Our regular series of articles on basic bike mechanics continues with Phil Walker taking a look at changing a cassette and chain, something that you really ought to be able to do yourself.

The chain and cassette is an area of the bike that needs to be maintained properly for the gears to work smoothly and, most of all, safely. If either the chain or cassette is worn you will experience slipping or jumping gears and poor shifting, especially under load when climbing or sprinting out the saddle.

If you were to look at a worn chain and cassette you would probably not notice any wear, this is where it is useful to have a chain wear indicator in your toolbox - examples like the Park Tool CC3 are dead easy to use and effectively just tell you 'worn/not worn' which is perfectly adequate. A worn chain can easily break which could lead to a serious injury. Just a few simple checks will tell you if the bike is safe or dangerous to ride.

Important

When replacing a worn chain the cassette should be replaced at the same time. If you don’t, the chain will potentially skip over the teeth on the cassette under load. It is important to replace any worn components with correct replacement parts; eg, 9 or 10 speed chain and cassette. If you don’t feel confident working on your bike and you don’t have the correct tools for the job, it is best not to attempt this task.

Cassette removal

You'll need the following tools to remove and re-fit a cassette: a chain whip, a cassette removal tool (specific to the type of cassette you are removing) and a spanner. Because old cassettes tend to be really dirty you'll also benefit from some disposable gloves, degreaser and rags!

Secure the bike, ideally in a workstand, and remove the rear wheel and then remove the skewer (taking care not to lose those little cone springs...). Take the cassette removal tool and fit it into the matching slots in the end of the cassette and then replace the skewer through the tool and the axle but don't fully tighten it - it's only there to stop the tool falling out! You can get cassette tools with stub axles already fitted which provide an alternative way of ensuring it stays in place.

You now need to fit the chain whip onto the teeth of the old cassette so that it rotates in a clockwise direction - the chain whip will be used to stop the cassette just going round and round when you try to undo it.

Now fit the spanner to the cassette remover and rotate it anti-clockwise while holding the chain whip against the pressure. The locking ring should be tight so don’t be afraid to use some force until loosened off. A loud 'zip' noise will be heard when it loosens off.

You can now remove the skewer and fully remove the lockring. At this point it's worth dropping the whole of the old cassette into a bag to keep the grease and gunk away from everything. Clean up the freehub body with a rag soaked in degreaser and then re-grease in preparation for re-fitting the new cassette.

Cassette installation

Tools needed to re-fit a cassette are the cassette remover and spanner and some grease. In an ideal world you would do it up with a torque wrench but most people just rely on using a decent sized spanner and a bit of grunt!

When fitting the new cassette be careful to fit all spacers and shims included. Pay special attention to which shim goes where, you definitely don't want any bits left over! Slide each cog (sprocket) onto the freehub body, both Shimano and Campagnolo cassettes are 'keyed' so that each sprocket will only fit in one position - you may have to check the location of the key each time if you aren't familiar with the process. The red dot in the picture highlights the smaller key slot on a Shimano cassette. Repeat until the whole cassette is fitted.

Now apply a small amount of grease to lockring threads and screw the lockring into the freehub body to clamp the sprockets in place. Now fit the cassette removal tool and the skewer but this time make sure the skewer is tight against the removal tool. Using the spanner, turn the cassette removal tool clockwise until it is tight. If a torque wrench is used, tighten to 40 Nm. Spin the cassette, check for smooth operation. There should be no lateral movement and all the sprockets should be tightly clamped onto the freehub body.

Chain replacement

Removing a chain is a simple process but there are a few guidelines to follow to make it more straightforward. You'll need a chain tool, sometimes called a chain breaker or splitter, a replacement pin for the type of chain you are using and some disposable gloves - chains get really gunky!!

It is important to remove the correct pin when splitting the chain, failure to do this will result in a weaker chain. Always elect a chain pin that is identical to adjacent pins, do not attempt to remove previously removed pins or any pins that look different to the others or you could be introducing a weak spot into the chain.

Place the chain into the chain tool, align the driving pin with the selected rivet on the chain and turn the handle on the chain tool until it stops, keeping it at a right angle to the chain. Normally the pin will still be engaged in the chain plate. Now back off the chain tool and remove it from chain.

To separate the chain fully, hold each side of the protruding pin and bend the chain towards the protruding pin whilst gently pulling on chain to separate the links. Remove the chain from bike and bag it with that old cassette, be careful not to cover yourself in oil!

Fitting a new chain

When you unbox the new chain you will always find that it will be longer than the chain you removed. For the gear system to work correctly the new chain should be shortened to the same length. Shortening the chain is very similar to removing the chain, see the above instructions. Take into consideration that there are inner and outer plates so double check before you remove any links.

Guide the chain over the smallest front chain ring, over the cassette, then through the jockey wheels on the rear derailleur. Make sure that the protruding pin is facing away from you.

Lift the chain off the front chain ring and let it hang over the bottom bracket. This will give you more slack when connecting the chain together. Pull the two ends of the chain together. Slide inner plates into the outer plates and align holes, the protruding pin should hold chain together.

Now take the special connecting pin, lubricate the tapered end and insert it into chain until it touches the old protruding pin. Back the chain tool off enough so the chain can fit into the cradle and then wind the new pin into the chain until it looks identical to every neighbouring pin. If the old pin had been left in the outer plate the new pin will have pushed it out, throw this old pin away.

Before you continue make sure that you have pushed the pin far enough in. The chain will now have the tapered end of the new pin protruding away from you, this needs to be removed before the bike is ridden. Use the chain removal tool or pliers to break the taper off the new pin, simply twist it sideways. Check chain pin alignment again and then check links for tightness. Loosen any tight links by twisting the chain carefully.

You can now re-hang the chain on the front chainrings and, assuming that you measured up correctly, all the gear indexing should work correctly. Your final action is to re-lubricate the chain - although they are always pre-lubed it's only a thin coating to protect them in storage and transit.

Phil's top tip

If you are intending to remove the chain on a regular basis for transporting purposes you will weaken the chain greatly. A great way around this is to use a Connex chain or a Connex quick release link. With this link you can remove a chain in a matter of seconds. They are compatible with both Shimano or Campagnolo chains.