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Transmission and failure of camshaft

Update:23-11-2021
Summary:

Camshaft transmission Common transmission modes between […]

Camshaft transmission
Common transmission modes between camshaft and crankshaft include gear transmission, chain transmission and toothed belt transmission. The transmission between the lower camshaft and the middle camshaft and the crankshaft is mostly driven by cylindrical timing gears. Generally, only a pair of gears is required from the crankshaft to the camshaft. If the diameter of the transmission gear is too large, an additional intermediate can be added Idler. In order to mesh smoothly and reduce working noise, most timing gears use helical gears.
Chain transmission is common between overhead camshaft and crankshaft, but its working reliability and durability are not as good as gear transmission. Toothed belts are widely used instead of transmission chains on high-speed engines, but chain transmission is still used on some high-power engines. Toothed tape has the characteristics of low working noise, reliable working and low cost. For dual overhead camshafts, generally the exhaust camshaft is driven by the crankshaft through a timing belt or chain, and the intake camshaft is driven by the exhaust camshaft through a metal chain, or both the intake camshaft and the exhaust camshaft are driven by the crankshaft. Driven by the crankshaft through toothed tape or chain.

Camshaft failure
Common failures of camshafts include abnormal wear, abnormal noise, and breakage. Symptoms of abnormal wear often appear before abnormal noise and breakage occur.
(1) The camshaft is almost at the end of the engine's lubrication system, so the lubrication status is not optimistic. If the oil pump has insufficient oil supply pressure due to reasons such as excessive use time, or the lubricating oil passage is blocked and the lubricating oil cannot reach the camshaft, or the tightening torque of the bearing cap fastening bolts is too large, the lubricating oil cannot enter the camshaft gap. Cause abnormal wear of the camshaft.
(2) Abnormal wear of the camshaft will cause the gap between the camshaft and the bearing seat to increase, and the camshaft will undergo axial displacement when it moves, which will cause abnormal noise. Abnormal wear will also cause the gap between the drive cam and the hydraulic tappet to increase. When the cam is combined with the hydraulic tappet, an impact will occur, which will cause abnormal noise.
(3) The camshaft sometimes has serious failures such as fractures. The common reasons are hydraulic tappet cracking or severe wear, severe poor lubrication, poor camshaft quality, and camshaft timing gear rupture.
(4) In some cases, the failure of the camshaft is caused by man-made reasons, especially when the camshaft is not properly disassembled and assembled when the engine is repaired. For example, when removing the camshaft bearing cover, use a hammer or a screwdriver to pry pressure, or when installing the bearing cover, the wrong position causes the bearing cover and the bearing seat to not match, or the tightening torque of the bearing cover fastening bolt is too large. When installing the bearing cover, pay attention to the direction arrow and position number on the surface of the bearing cover, and use a torque wrench to tighten the bearing cover fastening bolts in strict accordance with the specified torque.

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