page_title: Toothed belt
section_title: Belt failure
hierarchical_section_title: Toothed belt / Belt failure
caption_attribution_description: English: 2001 Honda Accord timing belt. Don't do this with timing belts, the tight flexure of knotting them damages the internal reinforcement)
context_page_description: A toothed belt; timing belt; cogged belt; cog belt; or synchronous belt is a flexible belt with teeth moulded onto its inner surface. It is designed to run over matching toothed pulleys or sprockets. Toothed belts are used in a wide array of in mechanical devices, where high-power transmission is desired.
context_section_description: Toothed belts have two failure modes, one gradual and one catastrophic. There is an increased risk of either over the lifetime of the belt, so it is common for highly-stressed belts to be given a service lifetime and to be replaced before this failure can occur.
  One failure mode is gradual wear to the tooth shape, which may eventually lead to slippage over rounded teeth. The belt often continues to work, but the relative timing between shafts changes.
  The catastrophic failure mode is caused by delamination between the belt and its fabric reinforcement. Although this may be caused by age and wear, it is often accelerated by mistreatment of the belt, often during initial installation. Overloading the belt by bending it to a narrow radius is a common cause of damage, either by bending out of the belt's designed axis, twisting, levering it into place with tools, bending in the correct axis but to too small a radius, or even knotting a belt in storage. Another cause, particularly with natural rubber belts, is contamination by oil, especially to the edges where the reinforcing fabric is exposed and can cause a wick effect.
  It is extremely rare for a timing belt to break. More common is for the belt to delaminate, disconnecting the fabric strength member from the teeth that ride on the pulleys. The belt is then often thrown from the pulleys and may be further damaged, cut, or break. Although worn teeth may be detectable by careful inspection, internal deterioration is not considered to be reliably detectable and so the observance of service lifetimes is important.
caption: A new belt, already damaged by knotting
exif: {"Image Make": "Canon", "Image Model": "Canon EOS 40D", "Image Orientation": "Horizontal (normal)", "Image XResolution": "240", "Image YResolution": "240", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS4 Windows", "Image DateTime": "2010:10:21 20:48:12", "Image Artist": "Oto Godfrey", "Image YCbCrPositioning": "Co-sited", "Image Copyright": "Creative Commons Attribution-Share Alike 3.0 Unported", "Image ExifOffset": "308", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "906", "Thumbnail JPEGInterchangeFormatLength": "3924", "EXIF ExposureTime": "4", "EXIF FNumber": "13", "EXIF ExposureProgram": "Aperture Priority", "EXIF ISOSpeedRatings": "160", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2009:11:30 01:13:44", "EXIF DateTimeDigitized": "2009:11:30 01:13:44", "EXIF ComponentsConfiguration": "YCbCr", "EXIF ShutterSpeedValue": "-2", "EXIF ApertureValue": "7400879/1000000", "EXIF ExposureBiasValue": "-2", "EXIF MaxApertureValue": "19/4", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash fired, compulsory flash mode", "EXIF FocalLength": "44", "EXIF SubSecTimeOriginal": "00", "EXIF SubSecTimeDigitized": "00", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "3888", "EXIF ExifImageLength": "2592", "Interoperability InteroperabilityIndex": "\u0001\u0001\u0001\u0001", "Interoperability InteroperabilityVersion": "[3, 0, 0, 0]", "EXIF InteroperabilityOffset": "776", "EXIF FocalPlaneXResolution": "324000/73", "EXIF FocalPlaneYResolution": "2592000/583", "EXIF FocalPlaneResolutionUnit": "2", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF SceneCaptureType": "Standard"}