The bottom bracket is what allows your cranks to turn. If your cranks are wobbly, or there's a noise coming from between your cranks when you pedal, then you may need to overhaul your bottom bracket.
This instructable (a remix of FriendofHumanity's 'ble) will show how to remove, clean, lube and adjust most adjustable bottom brackets using only common hand tools and one "special" tool.
What you need:
- Channel lock pliers
- Needle-nose pliers
- A socket wrench
- A screwdriver
- A towel
- A crank puller (The "special" tool. One size fits all. $14 on amazon here.)
Step 1: Identify Your Bottom Bracket
First, you need to make sure you have an adjustable bottom bracket.
What does this mean? Well, there are two types of bottom brackets: adjustable bottom brackets and sealed cartridge bottom brackets. If you have problems with a sealed cartridge type bottom bracket, the only solution is to replace it. If you have problems with an adjustable bottom bracket, you can probably overhaul it and get it running like new.
So what kind do you have? The easiest way to tell is by looking at the left side of the bottom bracket. Find your left pedal. The left pedal is attached to the left "crank", the metal arm that turns when you pedal. The point where the left crank joins the frame of the bike is where the left side of the bottom bracket is.
Adjustable bottom brackets will have some kind of lock ring, maybe with a few slots on the outside or a thin area for a wrench.
Cartridge type bottom brackets will be all one piece, with no lockring, and often with internal "splines" (slots for teeth to engage on the inside).
If yours is adjustable, this instructable is for you. Read on.
Step 2: Understand Your Crank-Puller
To get to the bottom bracket, you need to remove the cranks.
Cranks are attached to bike by being wedged onto the tapered ends of the "spindle" (or axle) that goes through the center of a bottom bracket. Being wedged on means that they're hard to get off without a special tool called a crank puller. Removing a crank without a crank puller would be kind of like pulling a nail out of a board with your bare hands instead of a hammer or crowbar.
So what is a crank puller? Basically, it has three parts, which I'll the "handle", the "crank grabber", and the "push pin".
- Handle: You hold it.
- Crank grabber: It "grabs" the crank in preparation for pulling the crank off of the axle.
- Push pin: It pushes against the axle to pull the crank off of the axle.
The next several steps will show how to remove the cranks with the crank puller.
Step 3: Removing the Cranks Part 1
Cranks usually have a nut, screw, or bolt attaching them to the bike. Remember, the nut/screw isn't actually doing anything to hold the crank on the bike--being wedged on the taper does that--but you still need to remove the nut/screw before doing anything else.
So remove it. Use a regular socket wrench, probably 14mm or 15mm.
Note: Sometimes the nut/bolt/screw is hidden behind a little plastic dust cap. Just pop that off with a screwdriver.
Step 4: Removing the Cranks Part 2
This is how you attach the crank puller to the crank.
- Make sure the "push-pin" is retracted (in other words, make sure that the "push-pin" is not extending beyond the "crank grabber").
- Thread the crank grabber onto the crank. Make sure to screw it all the way in so that lots of threads are engaged. Use a big adjustable wrench to tighten the crank grabber onto the crank.
Step 5: Removing the Cranks Part 3
Turn the handle on the crank puller clockwise (righty-tighty). This extends the "push-pin".
Turning the handle will be really easy at first. Then, when the "push-pin" contacts the taper, it will get really hard, because now the push pin is trying to push the taper out of the hole in the crank. Keep turning. You may need a hammer or cheater bar to get more leverage, especially if the crank's been on the taper for a long time.
Eventually, the pin will push the taper in / pull the crank out, and suddenly you'll be able to pull the crank off the taper.
Rejoice! Then do it all again on the other side of the bike.
Step 6: Remove the Lockring With Channel Lock Pliers
Step 7: Remove the "Adjustable Cup" With Needle-Nose Pliers
The "adjustable cup" is the last thing holding the bottom bracket together.
Usually it has a bunch of holes in it. You can get a special tool to go in these holes (here or here for example). But you can usually get away with using a long pair of needle-nose pliers. Just twist counter-clockwise (lefty-loosy). Usually, this is very easy: all the hard tightening is done by the lockring.
Step 8: Remove the Bottom Bracket Innards... and Get to Know Them
No, my bottom bracket innards did not come out looking this shiny and clean. They were covered in gunk and dirt. Some of the ball bearings had fallen out of one of the housings. I used a rag, a toothbrush, and some WD-40 to clean them up. You could also throw them all in some paint thinner or kerosene to soak for a while to make cleaning them a lot easier.
Once you've got them clean, look at what you have. Identify the parts. See how everything goes together.
Basically, there are two sets of ball bearings. The ball bearings usually fit in some kind of plastic bearing housing. The left-side set of bearings will end up trapped between the adjustable cup and the left side of the spindle. The right-side set of bearings will end up trapped between the fixed cup (which is still on your bike) and the right side of the spindle.
Park has a nice little diagram here that shows all the parts of a typical bottom bracket.
Step 9: Clean Up Inside the Tube Frame and Fixed Cup
The fixed cup is still on the bike. It will hold the right set of bearings.
You can take it off if you want to, but it has nothing to do with the adjustment, so there's no point if you're not replacing it. Just get a rag in there and clean it up.
Notice that my fixed cup has some pitting. This means I should probably replace it. But I'm too cheap and too lazy, and it seems to be running fine after my overhaul. Someday I'll replace the whole thing with a sealed-cartridge bottom bracket, but today is not that day.
Step 10: Grease the Right-Side Bearings and Replace Them (With the Spindle)
Put some grease (like this for example) on the right-side bearings and slide them onto the right side of the spindle. (If you forgot which side the right and left are, the right side of the spindle is longer, because it has to hold the crank that has the chainrings (gears) on it). The housing should not rub against the spindle, only the ball bearings themselves. This usually means that the more open side of the housing faces outwards.
If your bottom bracket came with a plastic sleeve, as mine did, put that on too.
Then slide the whole thing into the frame of the bike.
Note: You could replace the ball bearings while you've got everything open. They're pretty cheap. I didn't because mine looked fine and I didn't want to wait to order any.
Step 11: Grease the Left-Side Bearings and Replace Them
Add some grease to the left-side bearings and place them on the spindle. Again, put the open side of the housing facing outwards.
Note: You could use more grease than I did. I was being a little stingy in an attempt to keep my camera-handling hand clean.
Step 12: Replace the Adjustable Cup
Add some grease to the adjustable cup (if needed) and screw it back onto the bike frame.
Just finger tighten it. The next step is adjusting it.
Step 13: Adjust the Adjustable Cup and Lock the Adjustment With the Lockring
Adjusting the bottom bracket is the step that requires the most finesse. There are a lot of techniques out there, but it basically boils down to just fiddling with it until you get it right.
You want the adjustable be cup to be as loose as possible with absolutely no play. Then you tighten down the lockring against the adjustable cup to keep the adjustable cup from moving.
What to avoid:
The adjustable cup can be too tight. If it is too tight, the spindle will be hard to turn and the bearings may bind.
The adjustable cup can be too loose. If it is loose, there will be "play". This means that the spindle will be able to wiggle as well as spin. You can check for play by grabbing the spindle and trying to wiggle it and listening for a clicking noise. You can also re-attach the right-side crank to give you a better lever for wiggling the spindle.
Get the adjustable cup in the right position. Then try to hold the adjustable cup in that position with the needle-nose pliers while you tighten the lockring. Most likely the adjustable cup will move a little bit, and your adjustment will be wrong.
Loosen the lockring. Adjust. Try again.
Repeat as many times as you have to until you get it right. When it doubt, make it too tight rather than too loose.
Step 14: Replace the Cranks
This is a lot easier than removing the cranks. Just place the cranks on the taper and tighten the nut/screw/bolt that you removed before. The nut/screw/bolt will push the crank back on to the taper, wedging it in place. Make sure to tighten the nut/screw/bolt well enough to make this happen.
Note: You may be tempted to put grease on the taper so that the crank is easier to remove next time. Don't do it. I've been warned that this can cause the crank to have just a little bit of wiggle on the taper, which can cause wear, which can eventually round the taper/crank, which would mean replacing parts, which would mean money and work, which you probably want to avoid.
Step 15: Enjoy
Your bike will now run much more smoothly.