Replacing a chainset is a fairly simple modification that can be made to your bike in a short space of time. Some people replace the chainset for an upgrade or for other reasons such as; worn teeth on the chain rings, worn out bearings in the bottom bracket, changing from a 52-39 ratio to a compact chain set or just because of cosmetic damage.

The newest style of chainsets made by Campagnolo, Shimano, SRAM and after-market suppliers such as FSA are very similar in design. None of them use a traditional bottom bracket which is a heavy unit containing the axle and bearings in one unit. The rend now is to use oversized bottom bracket cups which contain the bearings and have chainsets with a fixed axle on the drive side of the chainset. Campagnolo is a slight variation in that they have half the axle on each side of the chainset and the two halves mesh inside the frame. The benefits are reduced weight, less potential for play in the various connections and ease of maintenance.

Removing an old-style chainset

We've dismantled a Campagnolo square taper chainset and bottom bracket for this demonstration but all the old-style systems follow a similar method although each will need specfic tools to match the bottom bracket unit; Campagnolo, Octalink (Shimano) or Isis. In addition to these you'll need an 8mm Allen (hex) key, a crank puller to remove the cranks and a suitable spanner (or an adjustable) to fit the puller.

If you have the luxury of a bicycle workstand fix the bike to it now to make life easier for yourself. The stages for removing the Campagnolo chainset are:

1. Drop the chain off the smaller chain ring and rest it on the bikes frame.
2. Remove the crank arm retaining bolt using the 8mm Allen key.
3. Install the crank puller and nip up with a suitable spanner.
4. Now turn the crank puller to remove the chain set and crank arm from the bottom bracket.

The body of the crank puller screws into the hole left where you removed the crank arm bolt and then the inner part of the tool pushes against the axle of the bottom bracket to remove the chainset. Some more recent Shimano Octalink chainsets have self-extracting bolts and don't need a crank puller tool.

The same process is applied to the non-drive side of the chainset to remove that crank arm.

A Chorus chainset in all its carbon glory. Remove the crank bolt first on both sides with an Allen key. The cap hides the thread that the crank puller screws into.
Thread in the crank puller and then tighten up with a spanner. Now screw in the central part of the tool and the crank is forced off the axle.

Removing an old-style bottom bracket

Removing a bottom bracket is a relatively simple process but before you start it is best to find out whether you have an Italian

threaded bottom bracket or an English threaded bottom bracket. An Italian bottom bracket may be identified if it has '36 x 24' written on the cups, the difference here is that both threads will be right handed! [If in doubt check with the bike manufacturer's website or your local bike shop.]

With an English threaded bottom bracket the drive side (that's the side with the chainrings on) has to be turned CLOCKWISE to remove the bottom bracket cup. On the non-drive (just the crank arm) the bottom bracket needs to be turned COUNTER-CLOCKWISE to remove the bottom bracket cup.

To get the bracket out you'll need the appropriate bottom bracket tool; Campagnolo, Octalink or Isis, a suitable spanner (or an adjustable), a spare wheel skewer, gloves (unless you like grease) and some rags and a cleaning agent like GT85.

With the bottom bracket used in the photo sequence the non-drive side (left) needs to be removed first. Note the flange on the right side which obviously won't go through the frame! The sequence is as follows:

1. Insert the splined bottom bracket tool fully into the cup, hold in place with the wheel skewer. Remove by turning the adjustable spanner counter-clockwise.
2. Once the cup is fully out, remove the bottom bracket cartridge.
3. Insert the splined tool in to the right hand (drive) side and remove in the same way as the left (non-drive) side, remember to turn the spanner clockwise to remove. [See note above about what to do it you have an Italian BB.]
4. Clean the threads thoroughly with a rag and GT85.

The drive side of the bottom bracket has a flange, you'll have to remove the other side first!	Use the skewer to hold the BB tool in place
Rotate the spanner anti-clockwise to remove the non-drive side	The drive side undoes clockwise.

Fitting a new-style chainset

As the new-style chainsets don't have a separate bottom bracket the whole fitting process is much quicker and simpler. Again, depending on the manufacturer you'll need slightly different tools but in general you will need a bottom bracket tool, a tension cap tool, a suitable Allen key (normally 5mm), grease or anti-sieze and gloves to keep your hands clean. Ideally you'll also have a torque wrench for the final setting of the pinch bolts.

To fit the bottom bracket cups follow these steps:

1. Apply grease or anti-seize to the threads of the bottom bracket.
2. Select the correct cup for each side of the frame; they will be marked R for the drive side and L for the non-drive side.
3. Twist the right cup into the frame by hand, turning COUNTER-CLOCKWISE.
4. Tighten with the bottom bracket tool.
5. Twist the left cup in to the frame by hand, turning CLOCKWISE.
6. Tighten with the bottom bracket tool.
7. Take the drive-side chainset, normally the one with the axle fitted, grease the axle and push it through the right-hand cup.
8. Fit left crank arm onto the other end of the axle, it will only fit one way!
9. Apply grease to the tension cap, fit into the left arm and loosely tighten by hand (to 3NM) and spin to test. The crank should spin freely, if it is tight loosen the cap.
10. For Shimano chainsets (and others that use pinch bolts) tighten both of the pinch bolts evenly, one then the other until tight. Tighten the pinch bolts to between 6 and 12 NM.

You can now set the chain onto the chain rings and test out the gears. Fit the pedals and enjoy!

A big hole through the frame!	No, this isn't a bottom bracket, it's just a sleeve to keep the axle clean. The drive side goes in first.
Greasing up the non-drive side bearing cup.	The arrow reminds you which way to turn, and the 'R' which side it should be screwed into.
You need a special spanner.	Slipping the new chainset on, the axle is bonded into the drive-side crank.
Tightening the non-drive crank, FSA use a splined axle so there are no pinch bolts on this chainset.	Make sure the cranks are properly aligned!