Electrical PM

John Baxter | February 01, 2012

• Inspect all wiring for cracked or frayed insulation or rubbing against other parts. Repair bad wiring and protect it by using ties to keep it away from surrounding surfaces.

Alternator cooling system and belt maintenance

This Volvo D16 has a typical serpentine belt setup. To remove the belt, turn the tensioner, which is behind the alternator, counter-clockwise. Small cracks in belt grooves indicate a need for replacement.

Your alternator has a cooling system – a fan that forces air through passages in the windings. This airflow keeps resistance low enough for good output, and protects perishable insulation and internal connections unless threatened by dirty fan blades or clogged passages, Purkey says. The problem with the alternator’s location is that small oil leaks are common in the engine compartment. The dust sticks to the layer of oil, eventually coating the fan blades and possibly clogging the cooling passages.

If you see oil on the alternator, trace it back to the source and fix the leak. Then carefully clean the fan blades and air inlets in the body of the alternator with a clean rag to restore airflow.

Since the diesel is the truck’s ultimate source of power, it’s important to keep the belt system that spins the alternator in tip-top condition. Since belts depend on tension for the friction that makes them effective, check the tensioning mechanism and the alternator’s mounting system.

Testing belts and mounting system

1.  Put a wrench on each alternator mounting bolt and on any adjustable bolts that allow belt tension to be adjusted to make sure every bolt is snug. Also, look at the alignment of the pulleys to make sure the alternator and any tensioner or crankshaft pulley grooves are straight across from one another. If the back of the belt bends sideways in either direction as it comes out of the pulley groove, either the accessory itself or some other part of the system is loose or has a bent bracket or one of incorrect design. Distorted or incorrect brackets need to be replaced, as do missing bolts.

2.  Inspect each belt, looking for cracks on either the outside band or inside where the belt rides in the groove. Look carefully at the friction surface on either side of the V-shaped area. If there is any sign of cracks, or if these two surfaces are smooth from slippage, known as “glazing,” the belt should be replaced. Where serpentine belts that run around several accessories are used, check for the same kinds of cracks and glazing, plus for fraying that starts at the outside edges and works its way toward the center. Also, check to see the belt is clean and dry. If it is oil-soaked, replace it and fix the oil leak. Replace pulleys that are so old they have grooves in them where the belts ride.

3.  Test the tension of all belts that are manually adjustable with a tension gauge. You can look up required tension in your owner’s manual. Experienced do-it-yourself technicians can test tension with a thumb. You should be able to depress the belt a half-inch to three-quarters of an inch for each 10-inch span between pulleys. The belt should be snug, but slightly springy – not rock solid. Adjust the tension if necessary by loosening mounting and adjusting bolts, rotating the accessory with a socket drive to get the right tension, then retightening the bolts.

4.  If the accessories are driven by a serpentine belt, the system will have an automatic tensioner. Check to make sure the tensioner’s indicator line sits between the two lines nearby on the block. If the indicator is outside the other two lines, then either the tensioner is weak or the wrong-size belt has been installed. Either condition makes it impossible for the tensioner to do its job. If there is some tension on the belt but the indicator is not where it should be, replace the belt with one of the correct length.

5.  To check the tensioner itself, turn it away from the belt with a socket drive to remove tension, then disconnect the belt. Now use the drive to slowly rotate the tensioner from its neutral position all the way inward. If you feel any roughness or excessive friction, the tensioner’s damper is worn and the unit should be replaced. Replace the belt and start the engine. If the tensioner is working properly, the belt will operate smoothly. If the belt vibrates and the tensioner does not remain in a relatively stable position, this is another sign the tensioner’s damper is worn and should be replaced.

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