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28 Sep, 2016

Chain-Gang Tech

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Our brutally basic tech articles continue this month with the often overlooked yet critical component of your bike, the chain. When you consider that everything you do while pedalling your bike is transmitted by your chain to your rear wheel, it’s a good idea to learn how to take care of it as well as how to repair a chain when you need to. – BY THE GENTLEMAN RACER
 
A bicycle chain, regardless of speeds or application, is a construct made up out of many different parts to form a whole. Steel plates (cheek plates) are usually stamped out of sheets, then linked together via steel rollers and joining pins. There is a massive amount of effort that goes into designing and building a modern chain. The one constant is the material of choice, stainless steel, which is hard-wearing and has great tensile strength, making it a brilliant material for a bike chain. There are a few exotic chains out there, using titanium and metal-matrix composites, but the vast majority are made of this material.
 
How these chains are designed and manufactured is crucial, as they need to integrate with your cassette and chainrings to provide smooth, secure shifting under severe riding conditions. How severe? Just think of your car’s internal bits working while being on the outside! Manufacturers therefore devote huge resources to getting a chain as close to perfect as possible. For example, when SRAM engineers were asked what part of their new 12-speed Eagle groupsets they were the most proud of, their answer was, “The chain. Definitely the chain.”
 
NATURAL WEAR AND TEAR
Unfortunately, regardless of how well you maintain your chain, it will wear out. This is the “stretch” that people talk about. A chain doesn’t actually physically stretch, but the rollers that link the cheek plates together do wear down, reducing their outside diameter and therefore showing ‘stretch’ when a chain-checking tool is inserted. As these wear down, they also have an effect on the shape of the teeth of your cassette and chainrings.
 
Therefore, it is prudent to replace a chain before it gets a chance to do too much damage to the rest of the drivetrain, but when to replace is a bit of a grey area. Generally, if a chain is replaced at the right time, one can get about two to three chains out of a cassette before it too needs to be replaced, and the same can usually be said for front chainrings. It’s a grey area because wear rates vary, with riding conditions, riding style, and maintenance all coming into play. I always recommend that when in doubt, take your bike to a shop and ask them to measure the chain and inform you of the ramifications.
 
While at your bike shop, ask them to recommend good cleaning and lubing products as well as the correct way to degrease, clean and lube your chain. A practical, hands-on demonstration of the correct procedure is always better than a description of what to do.
 
HERE’S THE FIX
But what do you do when your chain has left you in the lurch and there’s no bike shop in sight? You bought a mutitool with a built-in chain breaker, but how does one actually use the thing? And what went wrong in the first place? Most chain failure is due to a link prizing itself apart as the flanged outer edges of a joining pin fail, and most commonly it is the joining pin that was used to join the chain together in the first place. This is usually due to incorrect installation, but can also just be a tired, stretched chain that’s cried enough while cross-chained and under massive load.
 
I therefore like to keep a SRAM or KMC “quicklink” in my spares box – note that Shimano and Campagnolo don’t produce or advocate the use – making sure I have the correct one for my chain, but to install one you first have to remove the offending link.
 
One needs two ‘male’ (narrower) ends in order to install a quicklink, so the complete damaged link needs to be removed (pic 1). Line up the link to be removed in the chainbreaker so that the joining pin can be driven out by the tool as it is screwed through (pic 2). Joining pins are quite tough to drive through – there is often a loud ‘snap’ as the pin’s flange collapses as it is driven. Drive the pin all the way out of the link (pic 3), leaving your two male ends ready for a quicklink. Slide one half of the link into one chain end and the other half into the opposing side (pic 4). Join the two halves together via their registers (pic 5) and then snap it closed by rotating the chain up toward the top of the chainstay (final pic), holding the rear brake tight while pedalling forward. The chain tension thus created will snap it into place and voila, you’re back in business!