Introduction

This article is for everyday cyclists.

 

WHAT YOU NEED TO KNOW

PRECONDITIONS: You will need a chain rivet extractor, and possibly a chain wear indicator, for this fix.

TIME: 1 hour

WARNING: If your old chain has worn down your cassette and chainring, you will need to replace all three components - a much longer job.

DIFFICULTY: Intermediate. A dirty job, which needs some thought and quite strong wrists.

STEPS

1. Measure the chain wear

2. Do you need to replace a) your chain, or b) your chain, cassette and chainring?

3. Remove the chain

4. Thread the new chain

5. Check chain length and shorten

6. Join ends together

7. Check chain moves freely

 



1. Measure the chain wear

Replace a chain that has stretched: You need to replace a chain, if you have cycled so far that the chain has stretched beyond acceptable limits. A bike chain inevitably stretches with use, so you need to replace it before the now-too-long links wear down the teeth on your cassette and chainring, and you need to replace all three components.

Measure chain stretch: It is impossible to judge chain stretch with the naked eye - it just feels 'loose' or 'chewy' when you pedal. It is also impossible to say for how many miles a chain will last - it depends how clean you keep it, and how durable the chain. So use a Chain Wear Indicator to measure the length of your chain links.

Place one end of the longer side of indicator into the chain. This longer side might be marked '1%' wear, for example.

If the other end of the indicator drops into the chain, then the chain needs replacing now. The chain has stretched too much.

 
replace chain now
Longer side of indicator remains proud of the chain


  • If the longer side of the indicator stays proud of the chain (see figure above), then the chain has not stretched too much, but how much exactly is not clear.

    We need to measure some more with the shorter side.

replace chain soon
Shorter side of wear indicator drops into chain


  • Place one end of the shorter side of the indicator into the chain (perhaps marked '0.75% wear').

    If the shorter side of the indicator will drop into the chain, then the chain needs replacing soon (see figure above). The chain has stretched a little, but not too much

    If the shorter side stays proud of the chain, then the chain has not stretched much at all - it is fine.

 

2. Do you need to replace a) your chain, or b) your chain, cassette and chainring?

Check your cassette and chainrings:

  • does your chain 'kick off' or 'jump off' the chainring at the front, or the cassette of gears at the rear, particularly when you push hard on the pedals?
and
  • are the teeth on your cassette and chainring are worn down into a 'zig-zag', or 'saw-tooth' profile, instead of the original 'half-moon' shape?
  • saw-tooth pattern on worn chainring
    Chains will 'kick off' a worn ring

    If the answer to these questions is "Yes", then, unfortunately, you probably do need to replace all three components at the same time (see Replace cassette page and Replace chainring' page). You did not replace your chain soon enough and are now being punished!

    Check your chain: Before you buy expensive bits, check your chain is running freely. Kinks in the chain, or rust/severe lack of lubrication may also cause your chain to 'kick off' (see Check chain runs freely section on this page)



3. Remove chain

Get chain onto small cogs: Change gear so that the chain is on the smallest cog on the rear cassette and the smallest chainring on the front. A slack chain is easier to work with. Note how the chain is threaded through any mechanism for changing gear at both the front and the back.

split chain by pushing rivet out
Push out rivet


  • Split chain: Place the chain into the central channel of a chain tool or 'Chain Splitter'. Align the pin of the chain tool with the rivet of a link of the chain. Turn the crank handle of the tool so that the tool slowly pushes out the rivet. Then turn back the handle, retract the tool pin, and the chain will be split.

rivet still in outer link plate
Rivet stuck in outer plate


  • If you will be putting the same chain back on, the trick is not to push the rivet out too far - just enough to clear the barrel and for the chain to fall apart, but the rivet is still stuck in the outer link plate. If left like this, the rivet will be a lot easier to push back in.

bicycle chain
Keep the old chain as a guide to correct length


  • Keep the old chain: it's a good guide to the correct length of the new chain.



4. Thread new chain

Thread one end of the new chain through the rear Derailleur mechanism - over the front of the upper jockey wheel, through the hanger and then round the back of the lower jockey wheel. Then thread the other end through the front mechanism. Keep the chain slack by threading over the smallest sprocket of the rear cassette and the smallest chainring.

thread chain back through mechanism
Thread chain through gears


5. Check chain length and shorten if inecessary

responsive image
Push down on the chain to guage the right amount of 'give'

Check chain length:

  • Check smallest run: Over the smallest sprocket ('rear cog') and chainring, a chain of the right length shouldn't hang down by more than 2cm or so when joined. If it 'slaps around', you may need to remove a link or two.
  • Check longest run: Over the largest sprocket and chainring, a chain of the right length will look reasonable horizontal, but will 'give' by 2-3cm when you push down on it.
  • Check most gears: In most gears, the rear Derailleur arm should hang close to the vertical.

Decide if you need to shorten your chain:

If yes:

  • identify the link(s) to remove. Check that the chain ends you will be left with are compatible e.g. if your new chain has a connector link then you'll want two, closed ends.

  • Then, use the chain tool as before to push out the rivets. Take care not to shorten your chain too much - is a lot easier to take links out, than add links in.



6. Join ends together

There are two ways of joining chain ends - special 'connector' links or a rivet

supalink
Connector link


  • Re-usable links or chain connectors come in two halves. Put a half-link on one end of the chain, and the other half-link on the other end.

align ends of chain
Press connector link together


  • Then join the two halves of the link together, and pull the chain ends apart. Hear it click and it's joined!

push rivet back in
Push rivet back through barrel


  • Turn the chain tool round so that the chain tool pin is on the same side as the rivet sticking out of the chain. Then place the two ends of the chain in the tool, with the barrel end of the chain between the open link plates of the other end of the chain.

  • Align the pin head of the tool with the rivet, the hole in the outer link plate and the hole through the barrel. Mmm ... fiddly! Then screw in the pin to close the chain. If the chain is not lubricated already, oil it now.



7. Check chain moves freely

Test your new chain: Pedal gently, and attend to the chain closely.

  • Can you hear any clicks or see any jumps as the chain passes through the Derailleur?

  • Can you see any 'kinks' or 'humps' in the chain as its moves (see figure)? The chain may even 'kick-off' the gears, particularly under pressure.

 
kink in chain may cause chain to brea
Stiff links cause chain to 'jump'


  • Pushing the rivet back in may also squeeze the plates together, creating kinks in your chain.

    Identify which rivet is causing the problem, and then widen the link

loosen joint by bending plates apart
Force plates of stiff links apart


  • Try inserting a screwdriver into the link and then rotating the blade, forcing the link plates fractionally away from the barrel.

    Or place your thumbs on the sticking link and attempt to bend the chain laterally (sideways, rather than up and down).

 

Results


results
Feel more directly connected to the bike with a new chain




Bike Fixer

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"mc" grew up car-free in the countryside, and had to ride a bike from an early age - absolute magic! In later life, he survived London traffic and l'Etape du Tour.


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