TROUBLESHOOTING GASOLINE ENGINES
TROUBLESHOOTING GASOLINE ENGINES
The troubleshooting procedures used for a marine gasoline engine are, in many ways, similar to those for a diesel engine. The two types of engines are quite similar with two exceptions, the manner of getting fuel and air into the cylinders and the method of ignition. This section deals primarily with the systems that differ in the gasoline and diesel engines. In addition, troubleshooting information is given on the electrical systems.
Even though most electrical maintenance and repair is the responsibility of an Electrician’s Mate, you, as an Engineman, can reduce the amount of electrical troubles by following the correct operating procedures. Most electrical system troubles develop from improper use, care, or maintenance.
The following information will help you detect electrical troubles and take corrective action. When a gasoline engine fails to start, one of three conditions exists. The engine is not free to turn, the starter does not crank the engine, or the engine cranks but does not start. Figure 3-44 lists many of the conditions and sources of such difficulties, If the engine will not turn over, some part is probably seized In this case you should make a through inspection, which may necessarily include some disassembly.
STARTER DOES NOT RUN
If the starter fails to turn, the trouble can usually be traced to the battery, connections, switch, or starter motor.
Symptoms of battery trouble generally occur before the charge gets too low to perform the required work Battery failure is normally preceded by a gradual decline in the strength of the battery charge. A dead battery may be the result of insufficient charging, damaged plates, or improper starting technique.
The generator, used to maintain the charge of the starting battery, may become defective. The normal symptoms are a low battery charge when the engine is started and a zero or low ammeter reading when the engine is running.
The battery must be in good condition to ensure the proper operation of the ignition system. A starter draws a heavy current from the best of batteries. When the battery is weak, it will be unable to operate the ignition system satisfactorily for starting because the heavy starting current will drop the voltage to an extremely low value.
NOTE: Keep flames and sparks of all kinds away from the vicinity of storage batteries. A certain amount of hydrogen gas is given off from a battery at all times. In confined spaces this gas can form a dangerous explosive mixture.
When you use tools around a battery, be careful not to short circuit the battery terminals. Never use a tool or metal object to make a so-called test of a storage battery. Keep batteries in exposed locations subject to low temperatures fully charged during cold weather. In extreme cold weather, remove storage batteries and place them in a warm compartment, if possible. Electrical connections are another possible source of trouble if the starter does not turn. All connections must be tight and free from corrosion to provide maximum voltage and amperage from the battery. Battery terminals, since they are more vulnerable to corrosion, looseness, and burning, are the principal sources of trouble.
Burned battery terminals may be caused by a loose connection, a corroded terminal, or a short circuit. Burning of terminals usually occurs when an engine is being started Burning may be indicated by such things as smoke, a flash, or a spattering of molten metal in the vicinity of the battery. Usually, the starting motor will cease to turn after these symptoms appear.
Switches, electrical relays, or contactors that are defective or inoperative may be the reason a starter will not turn. Contactors, being subject to extremely high current, must be maintained in the best possible condition. Starting contactors are either manually or magnetically operated and are designed to be operated for only short periods of time.
Starter motor troubles can be traced for the most part to the commutator, brushes, or insulation. If motors are to function properly, they must be kept clean and dry. Dirt and moisture make good commutation impossible. Dirty and fouled starter motors may be caused by failure to replace the cover band, by water leakage, or by excess lubrication.
Most starter motors have a cover to protect the commutator and windings. If you neglect to replace the cover or remove it as an aid to ventilation and cooling, dirt and water are sure to damage the equipment. Although lubrication of bearings is essential for proper operation, excessive lubrication may lead to trouble in a starter motor. Excess lubricant in the shaft bearings may leak or be forced past the seal and foul the insulating material, commutator, and brushes. The lubricant prevents a good electrical contact between the brushes and the commutator, causing the commutator to spark and heat and the brushes to burn.
Burned brushes are another possible source of trouble if the starter motor is inoperative. Burning may be caused by loose brush holders, improper brush spring tension, a brush stuck in the holder, a dirty commutator, improper brush seating surface, or overloading the starter.
