Tearing Down and Rebuilding a Bicycle

Overview

Building a bicycle from parts is expensive, and the first couple of tries will probably end up ruining a lot of parts. A neglected old bike from a garage sale makes a perfect guinea pig for those first prototypes.

Sheldon Brown’s website has lots of info. Additionally, Atomic Zombie’s books contain info on how to strip bikes apart. I own one of the latter and it’s quite handy when you are learning how to take bikes apart.

Removing Cranks

First, remove the chain. Use a chain tool or a dremel.

Second identify if you have a 1 piece or 3 piece crank set. The bottom bracket is the cylinder that the pedals spin inside. 3 piece crank sets have a piece that goes through the bottom bracket and then each crank attaches to this piece with a nut. 1 piece crank sets… well the cranks and spinning piece are all stuck together inside the bottom bracket.

1 piece: undo one of the pedals while the cranks are still secure in the bottom bracket. You won’t be able to remove the crank from the bottom bracket without a pedal off, and it will be hard to remove the pedal when the cranks are bolted down. The left side is reverse threaded. Then undo the nuts at the bottom bracket. The left side is reverse threaded. Catch all the ball bearings that fall out, and remove the cranks.

3 piece: get ready for some fun. These are often really rusted on. Undo the nuts first. This is best accomplished fixing the cranks somehow; either put a crow bar through the bike frame, put something heavy under a crank, or put the bike in a vise. Next, you need to hammer the cranks off. Place the bike on its side on some wood. Starting with the right hand side first, place a long metal tool through the gears and against the crank as close to the bottom bracket as possible. Start hammering away. It WILL eventually pop off. Flip the bike over when you are done. The next step is to open up the bottom bracket. This can be done with a special tool or an old chisel and a hammer. The bottom bracket side covers are threaded on.

Handlebar Grips

Use an old spoke, small screwdriver or chisel and squirt hand soap or dishwashing soap under the grip. Use the tool and gravity (place the bike on its side) to work the fluid in. The grip should come off really easy now.

Wheels

Wheels are made from a hub (the part in the very middle) and a rim connected with spokes. To interface with the road, a strip of rubber is laid inside the rim and a tire with a tube inside stretched over the rim. Wheels that are driven by a chain additionally have a gear set and either a free wheel or a cassette added on the right hand side. The hub is different for the driven wheel because it contains a thread to attach sprockets.

Warning: if you are going to disassemble a hub, do it in a tub or box the first time around. You will scatter about 9 ball bearings for each side of the wheel and like 50 little ball bearings if you open up a freewheel.

Tires come in different radii and with different tread patterns. Maxxis Slickworms are highly regarded tires but run about $30 each. You can get cheaper tires for about $5. The tubes, which are inflated inside the tire to somewhere between 35psi and 100+ psi, also run about $5. A rubber strip is required between the rim and the inner tube to keep the inner tube from rubbing against screws that hold the rim and spokes together. You can chop up an old tube if the strip is missing.

Hubs are empty cylinders with a lip around each end. The lip contains holes. Spokes are inserted into the holes and bent to go into holes in the rim. They fixed in place with screws at the rim end. On the inner part of each end of the hub are grooves filled with ball bearings. A threaded bolt is placed through the hub, then washers placed on each end and nuts threaded on to keep the ball bearings from falling out. The ball bearings let the bolt spin freely inside the hub. The wheel can then be put inside a set of forks and tightened down with another set of nuts.

Freewheel gear sets are made up of sprockets of different sizes threaded onto a metal cylinder. Actually, the sprockets closest to the wheel itself aren’t necessarily thread on. The smaller sprockets towards the outside are threaded on and hold the other sprockets in place. They are threaded with right hand threads.

Cassette gear sets

Because attaching the gear set to the freely spinning bolt would cause a wheel to be driven, the cylinder that the gear set is threaded onto also has a freewheel threaded on inside. The freewheel itself contains another thread that screws onto the hub. The freewheel allows the wheel to ratchet in one direction, so pedaling backwards doesn’t cause the wheel to lock up while in forward motion. The tool to remove the freewheel/gear set from the wheel depends on the manufacturer. I found that a crowbar fits the pattern inside the center of the gear set, and a large adjustable wrench placed on the crowbar will loosen the gear set from the wheel.

The freewheel is threaded with left hand thread (backwards to the usual orientation). The free wheel looks like a roller blade wheel bearing. It is closed. The top, facing away from the wheel, has two dimples that allow the freewheel to be opened with a spanner wrench or a punch and hammer (if the gears are held in a vise). Remember to turn opposite to the usual direction. Once the top of the freewheel unscrews, be very careful as there are two grooves (one on the top and one on the bottom) or races where tiny ball bearings are placed in the freewheel. These will scatter all over the floor and underneath every piece of furniture within 10 feet.

Chain

Bicycle chain comes in different widths, but similar pitches. The pitch is the distance between the rollers. A large pitch means each link is longer.

Click here to see an illustration

Other applications tend to have much smaller pitches. #25 chain, used for electric scooters, not only has a much smaller width but a much smaller pitch. #35, often used for go karts, has a similar width, but much smaller pitch. The reason why a small pitch is popular is that the teeth on sprockets can be spaced much closer together. This allows higher gear ratios than can be achieved with bicycle chain. The highest gear ratio that can be achieved on a bicycle with common components is about 5:1. Usually this is enough because a human pedaling and a standard 26″ wheel turn at roughly the same speed. Motors turn about ten times faster, so they need much greater gear ratios to mate to wheels. To get a high enough gear ratio using bike chain, the sprocket would have to be humungous.

One other factor to consider is chain articulation. According to Bicycle Science, 3rd ed, sprockets with fewer than 21 teeth have decreasing efficiency because energy is lost in bending the links around the ‘tight’ turn. The book does not state how much the efficiency decreases.

Used chains are often rusted. If they have a master link, they can be removed by articulating the chain at the master link so that the clip on the master link can be easily removed. When straight, the clip does not come off easily and will probably be destroyed if you use pliers. If the chain has no masterlink, it might still be removable by using a chain break tool. This is like a vise for chains. When tightened, a little nail sized bolt presses on the center of the roller, pushing the pin out. Don’t push the pin all the way through, just enough to get the chain off, otherwise good luck getting the pin back in. Finally, the chain can be of the type where the pin is stamped in. These are permanently attached. Just get out the dremel and cut the chain off.

You can revive the chain by soaking it in solvent. I have used liquid wrench before. You don’t need a big tub of it. I have sprayed it heavily on a rag and then cleaned the chain manually. If any links are frozen, work them back and forth with some pliers and then spray the liquid wrench on them. WD40 probably works too.

Cables

Cables are made of braided steel strands. They work by pulling some part of the bike, usually working against the force of a spring trying to pull the other way. The sheath of the cable is made of plastic with coiled steel wire embedded inside. This sheath is really important. Without it, you would need a straight run from the lever used to actuate the cable and the brake or derailleur. Since the sheath has steel inside, and the cable is steel, if water enters the sheath the cable and sheath tend to rust up. It’s possible to squirt WD40 inside and work the cable back and forth to revive it. But if the rust is bad, just move on, because it will take far too much time and WD40 to be economical. A box of cables that outfits a whole bike can be bought for $7 at Walmart.

Brakes

Generally come in several types.

Caliper brakes look like a horseshoe made of two parts. They attach to the forks where the two forks split.

V-brakes have a pad that is attached to a post that is attached to the frame. When viewed from the side, they make a shape like the letter ‘T’. V brakes attach to legs of the fork. V brakes have a little inverted V shaped piece of cable so that the cable from the levers attaches at the bottom of the V. When pulled, both brakes pivot against the rim.

Linear pull brakes use a mounting like v-brakes, but don’t require the V shaped cable.

Hydraulic brakes use a disc attached to a wheel. When the cable attached to the brake is pulled, pads grib the disc.

To adjust brakes, go to the brake lever. At the lever, where the cable enters, will be a bolt with a hole in it. Back this bolt out of the lever as far as it will go without getting loose. Now adjust the brakes so that they are touching the wheel rim. Tighten down all the nuts. Now screw the bolt on the lever back in until the brakes no longer grab the rim. Voila, that’s it, but it usually takes a few tries to get it right.

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