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Check Belts And Chains For Wear

Newer engines often have spring-loaded tensioning mechanisms on accessory drives, but don’t skip an inspection of these belts because of that

When it comes to running engine accessories, such as alternators and water pumps, tension specs for V-belts are generally supplied by the machine manufacturer. If you don’t have the necessary specs for an engine’s belts, they should generally deflect one inch (25 mm) with a force of 25 lbs. (110 N) applied midway between pulleys. This can be accurately checked with a straight edge and a ruler, if you don‘t have the special tool for doing it.

Newer engines often have spring-loaded tensioning mechanisms on accessory drives, but don’t skip an inspection of these belts because of that. Springloaded tensioners can seize up from running in one position for extended periods. This causes them to lose their ability to apply spring load on a belt; be sure to check them, too.

Drive belts start to fail when cracks on their underside become too dense, too deep or both. Glazing of a belt’s sides occurs when it has run for long periods while slipping. The excess heat generated by a slipping belt will eventually lead to total failure. This kind of wear eventually causes a belt’s cross-section to develop an hour-glass appearance. It is typical of a pulley spinning with the belt not moving due to an overload.


Chains need periodic tension maintenance, too. And just like belts, they can eventually stretch.

Chain manufacturers use a numbering system to denote size. The most common sizes on farm machines range from #40 to #80. The numbers represent the pitch of the chain, which is the pin-to-pin dimension of each link. To find the actual measurement, take the first digit and multiply by 1/8 of an inch. For example, a #50 chain will have a pitch dimension of 5 X 1/8 of an inch, which equals 5/8 of an inch, or 0.625 inches (5 8 = 0.625 inches).

As a chain wears over its lifetime, the gaps between the pins and bushings increase. This causes the effective pitch to increase. Once the pitch increases by three per cent, it is time to replace the chain. For example, a 50-inch chain can increase in length by 1.5 inches before it is necessary to replace it (0.03 x 50 inches = 1.5 inches). Continued use of a stretched chain will start to wear the sprockets it runs on due to the climbing effect caused by the increased pitch.

No one likes to be bogged down by a breakdown in the busy season. Proper maintenance and checks of belts and chains in a detailed, preseason inspection could save a breakdown from happening. Aside from improving machine performance, it can save you money and reduce downtime in the field.

Dietrich Schellenberg, Marty Zuzens, Peter Lung and Dennis White are instructors at Assiniboine College’s School of Trades and Technology at Brandon, Man (

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