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Most diesel mechanics work on the engines of heavy trucks, such as those used in hauling freight over long distances, or in heavy industries such as construction and mining. Many are employed by companies that maintain their own fleet of vehicles. The diesel mechanic's main task is preventive maintenance to avoid breakdowns, but they also make engine repairs when necessary. Diesel mechanics also frequently perform maintenance on other nonengine components, such as brake systems, electronics, transmissions, and suspensions.
Through periodic maintenance, diesel mechanics keep vehicles or engines in good operating condition. They run through a checklist of standard maintenance tasks, such as changing oil and filters, checking cooling systems, and inspecting brakes and wheel bearings for wear. They make the appropriate repairs or adjustments and replace parts that are worn. Fuel injection units, fuel pumps, pistons, crankshafts, bushings, and bearings must be regularly removed, reconditioned, or replaced.
As more diesel engines rely on a variety of electronic components, mechanics have become more proficient in the basics of electronics. Previously technical functions in diesel equipment (both engine and nonengine parts) are being replaced by electronics, significantly altering the way mechanics perform maintenance and repairs. As new technology evolves, diesel mechanics may need additional training to use tools and computers to diagnose and correct problems with electronic parts. Employers generally provide this training.
Diesel engines are scheduled for periodic rebuilding usually every 18 months or 100,000 miles. Mechanics rely upon extensive records they keep on each engine to determine the extent of the rebuild. Records detail the maintenance and repair history that helps mechanics determine repair needs and prevent future breakdowns. Diesel mechanics use various specialty instruments to make precision measurements and diagnostics of each engine component. Micrometers and various gauges test for engine wear. Ohmmeters, ammeters, and voltmeters test electrical components. Dynamometers and oscilloscopes test overall engine operations.
Engine rebuilds usually require several mechanics, each specializing in a particular area. They use ordinary hand tools such as ratchets and sockets, screwdrivers, wrenches, and pliers; power tools such as pneumatic wrenches; welding and flame-cutting equipment; and machine tools like lathes and boring machines. Diesel mechanics typically supply their own hand tools at an investment of $6,000 to $25,000, depending upon their specialty. It is the employer's responsibility to furnish the larger power tools, engine analyzers, and other diagnostic equipment.
In addition to trucks and buses, diesel mechanics also service and repair construction equipment such as cranes, bulldozers, earth moving equipment, and road construction equipment. The variations in transmissions, gear systems, electronics, and other engine components of diesel engines may require additional training.
To maintain and increase their skills and to keep up with new technology, diesel mechanics must regularly read service and repair manuals, industry bulletins, and other publications. They must also be willing to take part in training programs given by manufacturers or at vocational schools. Those who have certification must periodically retake exams to keep their credentials. Frequent changes in technology demand that mechanics keep up to date with the latest training.