Have a couple of belts

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Funny how the most uncomplicated vehicle components can give you a bad day – when they fail.

Take, for example, the lowly v-belt. It’s been driving accessory devices like water pumps and alternators (originally, generators) for more than a century. Of course, serpentine setups with automatic tensioners have become the rule on today’s trucks.

“Most everything we see now is being built with serpentines,” says Dave Foster, vice president of field maintenance for Southeastern Freight Lines, based in Columbia, S.C.

Still, there are plenty of v-belts out there. And they still can fail, and leave a vehicle immobilized.

“I think the biggest problem with v-belts is getting the tension correct on them from the start,” adds Foster. That makes sense, and I’ve seen loose belts fray as they flop up and down in their pulleys. Plus, belts that are too tight can put extra wear on pulley bearings.

Speaking of pulleys, there are other conditions that can cause problems. According to a proposed Recommended Practice (RP) from the Technology & Maintenance Council (TMC), 346A, “Accessory belt drive pulley standardization,” there are a couple of ways
pulley mismatch and/or misalignment can adversely affect v-belt life.

One, says the proposed RP, is groove size mismatch (see Figure 1). This can occur when a component is replaced and has its own pulley that doesn’t match up with the driving pulley. The result is excessive belt flexing and fatiguing.

Another potential problem is pulley groove spacing mismatch (see Figure 2). This can have the same cause and effects as pulley groove size mismatch, but also can be caused by manufacturing variances among suppliers.

How to avoid these perils? The proposed RP suggests:

  • Defining dimensional data and methods of measurement for belts and pulley components;
  • Defining a unified practice to obtain commonality within the marketplace;
  • Providing a benchmark on which to conduct quality audits; and
  • Defining limits for approval.

Standards for belts and pulleys have been defined and are available from the Society of Automotive Engineers (www.sae.org). Also, belt manufacturers usually can provide templates to check for compliance with established standards.

With this information, er, under your belt, you may be able to prevent a costly breakdown.