Engine belts rose to popularity in the 1970's,and are one of the most inexpensive, efficient ways to transfer power between shafts, that may not be axially aligned. Belts are looped over pulleys, which they transfer their power to the shaft, that they are attached to. Belts run with little noise and are very smooth. They also help to cushion the motor and bearings against load changes that the shafts are producing. These belts obtain their strength by reinforcements with fibers like steel, polyester or aramid. The usual failure signs of a belt include either stripped teeth which will leave a smooth section of belt where the drive cog will slip or delamination and unraveling of the fiber cores. Belts will degrade faster when exposed to things such as mud, water, motor oil, and other fluids which is why leaky and dirty engines will need the belts changed more often.
V belts were developed in 1917 and helped solve the slippage and alignment problem that plagued belts from being successful before that. V belts provide the best combination of traction, load of the bearings, long service life, and speed of movement. This belt has a trapezoidal cross-section of a “V” shape in the belt which tracks in a matting groove in the pulley which helps keep the belt from slipping off. This belt also tends to wedge itself into the groove more as the load increases which improves torque transmission and making the V-belt an effective solution to the flat belt.
The optimal speed range for a V belt is around 1000-7000 ft/min. V belts are wider than the normal flat belts which give them more traction on the pulleys, but also help them to last longer. For applications with a high power requirement, V belts can be aligned side by side in an arrangement called muti-V which runs on matching muti-groove pulleys. There are also jointed and link V belts which use rubberized fabric links held together by metal fasteners. These belts however are only able to run at speeds up to 4000 ft/min. The advantage is that they are length adjustable by removing links when needed.
Serpentine belts were first introduced in 1985 and used to drive multiple peripheral devices in an automobile engine. Things that it may drive can include the water pump, compressor, air pump and alternator. This belt may also be guided by an idler pulley or a belt tentioner. This belt is more efficient than the older multiple belt systems and consumes less space in the engine compartment. By using one thick belt instead of multiple skinnier belts, you are able to put the belt under more tension without stretching it. With higher tension comes less slip, therefore increasing mechanical efficiency and the belt life. This belt also eliminated the problem when using multiple V belts where they would flip over in the pulleys groove at high RPM’s. Serpentine belts are also easier to replace and maintain since there is no need to replace and remove multiple belts when doing so. With only one movable belt tentioner, all the peripheral components can just be mounted to the engine without the need to swivel.
Timing belts are positive transfer belts that can track relative movement. This belt is part of the engine and controls the timing of the engines valves. Timing belts replaced the timing chains that were popular until the early 1970’s. This belt has teeth that fit into a matching toothed pulley. When this belt is correctly tensioned, they run at a constant speed, have no slippage, and will transfer direct motion for indexing or timing purposes. Advantages of a belt over chains or gears include not having to lubricate it, and less noise being created. Timing belts need the least tension out of all the belts and are among the most efficient. These belts can handle up to 200 hp at speeds of 16,000 ft/min.
Timing belts can also come with a helical offset tooth design. The helical offset tooth design creates a chevron pattern which allows teeth to engage progressively. This pattern is self aligning and is more efficient at transferring power. Newer timing belts also incorporate curved teeth instead of the old trapezoid shaped teeth which helps them last longer, and is quitter. When replacing a timing belt, care must be taken to ensure that the valve and piston movements are correctly synchronized. If not synchronized properly when replacing the timing belt, you can experience problems with valve timing, which can cause a collision between valves and pistons. To help protect against this, timing belts have painted marks on them to help ensure that you align them properly on the camshaft gears and crankshaft gear. Timing belts are usually covered by metal or polymer timing belt covers which help keep them from being exposed to the elements. Timing belts are typically replaced every 60,000 to 90,000 miles to avoid a breakdown; if the belt breaks the engine will not be able to run.
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