The crank set is the collective name we give to the system of components made up of the cranks, which are the metal "arms" that connect your pedals to the rest of the drive train. The bottom bracket, which is the axle and bearing system, that allows the cranks to rotate freely within your frame. Finally, the chain set made up of a number of chain rings.
The purpose of the crank set is to transfer your pedaling power to the remainder of your bikes drive train system i.e. rear cassette, front and rear derailleur etc.
You should regularly check your cranks and chain rings, particularly if you ride off-road; to make sure they're in good physical condition. You should also check your bottom bracket to make sure there's no "play".
Got a problem? Get the answer
The main problems experienced with the Crank set are:
- Damaged cranks
- Worn or damaged chain rings
- Play in the bottom bracket bearings
All crank set problems can be serious and it is usually best to have the bike checked by a competent cycle mechanic. Our guidance therefore concentrates on procedures that are relatively simple to perform.
Simple checking procedure
Inspect your cranks and chain rings visually, looking for cracks, dents or other signs of damage. Also check your chain rings for general cleanliness. In the event of you finding damage, whilst a "bent" chain ring can sometimes by straightened with the use an adjustable hand wrench, a damaged crank should be replaced immediately.
To check the condition of your bottom bracket bearings, grab hold of either crank and rock it back and forth perpendicular to your frame.
Movement or "knocking" may suggest that the bearings need to be adjusted, are damaged and need to be replaced, or the crank bolts are loose.
Crank set Cleaning Procedures
- Clean completely whenever you wash your frame. Each time you clean also check carefully for hairline cracks.
- Regularly clean the grime and dirt build-up off your chain rings, using a stiff brush and solvent when necessary. To get into those hard-to-reach places, a screwdriver wrapped in a clean rag or one soaked in degreaser is ideal.
- When cleaning your bike keep the bearings in your bottom bracket as dry as possible. Watch out for those jet washers, they can force water where it shouldn't go.
Removing and replacing a modern chain set
- Most chain sets have dust covers to protect them. They come in two types. The plastic ones you can remove with a screwdriver. The more expensive bikes, however, have caps that screw into place.
- Once the dust cap is off, you will need an extraction tool. On one side of the tool is a socket wrench. You need this first. Make sure it fits snugly over the crank bolt. Now, use a spanner or adjustable wrench to loosen it.
- Once the bolt is loosened, you can unscrew it the rest of the way with your hands. Make sure you didn't leave a washer inside the crank.
- Now you need to make sure the threads on the crank and on the extraction tool are not damaged. If not, screw the extractor into the crank.
- The extractor should screw in easily within 5 or 6 turns. If it takes less than that, remove it and start again as you probably have it twisted.
- Once you have it straight, gently tighten the extractor with a spanner or adjustable wrench. Now screw the shaft of the extractor in by hand and then use a spanner or wrench and get it firmly into place.
- It takes a lot of force to loosen a crank, so, if for some reason it becomes easier suddenly, stop and check everything. The crank is either loose or, you are damaging something.
If you have a really good bike, the chain set is often removed by unscrewing a central Allen bolt alone.
Removing and replacing chain rings
When you are reassembling crank bolt, consider using Loctite adhesive to help retain the bolt
All chain rings are bolted onto the spider with chrome Allen bolts. Undo one of the bolts a half-turn, then, undo the next one similarly, and so on until all are loose enough to remove by hand. Many of these Allen bolts attach through a sleeve extending through the chain rings and the spider.
- You can detach the outer ring by gently puling on it. Now slide it up the pedal arm. Make sure there are no spacers and then lift it away.
- Many times you will need to remove the sleeve nuts before you can take off the other chain rings.
- Sometimes, the inner chain ring will be attached with a separate set of bolts. Undo these in the same manner as described above.
Before you can replace a chain ring you need to remove the chain set from the bottom bracket. See elsewhere.
Removing and replacing a cotter pin chain set
- First you need to undo the nut and washer on the cotter pin. Now, give the cotter pin a good thump with a hammer. If that doesn't push it out, try using a small metal bar and place that on the pin. Then hit it again.
- If the pin isn't damaged (but it probably will be), you can reuse it but we would always suggest using a new one.
- First try to fit the new pin into the crank arm. If it doesn't fit, gradually file the pin down, trying it every so often.
- The pin should stick out of both sides of the crank arm equally.
- Make sure the nut is under the crank when the crank points backwards.
- Use a hammer and lightly tap the pin into place, then put the nut and washer in place.