Maintaining your bike is crucial to its longevity and performance. One of the most important components of your bike is the bottom bracket, which allows the crank to rotate smoothly. If your bike has a one piece crank bottom bracket then it’s a good idea to service it once in a while. This is because over time it can become loose or worn, leading to decreased performance or even complete failure. In this article, we’ll walk you through the process of overhauling a one piece crank bottom bracket, including disassembly, cleaning, reassembly, and proper adjustment. With a little bit of know-how and the right tools, you can keep your bike’s bottom bracket running smoothly.
One-piece crank bottom brackets are commonly found on older or entry-level bicycles. These bikes include some BMX bikes, cruisers, and some children’s bikes. However, most modern bicycles use different types of bottom brackets, such as a cartridge, external, or press-fit bottom bracket.
Tools required for servicing a one piece crank bottom bracket
- 32-millimetre headset spanner or a large adjustable spanner.
- Flat-head screwdriver.
- Rubber mallet.
- Pedal spanner.
- Correct size spanner for the wheel nuts. They are usually 15mm but on some BMX bikes they can be 17mm or even 19mm.
- Vice.
- Grease.
- Rags or paper towel.
Preparation
- For BMX or kids bikes, raise the saddle to the minimum insertion mark.
- Turn the bike upside down.
- Loosen the rear wheel nuts, including tug nuts if present.
- Release the chain from the chainring.
- Now remove the left-hand pedal. Refer to our article on how to remove bike pedals if you need help with this task.
Removing the crank and bearings
- Begin working from the left-hand side, where you’ll find a threaded section with a lock ring and adjustable cup screwed onto it.
- To unscrew the lock ring, turn the spanner clockwise (note that the thread is reversed).
- Loosen and remove the lock ring and keyed washer. Note that the washer has a salient that slots into the groove in the thread.
- Now it’s time to remove the adjustable cone. There are two slots on it.
- Use a hammer and flat head screwdriver to loosen it clockwise.
- Once loosen unscrew and remove the adjustable cone.
- Inside the bottom bracket cup is a set of bearings in a bearing cage.
- Use long nose pliers to remove the bearing cage. Taking it out first will facilitate the removal of the one-piece crank.
- Hold the right-hand crank arm and pass the crank through the bottom bracket to remove it.
- Proceed to remove the bearings on the drive side.
Cleaning the bearings and cones
- Once the bearings are removed clean the bottom bracket cups.
- Clean the left-hand cone and bearings as well
- Secure the crank in a vice.
- While cleaning the drive side cone, ensure it is tightly fitted. If it comes loose, it will cause the left-hand cone to loosen as well.
- Fit the flat end of the screwdriver into one of the grooves on the cone to push it clockwise.
- Tap it with a mallet until it stops moving, or if it doesn’t move while tapping, it means it’s sufficiently tight.
Assembling a one piece crank bottom bracket
- Apply fresh grease to one set of bearings and into the right-hand cup.
- Place the bearings onto the drive side cone with the flat side against the cone.
- Insert the crank through the bottom bracket shell.
- Grease the left-hand side cup and bearings, then slide them over the left-hand crank and position them in the cup.
- The side of the cage where the bearings are sticking out should be fitted in the bottom bracket cup.
- Reinstall the cone and tighten it by hand in an anticlockwise direction until it stops.
- Now loosen it by turning it clockwise slightly.
- Put the keyed washer back in place so that the salient slots into the groove in the thread.
- Refit the lockring. It screws in anticlockwise.
- Use a 32-millimetre spanner to tighten the lock ring firmly, exerting pressure on the crank and spanner to ensure it is securely tightened.
Final adjustments to the one piece crank bottom bracket
- Check for any side-to-side movement in the bottom bracket.
- If there is any, undo the lock ring,
- slightly tighten the adjustable cup,
- and retighten the lock ring.
Spin the cranks to check if they rotate freely. If not, you may have overtightened the adjustable cup. - Repeat the process until it feels right.
- With this type of bottom bracket, achieving perfection is challenging, so it’s better to have it slightly too tight than too loose.
- Once the bottom bracket is tightened refit the left pedal.
- Finally, tension the chain and tighten the wheel. We have a great article to help you with tensioning the chain.
If you have tightened the bottom bracket and it still feels off or produces crunching noises, consider replacing the bearings.
By servicing your one piece crank bottom bracket, you can expect improved pedaling efficiency, reduced creaking or grinding noises, and a smoother overall riding experience.
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