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Saturday, October 21, 2006
HOW TO REPAIR A 3 PIECE AND SEALED BOTTOM BRACKET
Well, this is it, welcome to bottom bracket Hell! The lowest, nastiest and filthiest part of your bike, but one of the most important. The bottom bracket holds the axle that not only makes pedal motion possible, but also carries your weight while on the pedals and takes other kinds of too long to mention abuses.
First we'll see how to take a bottom bracket apart and put it back together. Then we'll look at some specifics and do some bottom bracket troubleshooting. It is called a three piece cranck because it has three distinctive parts compared to a one piece crank. There is more then three parts, this moniker refers to the axle and two separate cranks. In comparison with the one piece crank that makes office of both crank and axle.
To take one apart is not that hard, when you know what you are doing and have the right tools. The bottom bracket is one part of your bike that requires a specialty tool and there is no way around that. We are tlaking about the pedal puller. This is the only tool capable of removing pedal cranks. The other tools you'll need are a ratchet with a 14 mm socket, and pair of big pliers and a big flat surface to remove that little plastic cover. I hear you pro mechanics out there screaming and yelling about using pliers to remove any piece of the botton bracket. Yes there are specialty tools for the job and you can buy those at your local bike shop. However, this blog is aimed at people around the world who don't have a ton of money and this way has worked well for me since I began working on bikes. So, with this out of the way, let's proceed.
Removing and repairing a 3 piece bottom bracket
1. Find a big flat something and unscrew the cap off the screw that bolts the crank to the axle. Don't use a small screwdriver, the plastic cover will break inside the crank and you will spend the next hour digging it out.
2. Take your 14 mm socket and ratchet, unscrew the bolt that holds the crank to the axle. Remove the bolt of both cranks(Left and Right). You can squeeze the handle of the ratchet and the crank together like pliers to give you more leverage.
3. Take the puller and screw it's socket inside the threaded hole of the crank. Hold the crank and turn the puller handle clockwise until the crank arm falls off from the axle by itself. Remove both crank arms.
4. Go to the left side and with the pliers firmly held with both of your hands(This is where the pictures differ, I'm taking a picture at the same time.), unscrew the lockring from the bearing cup.
5. Now again firmly with both hands, grab the bearing cup with the pliers and slowly test the resistance. You do not want to slip here since this will definitely strip the thread on that cup. Hold those pliers hard and go slowly, it should get it going within a quarter turn and then you should be able to unscrew it with your fingers. If not, keep on going and be careful. Remove the cup.
6. Remove the axle and bearing crowns from both sides.
7. Remove the right side bearing cup by unscrewing it in a clockwise fashion. The notch are not very wide, so might have to hold the pliers on the cup with one hand and the handles with the other. Go slowly, I've pinched the inside of my hand on a few occasion. Be aware that this cup is often very hard to remove. Again, you can always purchase a specialised wrench just for that purpose. I'm just cheap!
8. Clean and inspect everything. What you are looking for is a clean and even line on the axle and inside the bearing cups. Any pits in that line will damage the bearings and they will eventually self destruct. Replace any parts that need replacing.
9. Regrease everything, the axle, the cups and the bearings. I use regular green axle grease with a touch of white teflon grease. Make sure that everything you've pulled out of that frame is extra clean, including the hole in the frame where it came from. The most minute piece of crap can ruin your repack job.
10. Start by installing the right side bearing cup. Screw it in counterclockwise real tight. Insert the bearings and the axle. Insert the bearings in the left bearing cup and screw on the frame. Screw it until you feel resistance. Test to see if the axle turns freely and tug it up and down to see if there is any play. No play? Turns freely? If the answer is yes to both questions, install the lockring on the left bearing cup.
11. Reinstall the crank arms tightly. I would check them again in a few weeks to be sure. When you think it's tight enough, tighten some more. That's it, you're done.
The sealed bottom bracket
The sealed bottom bracket is the same thing but it is in one piece and the bearings are sealed. You need a special ratchet socket to remove it. You cannot repack or adjust it. If it's busted, you have to buy and install a new one. Some like this type of thing, but I don't. I like to be able to fine tune my bottom bracket axle.
Cotter pin crank arm removal
Some older bikes keep the crank arms on the axle with cotter pins jammed between the axle and a hole in the crank arm. It is held together by a nut. An old bike mechanic taught me the secret on how to remove these. Sorry, I had no cotter pin cranks in stock and can't provide you with pictures of this. Guess you'll have to make it with the written word.
1. Set the crank arm at the 6 O'clock position.
2. Unbolt the nut, remove the washer and reinstall the nut with a 2 mm gap between it and the crank arm.
3. With the crank arm still at the 6 O'clock position, give the bolt a solid wack with the help of a good hammer. If it moves inward, you're ok. Repeat this 2 mm at a time until it comes out.
I don't know why, but it works. If you put the crank arm at the 3 or 9 O'clock position to punch out the pin, the cotter pin somehow jams itself and the only way to remove is to drill it out. This method works 90% of the time. If it doesn't come out, your only option is to take a drill to it.
Bottom bracket troubleshooting, or that cracking noise you hear when pedalling.
Ah yes, that annoying cracking noise when applying power to the pedals. This problem comes to my attention often and the tricky part of it is that you have 3 variables to consider to eliminate it.
1. Check the pedals, if their bearings are loose, this could be the source of your problem.
2. Pedals are ok. Alright, check the crank arms one at a time to see if they move sideways. If one oif them moves and not the other, then it's loose and you need to tighten it up. Take note that when a crank arm falls off by itself, the square inside that holds it snug on the axle have rounded off and it will never stay on however hard you tighten it back on. You must change it.
3. Both crank arms move sideways at the same time. The bottom bracket axle is loose. Unscrew the lockring on the left side and adjust the left bearing cup until there is no movement.
4. If the noise still persist, you might have pitting on the axle or cups. This will call for a complete bottom bracket overhaul. But hey! Now you know how to do that. :)
Until next time, ride safe.