Why Are Our Go Kart Drive Belts Failing?

When your kart's drive belt fails it is quite common to blame the belt quality, but that's not always the case.

The belt failing may simple be the symptom to your problem, the cause of the problem could be much deeper.

In this article we look at some of the primary reasons drive belts fail. The way the drive belt fails usually leaves clues to the cause of the failure.

Match your failed belt to the pictures below and it will give you an indication to the real cause of the failure.

It is quite a technical read (i fell asleep writing it, twice!) but this document has helped several of our customers diagnose and solve their issues of drive belt failure. There is a glossary at the end for all the tech speak.

Cause of Failure - Over Tensioning the Belt

1. Over tension on small pulley's will usually result in land cracks with eventual tooth shear or tensile member break.

2. Over tension on moderate size pulley's will usually result in pulley footprint cracks (root radius cracks) leading to tooth shear and/or tensile member break.

3. Over tension on large pulley's will usually result in the land fabric being crushed under each cord with the cord eventually showing through. The belt will most likely fail by tooth shear or tensile member break.

The corrective action for these types of failures is to reduce the tension of the drive belt. If this is not possible then we would suggest using one of our High Power (HP) belts.

Cause of Failure - Moderate Under Tension

1. Moderate under tension on heavily loaded drives using small pulley's can result in excessive tooth rotation leading to land separation and rubber tear within the tooth body along the cord line. The belt teeth will usually come off in strips and will resemble an adhesion failure.

The corrective action is to increase the belts tension

2. Moderate under tension on moderately loaded drives will usually result in excessive tooth flank wear leading to tooth shear and potential tensile member break. The break will resemble a crimp type failure but the tips or the cord will be frayed.

The corrective action is to increase the belts tension

3. Moderate under tension on lightly loaded drives may result in excessive jacket wear and eventually hook wear on the tooth flank. Shifting the manufacturing length tolerance toward the long side may mitigate or exaggerate this condition. If the belt is on the long side of the length tolerance no abnormal wear may occur. If the belt is to the short side of the length tolerance rapid flank wear may occur.

The corrective action is to increase the belts tension. A special belt length tolerance may in some cases be developed or a modified pulley diameter specified. Cause of Failure - Low Tension

1. Low tension on moderate or heavily loaded drives will result in excessive tooth rotation leading to land separation and rubber tear within the tooth body along the cord line. The belt teeth will usually come off in strips and will resemble an adhesion failure (it is in fact a form of adhesion failure). If the tension is low enough or the load high enough, the belt will ratchet before the land separation/rubber tear occurs. The belt may now fail with a crimp type tensile member break, shock load type tensile member break, belt edge roll up, tooth shear, or the belt jumping off the pulley.

The corrective action is to increase the belts tension.

2. Low tension on lightly loaded drives, if not adjusted for, will usually result in excessive tooth or hook wear. This condition usually occurs where a deep tooth belt is used to compensate for a weak drive structure. The deep tooth is used to prevent belt ratcheting at startup when the structure flexes and the center distance is reduced.

The corrective action is to increase the belts tension. If it is not practical to increase the tension, reduce the belt length or adjust the pulley sizes (diameter) to fit the belt tension required.

Cause of Failure - Pulley Misalignment

1. Angular shaft misalignment or tapered pulleys, belts run on drives with angular shaft misalignment's or tapered pulleys will exhibit a tapered wear pattern across the belts tooth flanks as well as tapered compaction in the lands. Belt failure will normally occur by tooth root tears starting on the side of the belt that is carrying the most tension on the pulleys and then propagating across the belt width resulting in tooth shear. The edge of the belt may also show significant wear due to the high tracking force and may even roll up or try to climb over the pulley flange.

The corrective action - align drive or replace tapered pulleys.

2. Parallel Misalignment belts running on drives that have parallel misalignment will usually show excessive belt edge ware on both edges of the belt. Belt failure will normally occur by tooth root tears starting from both edges of the belt eventually extending across the width of the belt resulting in tooth shear.

The corrective action - align drive or replace tapered pulleys.

Cause of Failure - Extreme Pulley Run-out

The lands of belts run on drives with extreme pulley run-out will have a crushed appearance similar to belts run at high tension on moderate sized pulleys. The belt will usually fail by tooth shear or tensile break. This type of failure most often occurs where bushed pulley's are used and the recommended bushing installation procedure was not followed or where a minimum plain bore pulley was improperly bored.

The corrective action is to reinstall and realign the bushed sprockets or, replace the plain bore sprockets.

Cause of Failure - Sustained Belt Overload or Too Few Teeth in Mesh

1. Wire belts, mold side of twin power belts, belts with shimmed or heavy upcoated jackets will fail when the rubber between the cord and the jacket tears (land separation) or in the case of the wire belt when the jacket separates from the wire in the land area. the belt teeth will come off in ribbons rather than by individual tooth shear. This is because the rubber between the cord and the jacket cushions the land allowing the belt to run until the cushion layer tears.

The corrective action is to reduce the belt load by increasing the pulley sizes or increasing the belt width.

2. Other belt constructions and the press side of twin power belts assuming that the tension is adequate to prevent tooth jump, these belts will fail by root cracks or pulley footprint cracks resulting in individual tooth shear. Many times strips of land fabric will remain adhered to the belt carcass. This is because the rubber between the cord and the jacket cushions the land allowing the belt to run until the cushion layer tears.

The corrective action is to reduce the belt load by increasing the pulley sizes or increasing the belt width.

Cause of Failure - Intermittent Belt Overload or Too Few Teeth in Mesh

1. Wire belts, mold side of twin power belts, belts with shimmed or heavy upcoated jackets will usually show multiple land delaminations around the belt with the final failure being a ribbon of teeth coming off. This type of failure starts with a small crack occurring between the tooth rubber and jacket in the root radius.

The corrective action is to reduce the belt load by increasing the pulley sizes or increasing the belt width.

2. Other belt constructions these belts will sometimes show a higher degree of root radius - upper flank jacket damage on the teeth in contact with the pulley at the time of the overload. Primary failure is usually rupture of the jacket in the root radii resulting in full or partial tooth shear (loose teeth) around the belt with the final failure being a group of sheared or loose teeth. Belt teeth may have a cored appearance. That is the rubber will be missing from the center of the belt leaving the jacket intact.

The corrective action is to reduce the belt load by increasing the pulley sizes or increasing the belt width.

Cause of Failure - Abrasive Atmosphere

Belts run on new pulleys in an abrasive atmosphere such as foundry shakers, taconite processing equipment and phosphate mining conveys will usually exhibit a high degree of land and tooth flank wear (hook wear). The worn areas will frequently have a polished appearance. The pulleys generally show sever wear as well and need to be replaced along with the belt.

The corrective action is to protect the drive from the abrasive atmosphere or continually replace the belts and pulleys as often as needed.

Cause of Failure - Worn Pulleys

Worn pulleys are most commonly found where an abrasive atmosphere is present. They can also occur on drives that are subject to high installation tension or on drives where the belt is allowed to run past it's useful life. When the jacket in the land area wears through the cord will make contact with the pulleys outer diameter (OD). This will result in rapid wear of the pulleys OD. Pulleys used in abrasive atmosphere will exhibit both groove and OD wear. Belts run to failure on sprockets will usually exhibit polished land wear and may or may not have tooth hook wear. NOTE: A good indication of worn pulleys is when a mechanic reports that the first belt on the drive lasted a long time and the life of the replacement belt was considerably less.

The corrective action is to replace the pulleys

Cause of Failure - Pulley Diameters Out of Specification

Pulley Diameters Out of Specification this is probably the most difficult failure to analyse unless the pulleys are grossly outside of diameter tolerance. Belts will usually show a high degree of tooth flank wear with the jacket flank exhibiting a silver/grey fuzzy appearance in the worn area with the land fabric appearing normal. Land separation caused by tooth rotation may or may not be present. Long or short belts may perform better than nominal length belts - especially on fixed center drives. If no other cause for the failure can be determined, question the pulley diameters.

The corrective action is to replace the sprockets.

Cause of Failure - Heat Degradation

Heat degradation, neoprene belts run for a prolonged period of time at elevated temperatures will increase in hardness until the back of the belts crack. The back cracks will always be parallel to the belt teeth and will usually be over the lands. If allowed to continue to run, the belt will eventually fail by tensile member break. These belts are easily identified by the back cracks and the increase in rubber duromenter. When a urethane belt is exposed to elevated temperatures the adhesion of the urethane to the tensile cord will lose its integrity. Furthermore, the teeth may soften and deform, resembling a melted belt.

The corrective action is to use a heat resistant belt construction.

Cause of Failure - Chemical Degradation

Chemical degradation, neoprene belts subjected to either organic solvent vapors or ozone will resemble belts subjected to high temperature in that they will appear to be hardened and will exhibit back cracks. The differences are the the hardening will usually be on the surface of the belt and the back of the belt will be cracked in the longitudinal as well as lateral direction. The back of the belt will often have a crazed or checked appearance.

The corrective action is to obtain as much detail about the application as possible and look for an alternative belt construction.

Cause of Failure - Oil Contamination

Oil contamination, the operation of a neoprene belt in an oily atmosphere will result in swelling of the rubber and loss of adhesion between the rubber and the cord and between the land jacket and the cord. The first indication of imminent belt failure will be the separation of the land fabric from the cord. Ultimate failure usually resembles belt tooth shear.

The corrective action is to use an oil resistant belt construction.

Cause of Failure - Sub-minimum Pulley Diameter.

Sub-minimum pulley diameter, curviliner belts run on sub-minimum pulley diameter will usually fail by land disintegration and tensile break. Trapezoidal belts will usually fail by tooth root cracks and tooth shear although tensile breaks are not uncommon.

The corrective action is to increase the pulley sizes if this is not possible performance can sometimes be improved by using a shallow groove-wide land pulley design and/or a more flexible belt construction.

Cause of Failure - Crimp Failures

Crimp cord failures, are usually associated with mishandling the belt but there are some other causes. Crimp failures can be caused by belt self tensioning, a foreign object in the pulley grove preventing the belt tooth from meshing with the pulley groove or low tension allowing the belt tooth to hit on the land of the pulley and then fall or snap back into the pulley groove (self tensioning). Belts are more susceptible to crimp damage from back bending rather than forward bending.

Cause of Failure - Shockload

Shockloading, is the transient application of loads significantly beyond design load. The belt teeth in contact with the pulley at the time of the shock load will usually show root radius damage with possible tooth shear. The broken tensile member will exhibit a ragged, uneven appearance across the break. The remainder of the belt may appear to be in much better condition. This can occur on a track which has potholes or a track which has bridges or second levels which cause excessive breaking on level changes.

The corrective action is usually to purchase our high powered belts and if the track has excessive potholes then try a more flexible belt construction.

Cause of Failure - Foreign Objects

The introduction of debris between the pulley and the belt effectively increases the belt tension beyond design limits resulting in rupture of the tensile members. This can occur at outdoor tracks when a kart goes into a gravel trap.

The corrective action for this is to regularly sweep your track and remove gravel traps.

Cause of Failure - Normal Wear and Failure

Normal belt wear, will closely resemble a premature belt failure, the only main difference is the period of time that it takes the belt to get to that point. The ideal failure type of a synchronous belt would be a tensile failure. However, the more common type of failure would result in tooth derogation resulting from tension, alignment problems and the pitch fit of the pulleys.

If you have made it this far you deserve a medal!

and if you are still having issues why not call our technical team who can help you sort this out.

Glossary

Land: the gap between the belts teeth.

Jacket: the outer coating of the tooth and land (or the inside fabric of the belt).

Cord Line: most belts have cord fibers running through them they could be fiberglass or Kevlar.

Tooth Root (Root Radii): where the belt tooth meets the belt land.

Jacket Cushions: the rubber of the tooth underneath the jacket.