Chain wear measurement
A chain wear measurement is used to determine the degree of wear of a drive chain in the form of its elongation ; the term is usually used in connection with bicycle chains . A degree of wear recognized in good time can be used to replace the chain in order to protect the sprockets, pinions, sprockets or chainrings that come into contact with the chain.
Chain wear due to elongation
Drive chains wear out due to the wear and tear of the link connections between the pin, bearing collar or sleeve and roller, which work as a sliding bearing, when the chain rolls over the sprockets, chainrings and pinions of the sprockets and the links are deflected. In a well-maintained chain, this wear occurs largely evenly on all links.
If the chain is very elongated, the distance between the chain links (the “pitch”) no longer correctly matches the distance between the teeth on the sprockets. The power transmission is then only concentrated on a few contact points in front of the pulling chain strand , the chain also migrates relatively outward from the "valleys" of the teeth and "digs" into the load-side flanks of the sprocket teeth, which makes them considerably faster than with wear out on a new chain. An elongated chain no longer runs quietly and cleanly. For chain drives with low basic tension, e.g. B. in derailleur gears with a spring-loaded chain tensioner in the rear derailleur , under heavy loads this can even lead to the chain climbing out of the teeth and slipping through and several teeth jumping further.
To prevent this, the chain should be replaced with a new one when it reaches a defined level of wear. Alternatively, it is possible to drive the chain and the entire drive train as long as possible and then change chainrings and sprockets together with the chain. It is controversial among frequent travelers which approach is cheaper in the long term.
The chain wear can be determined with a chain gauge or a caliper .
There are monitoring systems for chains in the industrial sector that provide information about the chain elongation during operation.
Measurement methods for bicycle chains
There are several measurement methods with different measurement tools that can be used on bicycle chains. It is important for all measuring methods to subject the chain section to be measured to a certain pretension in order to displace the lubricant (chain grease) present in the links and to eliminate this possible cause of incorrect measurements.
Review with a lesson
A chain gauge is placed on the assembled chain that is tensioned by force on a pedal. If this is worn out, the gauge dips more or less deeply into the chain. This control is very quick and replaces the subjectively influenced pulling of the chain from the largest chainring, which was the common method until this type of tool was introduced. Such gauges are suitable for all common circuit chains, including 9 and 10-fold wreaths.
Please note that there are two different types of chain gauges: those that move the rollers in opposite directions when inserted (like the one shown) and those that move the rollers in the same direction. The first variant is only reliable if the rollers are made of extra hardened material and therefore hardly wear out, because their wear is included twice in the measurement with this teaching. This means that for most chains it is indicated far too early that the wear limit has been reached. The more precise results are provided by teachings based on the second principle mentioned, since the wear of the rollers (which has no influence on the chain elongation and is therefore irrelevant) does not falsify the result.
Since sprockets and chainrings made of steel are less sensitive to wear from elongated chains than those made of aluminum, a slightly higher wear of the chain is acceptable with the former before it attacks the sprocket. Many chain gauges therefore have two sides; one for aluminum (wear dimension 0.075 mm per joint) and one for steel (wear dimension 0.1 mm per joint).
Measurement with a vernier caliper - internal measurement variant
A standard caliper is first set to a length of approx. 118 mm and, as shown in the picture, inserted between ten chain links at any point on the chain. Now the caliper is opened further until it rests on the rollers of the chain links. The length now measured is 119.5 mm for a new chain. From 120.25 mm for aluminum sprockets / chainrings or 120.5 mm for steel sprockets / chainrings, the chain is so long that it should be replaced. It must be ensured that the sharp edges of the inside measuring legs of the caliper lie cleanly on the circumferential surfaces of the rollers and do not slide into the gap between the roller and the bracket, which would lead to an incorrect measurement.
Measurement with a vernier caliper or ruler - external measurement variant
The length of ten tensioned chain links (five inside, five outside) is determined using the caliper or a ruler based on the position of the rivets or a comparable, defined point, e.g. B. always measured the left or right edge of an outer flap. In each case, the same point of the rivet or tab is to be assumed, so z. B. each left or the middle of a rivet.
The measured values mean:
- 127 mm: good,
- 128 mm: change,
- 129 mm: the teeth of the chainrings and sprockets are already wearing out
- 130 mm: worn teeth can be assumed.
This variant is recommended occasionally, as the inside distance measurement or the gauge can indicate wear too early, depending on the type of chain.
Wear mark on motorized two-wheelers
In many motorcycles and small and light motorcycles , the chain tension is adjusted by moving the rear axle in elongated holes in the swing arm or by using an eccentric mechanism in one-sided swing arms. Markings are often attached here, which, in addition to correct centering of the rear wheel when the chain is being tensioned, also use a colored marking to indicate that, based on the position of the center distances achieved, the chain is so long that it should be replaced - if necessary together with the complete set of sprockets. However, these indicators only relate to linear elongation-related wear, other types of damage such as B. stiff, stiff chain links due to insufficient lubrication or corrosion due to defective O-rings cannot be easily identified using these markings.
Continuous wear measurement
For industrial machines and systems, the German chain manufacturer Iwis has been offering a wear measurement system called CCM ( chain condition monitoring ) since the beginning of 2016 . The device uses sensors to continuously measure the wear elongation of chains during use. It thus helps the maintenance staff to recognize in good time when a chain needs to be retensioned or replaced due to wear elongation. Monitoring takes place during operation; the machine in question does not have to be stopped for this.
literature
- Rob van der Plas: The bicycle workshop - repair and maintenance step by step. 1st edition, BVA Bielefelder Verlaganstalt, Bielefeld, 1995, ISBN 3-87073-147-8 .
- Michael Gressmann, Franz Beck, Rüdiger Bellersheim: specialist knowledge of bicycle technology. 1st edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 2006, ISBN 978-3-8085-2291-2 .
- Richard Hallet: Bicycle Maintenance-Care-Repair. 1st edition, BVA Bielefelder Verlag GmbH & Co. KG, Bielefeld, 2003, ISBN 3-87073-308-X .
Web links
Individual evidence
- ↑ Tensioning the chain properly - Tension is what counts Article on motorrad-online, accessed on May 2, 2018
- ↑ Chain elongation monitoring system CCM website iwis drive systems