SPRING-DASHPOT 4N6410 - Caterpillar

All Industrial, Generator Set EnginesCaterpillar's specifications say that ground straps must be used on all installations of all Industrial and Generator Set Engines. Engine component damage is possible if an acceptable ground strap to the grounded battery terminal is not part of the engine's electrical system.
In some engine installations, the alternator is wired directly to an engine component such as a cylinder head or the cylinder block. If that component is not adequately connected to the ground terminal of the battery, current will pass through the engine components as part of the electrical system. This current can damage engine components.
Electrical Discharge Damage
When current passes between the crankshaft and the main bearings, microscopic pitting occurs on the main bearings and on the crankshaft journals. This pitting creates a rough surface on the journals. The rough surface acts as a very fine abrasive, slowly removing material from the main bearings until they are destroyed.
Although the pitting is not visible to the unaided eye, it collects bearing material which appears as streaks on the main journals. See Illustrations 1 and 2. When electrical discharge damage first begins, the streaks are short and randomly oriented as shown in Illustration 1. As the damage advances, the streaks become more uniform, that is, they become parallel and they extend all around the main journals. See Illustration 2.
Illustration 1. Early electrical discharge damage.Damaged main bearings will appear completely worn, but the wear normally is more advanced on the rear main bearings. See Illustration 3. There will be no indications of heat damage either on a bearing or on a journal unless a bearing has turned in its bore.
Illustration 2. Advanced electrical discharge damage.Rod journals and bearings generally show no damage unless a main bearing has turned in its bore and caused debris which flows in the oil to the rod bearings.
Prevention Of Electrical Discharge Damage
Electrical discharge damage can be prevented only by the use of an adequate ground. This ground must provide a good electrical connection between the engine block, the mounting rails, the legs and the grounded terminal on the battery. The ground strap for fixed installations must connect all components of the installation to the grounded battery terminal. To test the ground on a fixed installation, the serviceman should:
1. Start and run the engine at approximately 60 percent of the rated engine rpm.2. Turn on all electrically-powered accessories.3. Use a voltmeter to measure the voltage potential between the engine block or the rails or legs and the grounded battery terminal. The voltage will be less than .5 volt if the ground is adequate.
Illustration 3. Bearings destroyed by electrical discharge damage. Bearings are in sequence from left to right.