Wednesday, 10 August 2011

Bike chains: how to inspect, replace, fit, clean and lubricate

Figure 1. The Shimano Length Check (see 2(a) below).

Fitting a new chain should be easy and satisfying. Yet, it's possible to make a miserable, muddlesome meal out of it. I know, I've been there! Generally, the objective is to ensure that the chain is as short as possible and suits the gearing system on the bike. So, after all my trials and tribulations on the subject, here's how I've learned to go about it:

Derailleur equipped bikes

1. Assess the chain's condition. Is it enough to merely clean it up, or should it be replaced? Is there a special joining link? What kind of chain is it? Buckled links, damaged plates, or severe rust point to changing it. I measure the wear, or "stretch" as its sometimes called, using a steel foot ruler. I put the zero mark on the centre of a rivet pin. Measure 12" and if the chain is not worn, there should be the centre of a rivet pin at the 12 inch mark exactly. I put a bit of pressure on the pedal with my free hand while I do this, to ensure that slack in the chain is taken up. If the centre of the pin is more than ~1mm past the 12" mark, then I replace the chain. If it's greater than ~1.5mm past the 12" mark, then I'd replace the cassette too. Otherwise, the chain may slip on the old worn cassette. It can get expensive if the chainring teeth are worn as a result of a knackered chain, so it's wise to assess chain stretch regularly.

2. Is the current chain the correct length? On a bike I'm not familiar with, I do all three of the following length checks:

(a) The Shimano length check. With bike on level ground, shift the chain on to the biggest chainwheel and smallest rear sprocket. The axes of the jockey wheels on the rear derailleur should line up vertically (or close to vertical), one above the other, with the line perpendicular to the ground. See Figure 1 above.
Figure 2. Tautest Setting Check.

(b) Tautest setting check. Change shift levers so that the chain is in its most taut setting, that is on the biggest chainwheel and also the biggest sprocket. If the chain is too short, this setting cannot be achieved without something breaking! Although the big-big combo should not be used in practice, I think it's very important that it can be engaged, or damage could occur when shifting into that setting accidentally. The rear derailleur will be angled forward and the chain should show at least a slight S bend as it goes around the jockey wheels. The chain should not be too stretched out through the wheels. See Figure 2 above.

(c) Slackest setting check.
Change shift levers to put the chain on the smallest front ring and smallest back sprocket. The rear derailleur should be coiled up, the chain should Z bend round the jockey wheels. There should be minimal slackness in the bottom run of the chain and no interference between jockey wheels, derailleur arms and the free runs of the chain. Again, the small-small combo should not be used, but it needs to work without fouling or excessive chain slackness. (Figure 3)
Figure 3. Slackest Setting Check.

Ideally, the chain should pass all three length checks, but the Tautest and Slackest ((b) and (c) above) are the most important ones! Doing them all gives me a clear idea as to whether the current chain is the right length, too long or too short.

3. Decide which chain to buy. This means thinking about its size, type, brand, quality and joining method. If I know the bike is going to be muddy and wet frequently then I would go for one with corrosion resistance - e.g stainless steel, or at least nickel or brass coated. I choose the speed and the brand, the big boys are Campagnolo, KMC, Shimano, SRAM and Wippermann, and then there are a whole host of smaller suppliers. I've tried all of the big brands and have found something to like in each of them. How do I choose the type? Well, past experience is a good guide, as are the views of others, although I don't always agree with them! Generally, I find that very cheap chains tend to be poor quality, deform easily and wear out quickly. Price is a big factor. Another is the joining method - personally I like SRAM powerlink/powerlock connectors (you pinch them), but they are not the only option for quick links. Joining with rivets is not a problem, but is less convenient for taking the chain occasionally for cleaning or access.

4. Remove the old chain. In step 1 above, I checked whether there was a joining link, right? If there's no quick link joining mechanism, I'd resort to a chain tool. It needs to be a suitable size (and speed) for the chain - it's basically a rivet extractor that uses a screw mechanism. Clean up the derailleurs, chainwheel teeth, cassette and any other bits that need sprucing up. I lube the derailleurs at this point because access is easy.

5. Cut the new chain to the right length. Measure, measure and measure again before cutting! If the original passed all three length checks, then count its links (do it a few times to check!) and cut the new chain to the same length. Otherwise, I use the Shimano length check (see 2(a) above) and/or the following easy one:

(a) SRAM length check. Put the chain on the biggest chainwheel and biggest sprocket. Do not run it through the rear derailleur. Take up all the slack and bring the ends together tight. From where the ends would join up, add a further 2 links and the powerlink. This usually works, but it may depend on the on the derailleur design, so be careful - I use the SRAM length check and/or the Shimano length check just to establish an initial guestimate (see Figures 1 and 4).

Figure 4. SRAM Length Check.

6. Join ends and do the three length checks. This is where a quick link is great, because I can connect the chain, test it using the Tautest setting and Slackest setting length checks above, and if necessary change its length, taking apart and re-joining easily. Note that 10 speed SRAM powerlock connectors are one time only, whereas 9 and lower speed powerlink ones can be re-used. When joining Shimano chains use their special joining rivet and remember to check the manual to ensure it goes in the correct orientation in the link. Whatever the manufacturer, read their instructions for connecting and adhere to them.

7. Lubrication and cleaning. I leave the manufacturer's lubricant on the chain for as long as I dare. Keep the chain clean and lube it only when it's clean and dry - because dirt can act as a grinding paste in the oil. If you clean with soapy water, then make sure you wash it off thoroughly with clean water, because many soaps (e.g. washing up liquid) contain salt, which stimulates corrosion! Degreaser, paraffin, white spirits are all possible cleaners depending on the state of the chain. I use one of "the boss's" discarded baking trays as a washing pan for the chain. Let it dry off well.

Chain cleaning and lubrication is a subject that can generate much discussion and spark heat among cyclists! There are many different schools of thought on it. I find that astonishing for an invention that's well over a century old! Personally, I oil each link joint on the inside of the chain (that's the side closest to the chainwheel teeth) along the bottom run of the chain. That way it does not go all over the place, only to where it's needed. Then rotate the pedals backwards a number of times to work the oil in. Wipe off excess oil along the chain using a clean cloth - I put my hand in an old soft sock and hold the chain while pedalling backwards. I agree with the experienced time triallists who tell me that a clean, oiled and unworn chain is worth many seconds in the race of truth!

Single speed or hub gear bikes

The general objective and thought process is very similar to that described above, but since there is no sprung derailleur and only one sprocket and chainwheel, setting chain tension can be tricky. So note the following additional point:

8. Look for tension adjustment. When assessing the chain's condition - along the lines described at 1. above - I would also inspect the bike for methods of chain tension adjustment. For example, by sliding the wheel axle back and forth in the rear dropouts, an eccentric bottom bracket system, a chain tensioner or even a jogged link (half link). Indeed, it may be worth considering a half link chain (that's one made entirely of jogged links). This could be handy where there is little other provision for chain tension adjustment. They also look dead cool!

There's something therapeutic about a new, or freshly cleaned, chain. It feels cathartic to ride off on the bike afterwards - not to mention a little nippier!


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