping fan belt; an adjustment is provided by which the belt can be tightened when it works loose.
ENGINE SMOKES
Black smoke indicates that the mixture is too rich; blue smoke is a sign of too plentiful lubrication. Oil that is too thin, or that is of a poor grade, will cause smoking; good quality oil of the grade recommended by the manufacturer should always be used.
Broken piston rings, or rings stuck in their grooves, will be the cause of smoking because they will permit an excess of oil to pass by them.