BICYCLE AUTOPSY TUTORIAL
Figure 1 - A typical steel suspension mountain bicycle
Building custom bicycles is a great hobby that can be learned by anyone with a desire to create. The skills needed to dismantle, alter and repair bicycle components can be easily learned, and the parts and tools you will need are quite inexpensive. Discarded or worn out bicycles offer many good parts and can often be found at local scrap yards, city dumps, or yard sales for a few dollars. Even if you plan to build a custom creation using all new parts, this hobby will seem inexpensive compared to many, as you can purchase a brand new bicycle with decent components at a store for less than a hundred dollars.
The great thing about hacking and welding bicycles is that you will be working with all steel components, which are much stronger, more common, and much less expensive than high grade aluminum or carbon fiber bicycle parts. If you have never torn a bicycle apart before, then this basic introduction will show you all you need in order to complete a total bicycle autopsy in minutes, stripping an entire cycle down to the individual parts using only a few basic hand tools.
There will be some very useful tips and tricks presented that may save you a lot of frustration, especially if you are just starting out, so read through this entire section before embarking on any of the upcoming projects.
Figure 1 shows the most commonly available and inexpensive mountain bike available today, the all-steel frame suspension mountain bike from the local hardware store. This cycle cost me $120, and was used to make the StreetFox tadpole trike. The components are medium quality, and include aluminum rims, cantilever brakes, and suspension on both the front forks and rear triangle. Because the frame is made of steel, it can be easily cut and welded using any welder.
Often a bicycle like this can be found at a yard sale for a few dollars, although there may be a bit of rust on the frame, worn out tires, and the odd seized brake cable, nothing that we can’t easily fix or replace. OK, now grab your toolbox, and let’s tear this bicycle down to the individual parts.
Figure 2 - Front component details
Starting with the front of the bicycle, Figure 2 shows the parts that you should get to know by name. As per the letters, the components are:
A) Handlebars, gooseneck, brake levers and shifters. Handlebars are held in place by the clamp on the gooseneck and are available in many widths and heights. Often, a mountain bicycle will have straight or slightly curved handlebars such as these ones, whereas a road bike will have “curly” handlebars which allow the rider to hold on in two positions - a relaxed upper position, and a more aerodynamic “tuck” position. The gooseneck fits into the forks stem, and is held there by a wedge, which will be shown in greater detail later on. Goosenecks are available with two common stem diameters, so make sure you don’t put the smaller sized gooseneck into the larger sized fork stem, or it will not be completely secured.
B) Head tube and fork stem. The head tube is the part of the frame that the fork stem is inserted into. The two cups on the top and bottom of the head tube carry the fork bearings, and will be shown in greater detail later. Head tubes are available in two common diameters, which means that there are also two common sizes of head tube cups and bearings. Again, always ensure that the parts are the same size, or there will be excessive friction in the steering system. There is no common standard for the length of the head tube, or the length of the fork stem, so you should keep matching parts together as a set as you collect them.
C) Front forks. Front forks come in a vast array of sizes, shapes and styles, ranging from the most basic straight leg style to the ultra heavy duty triple tree motocross style forks used for downhill mountain bikes. The front forks will fit only one size of front wheel properly, and the most common sizes for the bicycles you will be working with are; 26 inch, 24 inch, and 20 inch. Most modern front forks will also include the front brake mounting hardware such as the one shown in Figure 2.
D) Front brakes. The front brakes are the most important brakes on most bicycles, as they do the most work. Modern bicycles have cantilever brakes installed on the front forks, but you may also find some brakes that connect to the front forks using a single bolt through the crown of the fork. The type of brakes that connect to the fork using a single bolt are caliper style brakes, which are much less effective than the cantilever style shown in Figure 2 due to the fact that they do not exert as much friction on the front rim.
E) Front wheel. Bicycle rims are available in many sizes and styles, but the 26-inch rim with 36 spokes is by far the most common wheel for an adult sized bicycle. Extremely cheap rims are made of steel, do not have stainless steel spokes and should be avoided due to poor braking characteristics and strength. 20-inch diameter wheels are often used for children’s bicycles and freestyle BMX bikes, and they can have as few as 26 spokes and as many as 48. BMX wheels with 48 spokes are extremely strong, which is why they are often chosen for trikes or load carrying cycles.
F) Front hub. The front hub will have spoke hole drillings to match the rim, with 26 holes being the most common number of spokes for an adult bicycle. Decent quality hubs are usually made of aluminum, but you will most likely find both steel and aluminum hubs in your scrap pile. The hubs contain a pair of ball bearings to allow the hub to spin with minimal friction around the axle.
G) Front dropouts. The front dropouts are slotted tabs on the front forks that allow the front axle to drop out of the forks once the nuts are loosened. Unlike the rear dropouts, the hole is not slotted, so it is not used to adjust the wheels position in the forks. There is usually a small hole above the axle slot where a special tabbed washer can help lock the front wheel in place in case one of the axle nuts comes loose.
H) Top tube. The top tube runs from the head tube to the seat tube and is normally under compressive load on a bicycle frame. The top tube is usually the second largest diameter tube in a bicycle frame.
I) Down tube. This tube runs from the head tube to the bottom bracket and is under tensile stress in a bicycle frame. This is normally the largest tube in a bicycle frame, and one of the most important in the strength of the frame.
J) Seat tube. This tube is normally the same diameter on all bicycle frames as it has to carry the seat post, which fits snug inside the tube. The top of this tube will also have some type of clamp which will tighten around the seat post, allowing it to lock in place at the desired height. On a suspension bike frame, this tube may or may not have the duty of carrying the seat post. On the frame shown in Figure 2, it does not.
Figure 3 - Rear component details
The most common components you will find at the rear of a bicycle are shown in Figure 3, and as per the letters, the components are:
A) Suspension gusset. This part may differ depending on the style of suspension, but its basic purpose is to transmit the forces from the suspension spring into the frame in a way that does not induce damage on the frame. Typically, this part will be made from two steel plates with a thickness of 3/32 inches. The top of the rear suspension spring will be held between the plates by a hollow bolt.
B) Suspension spring. The rear suspension spring includes a high tension coil spring as well as a gas filled shock absorber so bumps and vibration are not transferred from the wheel into the frame. The spring is typically rated for 500-800 pounds of compression, which is due to the mechanical advantage gained thanks to the position of the fulcrum on the rear triangle. A high quality rear suspension spring may have 3 or 4 inches of travel and cost more than a thousand dollars. The ones you will typically find on inexpensive bikes will have less than 2 inches of travel and cost only a few dollars to replace. The top ring is usually adjustable to offer a minimal amount of control over spring tension.
C) Rear triangle. The entire moving part of the rear suspension is called the rear triangle. On any bicycle frame, this assembly includes the seat tube, seat stays (M), and the chain stays (L). The three parts actually form a triangle designed to carry the rear wheel. This assembly is extremely strong.
D) Rear brakes. Much like the front brakes, rear brakes are available as cantilever style brakes as shown in Figure 3, including the mounting studs directly on the seat stays, or as bolt on caliper brakes of lesser quality.
E) Cantilever brake studs. These studs are welded directly to the seat stays and allow the brake arms to pivot, placing the pads against the rim. It is best to not remove the brake studs, as their alignment is somewhat critical to proper brake operation.
F) Front derailleur. The front derailleur forces the chain to move between the two or three front chainrings by derailing it slightly at the top as it enters the chainring. The two plates that are on each side of the chain rub directly on the chain to force it to move.
G) The chain. A bicycle chain is available in several sizes, although the pitch remains the same. A single speed bicycle chain is the widest style of bicycle chain, and is quite rigid from sided-to-side as it does not have to run through a derailleur. BMX bikes and those with coaster hubs have a single speed chain. A bicycle with a derailleur must have a thinner, more flexible chain due to the fact that the chain does not always make a perfect parallel run from the front chainring to the rear freehub. A derailleur compatible chain is quite flexible from side-to-side, and is offered in various widths depending on the number of gears on the rear free hub.
H) Front chainrings. The front chainrings have between 20 and 50 teeth, usually having two or three on a crankset for a full range of gears. The front derailleur will move the chain between the chainrings to switch gears as the rider pedals forward. The smaller gear makes you pedal faster but delivers more torque to the rear wheel (for climbing) whereas the large chainring makes you pedal slower, but propels the bicycle at faster speeds.
I) Crank arm. Normally made of aluminum, the crank arm connects the pedals to the front chainrings so the rider can pedal the bicycle. The crank arms must convert reciprocation motion to rotary motion, much like the piston rod in a petrol engine. Crank arms are available as a left and right unit that connect to an axle like the ones shown in Figure 3, as well as a single piece style crank arm, which is shaped like a large S, having both arms connected as a single unit.
J) Pedals. Offered in many varying styles and shapes, the pedals thread directly in to the crank arms and allow the rider to put force down on the crank arms. Pedals have a left and right side, with the right side (chainring side) having standard clockwise threads, and the left side having reversed threads. Pedal threads are also available in two standard sizes, the smaller size is used on three-piece crank sets and the large size is used on single piece crank sets.
K) Crank set axle. The crank set axle is only available on a three-piece crankset, and must fasten the two crank arms together. We will examine these parts in more detail later.
L) Chain stays. These two tubes run from the bottom bracket to the rear dropouts on each side of the rear wheel. These tubes are part of the rear triangle.
M) Seat stays. These two tubes run from the top of the seat tube to the rear dropouts on each side of the rear wheel. These tubes are part of the rear triangle, often including the rear brake studs.
N) Rear freewheel. The rear freewheel is a collection of small chainrings built onto a one way clutch. When the freewheel turns clockwise, the rear hub turns with it. When the freewheel turns counterclockwise, the hub does not turn with it, which is why a bicycle can coast along with the cranks not spinning constantly. The effect of gear sizes is exactly the opposite of the front chainring, with larger gears offering more torque, and small gears offering faster speeds. Most freewheels have between five and seven chainrings. To calculate the number of total gears on a bicycle, multiply the number of chainrings on the front crankset by the number of chainrings on the rear freewheel.
O) Rear dropouts. The two slotted plates at the junction of the chain stays and seat stays are designed to hold the rear axle in place, and offer a bit of adjustment for the rear wheel. Because the slot extends for an inch or more, the rear axle can be moved along the slot, allowing the rear wheel to be adjusted slightly. On a single speed bicycle, this adjustment is used to pick up any chain slack. The rear dropouts also hold the rear derailleur in place.
P) Rear axle. The rear axle is a threaded rod that contains the rear hub bearings, cones, and rear axle nuts. On some bicycles, the rear axle also clamps the rear derailleur to the frame by placing it between the right side dropout and the axle nut.
Q) Rear derailleur. Much like the front derailleur, the rear derailleur must force the chain to move across all of the rear freewheel chainrings in order to switch gears. The rear derailleur must also pick up chain slack, which is why is has a long body containing two idler gears on a spring loaded axle. The chain has a lot of slack when it is sitting on the two smallest chainrings, due to the fact that it does not have to travel as far as it does on the larger rings.
Figure 4 - Rear derailleur and chain details
The rear derailleur pulls the chain around the rear chainring as shown in Figure 4. Because the chain must keep tension no matter which chainring it may be on, the derailleur body must pivot back and forth to pick up the chain slack. The chain must also come in contact with at least half of the teeth on the chainring or it may skip, which is why the upper guide wheel is directly under the rear axle.
The point labeled C in Figure 4 shows the two small adjustment (limit) screws which control how far the derailleur can travel along the rear freewheel. If these screws are not set correctly, the chain may fall off the largest or smallest chainring, or fail to reach them. The chain on the top of the chainring is called the drive side chain (A), as it is always under tension when the cycle is being pedaled. The return side chain (B) is never under any tension as it simply returns back to the chainring.
Figure 5 - Removing the front wheel
Remove the front wheel by loosening the two axle nuts so it can fall out for the fork dropouts. Of course, you must first release the front brake pads, or the wheel will become stuck between the brake pads and the front tire. Letting out all of the air in the front tire will also work, but simply releasing the front brake pads is much easier.
As per Figure 5, press the brake arms together so the cable head can be removed from the brake arm slot (D). Also shown in Figure 5 are the cantilever studs (A), which have built in return spring so keep the brake pads (C) away from the rim when not in use. The brake pads can be adjusted for different rim style by moving them along the brake arm and then locking them in place with the brake pad bolts (B). Properly adjusted brakes should not rub on the rim when idle, but sit as close as possible to the rim.
Figure 6 - Removing the rear wheel
The rear wheel will come free from the rear dropouts once the rear axle nuts are loosened and the rear derailleur is pulled back as shown in Figure 6. Standing the bike upside down on the handlebars and seat makes maintenance a lot easier.
Figure 7 - Removing the chain
The chain can also be removed from the frame by taking out one of the links. A chain breaking tool (Figure 7) is highly recommended, as it is inexpensive and extremely useful, especially if you plan to build some of the projects that require longer chains.
Figure 8 - Removing the rear derailleur
The rear derailleur is held to the frame either by the rear axle nut or by its own bolt threaded into a tab on the frame. Before it can be removed, the shifter cable must also be removed by loosening the locking nut as shown in Figure 8. Also shown in Figure 8 is the cable end cap, which can be pulled off the end of the cable using a pair of pliers.
Figure 10 - Removing the pedals
Do not forget about the left hand thread on the non-chainring side of the crank set, or you will be hammering on the wrench all night without any success! If you forget, simply look at the backside of the pedal stud, where you will find an L or R stamped on to indicate which pedal you are working on. As shown in Figure 10, the L indicates a left side pedal, so you turn the wrench clockwise to loosen it.
Figure 11 - Removing the crank arms
The crank arms on three-piece cranks set are fastened to an axle by a bolt through the centers. As shown in Figure 11, the small plastic cap must be removed in order to get to this bolt. If the cap is slotted, it will unthread using a large flathead screwdriver. If it is just a cap, then pry it off with a screwdriver blade.
Figure 12 - Removing the crank axle bolt
The crank axle will either have a nut or a bolt, but both threads are normal threads, so the wrench will turn counterclockwise to loosen the part. Figure 12 shows the socket wrench used to remove the bolt.
Figure 13 - Removing the crank arm
The crank arm may be another stubborn part to remove, especially of some corrosion has built up between the axle and the crank arm. Use a long bolt, or some type of steel wedge to help bang off the crank arm as shown in Figure 13. The wedge should always be placed in the crank arm and not the chainring, or the thin chainring will be bent. Again, a little heat via the blowtorch may make a really stuck crank arm budge.
Figure 14 - Removing old handle grips
Usually, handle grips can be removed by forcing them off from the inside edge. Of course, they may be glued on, or so stuck that you have to use the “ugly method” of removal as shown in Figure 14. A single cut with a razor knife will get them off every time, but they are going straight in the trash can after that.
Figure 15 - Removing handlebars and gooseneck
The handlebars are held in place by the clamp at the end of the gooseneck, and can be removed by loosening the nut as shown in the upper half of Figure 15. You will need the handle grip and levers removed from at least one side of the handlebars so they can slide through the clamp before removing them completely. The actual gooseneck is held into the fork stem by a wedge shaped nut that is released by turning the bolt in the center of the gooseneck as shown in the lower half of Figure 15.
Figure 16 - Removing the gooseneck
A common "newbie" mistake is to loosen the gooseneck bolt as shown in the last photo, then start cranking the handlebars left and right, while trying to lift the gooseneck from the fork stem. Because of the way the wedge shaped clamp locks in place, simply loosening the bolt in the center of the gooseneck will not always free it. You must tap the bolt down about ¼ inch after loosening it as shown in Figure 16 in order to free the wedge.
Figure 17 - The wedge shaped gooseneck clamp
As you can see in Figure 17, the wedge shaped clamp will slide along the angled cut, creating a tremendous amount of friction in the fork stem, holding the gooseneck in place. Often you can completely remove the long bolt and still have the wedge stay securely fastened in the fork stem, which is why the tapping of the bolt head is necessary. Also, there are two common sizes of gooseneck stems, so do not put the smaller size in the larger sized fork stem or you may not get a good lock.
Figure 18 - Removing the seat and seat post
Removal of the seat and seat post is nothing special – just loosen the nut that holds the clamp around the seat tube to release the seat post. It is best to leave the seat installed when you take out the seat post, this way, you can use it as a place to hold on to as you turn the post around while pulling upwards on the seat. Figure 18 shows the loosening on the nut around the seat post clamp.
Figure 19 - Removing the front forks
The front forks have a threaded stem and are held in place by a threaded bearing race, a lock washer, and a top nut. The top nut can be removed by turning it counter clockwise as shown in Figure 19. The lock washer and bearing race will usually come free by hand, as they are not supposed to be very tight. The lock washer has a tab, so it must be lifted straight off of the fork stem, and the bearing race will unthread just like the top nut.
Figure 20 - The fork bearings
The fork bearings will fall out of the head tube cups once the forks have been removed. As shown in Figure 20, the bearings have two sides, a ball side and a ring side. Always place the bearing in the cups balls first, or they will not work properly. A stiff fork that does not spin freely is a clear sign of an improperly installed or wrong size bearing in the head tube cups. Yes, there are several sizes of bearing and cups, so keep the same parts together.
Figure 21 - The fork hardware
The fork hardware is shown in Figure 21. There will always be two bearings of equal size, a bearing race (larger ring), a lock washer (thin ring), and a top nut. Again, the bearings, cups and races must all match, so keep them all together as a set when salvaging bike parts.
Figure 22 - Removing the head tube cups
Often, you will need to remove the head tube cups to weld or cut a head tube. Simply bang them out from the inside of the head tube as shown in Figure 22 using some scrap steel rod or a long bolt. A few taps on each side of the cups should set them free with little effort.
Figure 23 - Head tube cups have a top and bottom
The head tube cups shown in Figure 23 have two different heights. The larger cup is for the bottom of the head tube and the smaller one is for the top. If you put them in backwards, the fork hardware will not work correctly, and the forks will seem very stiff when they are turned.
Figure 24 - Removal of the rear suspension spring
The rear suspension spring is held in place by the gussets on the frame and rear triangle by a pair of hollow bolts. Simply find the appropriate sizes hex keys, and remove the two bolts as shown in Figure 24. Don’t worry, the spring is not under any tension and will not go flying around the room once it is freed.
Figure 25 - Removal of the rear triangle
If your frame has rear suspension, then the entire rear triangle will come free from the frame by removing the bolt that holds it onto the pivot tube. This pivot is also fastened by a hollow bolt that requires a pair of larger hex keys to undo as shown in Figure 25. You may have to tap one of the bolt halves out with a hammer once releasing the first bolt.
Figure 26 - The rear suspension pivot hardware
Figure 26 shows the rear suspension pivot parts once they are removed. The small tube that is welded to the frame has a pair of plastic plugs that act as a bearing surface for the pivot bolt, so don’t forget to tap them out if you plan on welding or cutting this tube. Some higher quality suspension frames may actually have a bearing in place of the plastic plugs.
Figure 27 - Taking apart the bottom bracket hardware
To remove the bottom bracket hardware, start by loosening the locking ring on the left side of the frame by turning it counter clockwise as shown in Figure 27. This ring locks the bottom bracket bearing cup in place, and should be easy to remove by tapping on the slot with a hammer and chisel or by using a pipe wrench to grab it.
Figure 28 - Removing the bottom bracket hardware
Once the locking ring is removed, the bottom bracket bearing cup will also unscrew from the left side of the bottom bracket shell in the counter clockwise direction. This cup will probably have a face that can be held with a wrench, and may require a bit of force to turn. When you free this cup, the two bearings and crankset axle will be freed as shown in Figure 28. Just like the fork bearings, it’s always balls into the cups, not the other way around. Also note that I never remove the right side cup from a bottom bracket, as this cup has a reversed thread and is a real pain to get out. There is usually no reason to remove it, and by leaving it in place, you never accidentally try to install a bottom bracket in reverse or thread the wrong cup into the wrong side.
Figure 29 - Scrounging for bicycle parts
Once you get bitten by the bicycle building bug, you will want to increase the size of your junk pile so you can spend more time building and less time scrounging. Head to the local dumps and see if there is a “good neighbors’ corner” or metal recycling area. Check your local scrap yards, flea markets, auctions, and yard sales.
Tell all of your friends and family that you take all metal scrap, especially bicycle parts, and before you know it, your garage will have a wonderful pile of junk for you to work with. I am lucky enough to have a metal scrap pile at the local city dump, where I can easily find 10 or more bikes every day I visit, but even if you have to dig around for junk, it doesn’t take very long to accumulate a huge collection of parts. Figure 29 shows a typical day at my favorite hardware store – the city dump scrap pile.
Figure 30 - The grinder is your best friend
An angle grinder is a must for this hobby. This simple and inexpensive tool will be your most used weapon, and can reduce a frame into its individual components in minutes. You will also want three kinds of discs for your angle grinder - standard grinding discs, zip discs for cutting, and sanding (flap) discs for cleaning up welds, paint, and stickers. Figure 30 shows the trust angle grinder removing the excess material from a freshly severed bottom bracket.
Figure 31 - Some more grinder handiwork
If you plan to build your own custom frames, then you will need the basic building blocks. You could actually purchase new frame components, but I hear that this is extremely expensive, and have never done so myself. It just seems silly to spend a hundred bucks on a few bottom brackets when I can find 10 of them for free at the dump, then hack them from the frame in a few minutes with an angle grinder. Figure 31 shows a completely hacked up mountain bike frame, each part labeled as follows:
A) Down tube
B) Top tube
C) Seat tube and seat post clamp
D) Seat stays and rear brake studs
E) Chain stays
F) Head tube
G) Bottom bracket
H) Rear dropouts
With these basic building blocks and some spare metal tubing, you can build any project, and many more that only your evil imagination can conjure up.
Figure 32 - This device will turn you into a building guru!
With a pile of scrap bicycle parts at your disposal, and an angle grinder ready to slice and dice, all you need is the magical box shown in Figure 32, and you will be a garage hacking guru. Seriously, for about $200, you can purchase a basic welder from a local hardware store and learn how to weld in less than a week. I have seen many new builders ask about purchasing a welder in our builder’s support forum and then that same person will send me a photo of a completed bike a couple of weeks later – it’s like magic. You can make all Atomic Zombie projects using the most basic welder money can buy, and I actually use a department store AC welder for all of my work.
Every single project on our website was made with nothing more than a $200 department store welder, and angle grinder, and piles of bike parts. I only weld with 6013 rod using an AC stick welder, and do not even own a drill press, so there is no reason why anyone can’t build all of the projects. If you really want to become a master of the arts, then you can take a welding course, which is usually only a few weeks long, and will teach you the finer points of welding. So if you are just starting out, head down to the welding supply house and tell them you want a decent beginners welding rig that will plug into whatever power source you have in your garage that will allow you to weld thin walled tubing.
Figure 33 - Here is your battle gear
In addition to that basic welder, you will need a box of rod or wire (depending on your choice of welder), a pair of decent work gloves, a chipping hammer, welding helmet and of course, some type of eye protection.
Again, let me emphasize that I only own a very basic AC welder, an angle grinder, and the gear shown in Figure 33, yet there is probably no vehicle I cannot build with these tools. I have no drill press, lathe, tube bender, or chop saw, so if I can make these cool machines, then so can you. With a little practice, you will be able to create a show room custom, and have the ability to turn your wildest imagination free, creating one of a kind custom vehicles that rival any of the mass produced department store bikes available. So, get that welder plugged in, collect a pile of junk and get to work!
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