ENGINEMAN 1 & CA different type of drive gear mechanism isused for a four-stroke cycle, V-type gasolineengine. The camshaft gears are driven through atrain of bevel gears from the crankshaft. This ar-rangement serves to drive not only the camshaftbut also other accessories, such as a magneto, ordistributor, a fuel pump, and a tachometer. Anadditional gear, called the oil and freshwaterpump drive gear, meshes with the crankshaft gear.The causes of gear failure (improper lubrica-tion, corrosion, misalignment of parts, torsionalvibration, excessive backlash, wiped gear bearingsand bushing, metal obstructions, and impropermanufacturing procedures) are basically the sameas the causes of similar troubles in other engineparts. The best method of prevention is to adhereto the prescribed maintenance procedures andfollow the instructions given in the manufacturer’stechnical manual.Maintenance and repair of gear trains involvea thorough check (for scoring, wearing, pitting,etc.) of the gear shafts, bushings and bearings,and gear teeth during each periodic inspection.Be sure that the oil passages are clear, and thatthe woodruff keys, dowel pins, and other lock-ing devices are secured to a tight fit in order toprevent longitudinal gear movement. It is essen-tial that all broken or chipped parts be removedfrom the lubrication system before new gears areinstalled.An engine must not be barred over while thecamshaft actuating gears are removed from thetrain. Should the engine be barred over, there is75.239Figure 3-25.—Checking clearance of positive displacement blower lobes.3-38
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