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Guide to Bicycle Technology (article index)
In the present section, those parts will be described that are commonly used in several different locations on the modern bicycle. Included are descriptions of their operation as well as detailed instructions for their maintenance, which will eliminate the need to repeat these details for each of the individual applications in subsequent sections. The following details will be covered here:
There are a number of other common details that apply not so much to the maintenance as to the manufacture of the bike. Since these are nevertheless of importance when it comes to judging the quality of bike or components, these details will be covered in Section 4. Screw Threaded Connections Most components of the bicycle include some kind of screw threaded connection. This not only applies to conventional nuts and bolts, but also to the attachment of individual parts to the bike and the internals of minor items, ranging from ball bearings to cable adjusters. Consequently, an appreciation of their operation is necessary for all maintenance and repair work on the bicycle and its individual components. Simple though these things may seem, a more thorough understanding is essential for your own safety. This was recently confirmed by a German survey that showed the likelihood of an accident due to an incorrectly installed or attached accessory is three times as high for items mounted by the cyclist as for those in stalled by a bicycle mechanic. In the US and Britain, the situation is probably quite similar. Yet it is easy enough to learn to do it right. 3.1. Screw thread details 3.2. Dura-Ace gruppo. These are Shimano’s top road racing components. Fig. 3.1 shows the parts of a typical screw threaded connection. It comprises a cylindrical (male) part with a thread in the form of a helical ridge wrapped around the circumference and a hollow (female) part with a corresponding groove. The outside diameter of the male part is just a tiny bit smaller than the inside diameter of the female part measured at the deepest point in the ridge, so the male part fits inside the female one without undue resistance when it is turned until the components that are to be connected (e.g. the Once the male part is screwed fully into the female part head of a bolt and the face of a nut) make contact, the resistance suddenly increases as the surfaces of the threads are pushed hard up against one another over the entire helical contact surfaces of the thread. The resulting friction is adequate to firmly hold the connection. If there is some obstacle to the mutual turning before this point is reached, e.g. when the threads are dam aged or dirty, the resistance becomes so great that it may be impossible to reach the point where contact forces hold the connection properly. For this reason, screw threads must always be cleaned and preferably slightly lubricated before installation, and parts with damaged thread must be replaced — or in some cases a damaged thread can be re-cut by a bicycle mechanic with the appropriate thread cutting tool. 3.3. Thread locking devices Locking Threaded Connections However firmly attached to begin with, many threaded connections come apart after cycling due to vibration. This applies most notably to parts that are attached in only one place, since this causes an imbalance aggravated by vibration. For this reason, care must be taken to attach accessories in two or more locations whenever possible, and to frequently retighten single attachments — or use at least two mounting points. In order to minimize the effect of vibrations, several locking devices have been developed, some of which are shown in Fig. 3.3: locknut, locking insert nut, spring washer and lock washer. The latter is shaped to match a longitudinal groove cut in the male part to accept the inward pointing key on the washer. Another solution, that cannot be shown in any illustration, is the use of a locking adhesive, such as Locktite. Although all these solutions work to some extent, even these have to be checked and retightened regularly. In the case of the locknut, the inner nut must first be tightened independently, after which the outer nut is tightened against the inner nut. 3.4. Shimano Dura-Ace track racing gruppo. When tightening or loosening screw threaded connections, accurately fitting tools with correct leverage must be used to provide the right torque. Excessive torque can damage parts, while too little torque leads to inadequately tightened connections (or, when trying to loosen a connection, would not suffice to do so). Some manufacturers specify the torque that should be used, which can be controlled by means of special torque wrenches. For the home mechanic, it will generally be sufficient to make sure tools of the right size are used. Sizing and Leverage of Tools Screwdrivers must match the size of the saw cuts or the size of the cross-shaped recess in so called Phillips- head screws. Allen keys of the exactly matching size must be used on bolts with hexagonal recesses. Use open-ended wrenches or (preferably) box wrenches that exactly fit on hexagonal nuts and bolts. When using two tools that do not have the same leverage (measured as their handle length perpendicular to the axis of the connection) use the tool with the longer lever on the part to be moved, the shorter one on the stationary part. Wrenches are supplied with Increasing handle size as their nominal sizes go up to provide correct leverage. Fastened by hand, with the correct size wrench perpendicular to the axis of the connection, the chance of damaging the connection by overtightening is minimal. When using an adjustable wrench, select a short one for small nuts, a larger one for larger ones to prevent excessive torque. To loosen a particularly stubborn connection, apply penetrating oil, such as WD-40 to the threads before resorting to tricks to increase leverage (e.g. by means of a length of steel tubing stuck around the handle of a wrench). Ball Bearings Bicycles and their individual components, ranging from wheel hubs to cranksets and from pedals to the head set, largely owe their smooth running properties to the use of ball bearings. These were invented around 1865, initially specifically for bicycle applications. The use of exactly spherical hard steel balls, embedded in lubricant between the fixed and the rotating parts of the bearing assembly reduces the resistance enormously. The most common type of ball bearing on the bicycle is• the adjustable cup-and-cone model, depicted In Fig. 3.5. In this type of bearing, the balls lie between a cup-shaped outer race and a conically shaped inner race, one of which can be adjusted in- or outward by means of screw thread. The cone is the adjustable part on wheel and pedal bearings, whereas on most bottom brackets it is the cup that is adjustable. 3.5. Adjusting parts of cup-and-cone bearing. 3.6. Bearing loading situations Lubrication can be in the form of oil or grease. Al though oil has the advantage that it rinses out the wear and dirt particles, it must be replenished frequently and is rather messy. Consequently, bearing grease is almost universally used these days. On Wilderness Trail Grease-Guard mountain bike components (also available from SunTour under license), clever V-shaped seals isolating the inside of the bearings makes it possible to grease each bearing through a separate grease nipple, providing the same advantage as oil lubrication, but without the mess. Bearing Maintenance Ball bearings must be adjusted correctly: they should have minimal lateral play yet rotate freely. To establish whether a bearing is loose, check whether a point with some leverage connected to the rotating part stays in place when applying lateral force relative to a point connected to the fixed part (thus, to check a wheel hub bearing, push and pull the rim relative to the fork blade or the rear stays). Tighten the bearing if free lateral movement is noticed. To find out whether the bearing is too tight, check whether it can be rotated freely. If it feels rough or if there is noticeable resistance, it is either too tight or, more likely, damaged. Loosen it first and then check again: it should be overhauled if it either does not reduce friction or results in lateral looseness as described above. Although a worn bearing may seem to rotate freely when adjusted just a bit loose, that is not the solution, because the situation will change radically once the bike is loaded, which explains the some times mysterious high resistance on bearings that seem to rotate freely when unloaded. 3.7 and 3.8. Wilderness Trail Grease-guard fitting and matching tools for grease injection. A chevron-shaped seal prevents grease from going where it shouldn’t. The way bearings are loaded varies quite a bit depending on the location. Relatively simple are those of the wheel hubs being loaded perpendicular to the axis, which is referred to as radial loading. The headset bearings of the steering system are loaded in line with the axis, referred to as axial loading. Pedals and bottom brackets are loaded asymmetrically. Fig. 3.6 schematically shows the various loading cases and the particular bearing designs that are most suitable for each. Unfortunately, this is something too few manufacturers take to heart, with the result that even today few bikes run as smoothly as a 1932 BSA, which used bottom bracket and hub bearings of the type illustrated in Fig. 3.9, now offered only on the exclusive French Maxicar hubs. 3.9. Detail of adjustable precision bearing as used on Maxicar hub. Adjustable Bearing Maintenance To overhaul an adjustable bearing, disassemble it and replace both the ball bearings, which are usually contained in a bearing ring or cage, and any other parts that show signs of wear in the form of irregular grooves, pitting or corrosion. Then fill the bearing with clean grease, reassemble and adjust. The bearing cage must be installed in such a way that only the bearing balls, not the metal of the cage, contacts the surface of cup and cone. The adjusting procedure is given below. Overhauling and other maintenance instructions applicable to the various specific bearings will be provided in the sections of Part II. The following description outlines the principle of bearing adjustment in general, assuming the cone is the screwed (i.e. adjustable) part, while the cup is fixed. Adjust Bearing: 1. Loosen the locknut by one or two turns, while countering at the underlying cone. 2. Lift the locking washer to free the cone. 3. To reduce play in the bearing, screw the cone in slightly — perhaps V8 turn at a time, while countering at the opposite locknut. 4. To loosen the bearing (rarely necessary), unscrew the cone slightly, while countering at the cone on the other side. 5. Push the locking washer back onto the cone. 6. Tighten the locknut while countering at the under lying cone, making sure it does not turn. 7. Check and repeat if necessary. Cartridge Bearings In recent years, more and more manufacturers have re- placed conventional cup-and-cone bearings by non-adjustable cartridge bearings, often referred to as sealed bearings. These units, shown in Fig. 3.10, are not adjustable but tend to be more accurate, less prone to wear, and easier to seal against penetrating dirt. Their theoretical disadvantages are their reduced load bearing capacity for the same overall size and the need to replace the entire unit in case of wear. In practice they usually hold up very well. 3.10. Cartridge (sealed) bearing Wedge Connections This method of attachment is used in various locations on the bicycle by means of matching tapered or conically shaped surfaces. Typical applications of this method are found in the attachment of the cranks to the bottom bracket spindle and the handlebar stem to the front fork. The principle of the wedge connection is that a given axially applied force transfers a much increased lateral or radial force when applied via a slanted surface, proportional to the slope. The maximum connecting force is thus achieved by choosing the angle of the wedge surface relative to the axis as small as practicable. 3.11. Principle of wedge connection Since, on the other hand, the relative displacement increases inversely proportional to the slope, the parts must be made more accurately matching and of less deforming materials as the angle is made smaller. This applies especially to the connection between cranks and bottom bracket spindle, while the situation is much less critical in the case of the handlebar stem attachment. When wedge connections come loose, it is mainly because the deformation of one part relative to the other increases the play, thus reducing the contact pressure. This applies mainly to cheaper components, made of relatively soft materials and short contact surfaces. Any wedge connection, especially when new, must be tightened frequently — once a week or before every long ride during the first month. This prevents damage done by a loosening connection and keeps the connection trouble-free without need for frequent tightening from then on. Another important precaution is to clean and slightly lubricate the contact surfaces, which prevents seizing. Bowden Cables Brakes and gears are usually activated by means of Bowden cables, so named after their inventor Frank Bowden, the founder of the Raleigh bicycle factory. As depicted in Fig. 3.12, a Bowden cable consists of a flexible but unstretchable stranded steel inner cable and a flexible but incompressible outer cable constructed of a helically wound flat steel strip, usually plastic-coated on the outside. The inner cable takes up tension forces, while the outer cable is used to counter these by taking up compressive forces. 12. Bowden cable details A nipple is soldered on at one end of the inner cable — usually the end that is connected with the operating lever. At the other end it is clamped in by means of an eye bolt or a pinch plate. The outer cable is usually finished off at both ends with a metal bushing or ferrule and is restrained at a fixed anchor point. Generally, cables work more accurately when the inner cable is relatively thick, while the outer cable must be very tightly wound. To check their quality, it will suffice to make sure the former does not stretch under force, while the latter must not compress. Cables used in conjunction with indexed gearing systems usually have a low-friction internal sleeve between inner and outer cable, which makes operation even smoother, while the use of stainless steel inner cables tends to improve things by preventing corrosion and increased friction. The routing of the cable is critical. Comparative tests conducted at a German technical university proved that the bending radius is of little effect and can be kept quite tight (a radius of 5cm, or 2 inches, is adequate), while the overall length should be minimized, commensurate with unhindered operation of the cables and associated mechanisms. It will also be advantageous to run as much of the inner cable free between relatively short sections of outer cables, rather than enclosing the full length of it in outer cable, as has be come the fashion. The maintenance-free cables with liner for index gearing systems have double-stranded outer cables that are very hard to cut. Consequently, they are usually sold in fixed lengths exactly corresponding to a particular combination of derailleurs, shifters and anchor points. Other cables are generally sold separately: inner cables to be cut down to the correct length, and outer cable by the yard. All cables must be kept clean. Those without internal low-friction sleeve should be lubricated — use Vaseline before installation and enter oil at the points where the inner cable disappears into the outer cable a couple of times yearly afterwards. 3.15. Campagnolo Centaur component group for mountain bike use. Beautifully shaped and finished, it is slowly taking its place besides Shimano’s and SunTour’s top gruppos. Cable Care The two locations that must be inspected for damage on the inner cable are where the nipple is attached and where the other end is clamped in. Replace any inner cable on which individual strands are broken, since friction is increased and sudden breakage may occur. On the outer cable, the thing to watch out for is that it is never pinched or abruptly twisted, since this restricts the internal diameter locally, leading to so much friction that reliable operation is defeated. 3.14. Shimano Deore XT mountain bike component group. Included are a choice of sever al different brakes and the easy shifting Hyperglide freewheel with matching chain. Although the particular set shown here is a few years old, it is updated regularly and remains Shimano’s top-of-the-line mountain bike gruppo. When replacing a cable, cut the outer cable off very carefully to prevent forming an inwardly protruding hook at the end. The outer cable must be cut off about 3cm (1¼”) outside the clamping point, using a special sharp tool that does not cause the ends of the cable to fray. It is recommended to solder the inner cable strands together around the point where it will be cut before doing so, which makes it easier to cut and prevents cable fray for good. To do this, heat up the cable with a soldering iron and then allow some resin core solder to melt at the point where the tip of the soldering iron touches the cable, waiting for the solder to run around and in between the strands before removing the soldering iron. Adjusting gears and brakes usually amounts to changing the tension of the cable. All systems in which Bow- den cables are used include an adjuster, shown in Fig. 3.13, to compensate for wear and real or apparent cable stretch. The (excellent, though in the US rather uncommon) hub gear mechanisms by Fichtel and Sachs use a variation on this theme that uses a grooved pin and a clamp instead of the screw threaded pin and the matching adjusting bushing with locknut. Cable Adjustment Procedure: 1. Establish whether the inner cable should be tightened (after some wear or use) or loosened (only the case if parts have been replaced). 2. Where possible (on brake cables), un-tension the cable by loosening the quick-release or by unhooking the transverse cable. 3. Hold the adjuster bushing and loosen the locknut by several turns. 4. Holding the threaded pin, screw the bushing further on or off, as appropriate to increase or decrease cable tension, respectively. 5. Holding pin and bushing, tighten the locknut up against the former. 6. If appropriate, reconnect cable or tension quick release. 7. Check operation and repeat if necessary. Quick-Releases These handy mechanisms are frequently used to ease installation and removal of such parts as the wheels and the seat, while a similar device is often used to tension or un-tension the brake cable. Folding bikes may have a similar mechanism to latch the two parts of the frame into place and ease folding them together. Essentially, any quick-release is based on the eccentric cam principle, which allows applying considerable force over a short range of travel by means of a hand- operated lever via a cam that is arranged eccentrically with respect to its pivot point. Figures 3.16 and 3.17 show the principle and the operation of a typical quick- release mechanism, as applied to the hub in this case. 3.16. Principle of quick-release 3.17. Operation of quick-release When operating a quick-release system, a few points must be kept in mind, namely: 1. The lever should not be used to screw the system in but only as a lever that is twisted fully to tighten or loosen the assembly. 2. The locknut or thumbnut at the opposite end is not used to tighten it, but only to adjust the system until the length of the assembly is exactly right to allow definite loosening and tightening of the lever by hand. 3. Install the levers in such a direction that they run more or less parallel to a frame member, such as the seat stay, so the latter provides a restraint for the hand when operating the quick- release and so the lever does not protrude excessively. Working on the Bike When carrying out repair and maintenance work on the bike, it is recommended that you support the bike in a rack designed for that purpose. Some excellent examples of home-mechanics’ work stands are the Black burn Sportstand and the model offered by Tacx, both of which are small and light enough not to be in the way when not in use and cheap enough to keep the average cyclist’s budget intact. For those who like the home-made touch, we have included a drawing of a handy device that is easily made in Fig. 3.18. This handlebar stand is particularly useful for people who do not really intend to do too much work on the bike themselves or those with very limited space. It is used to support the handlebars of the bike when placed upside-down, thus preventing damage to cables and controls and providing a reasonably stable hold. 3.18. Simple handlebar support Selecting Tools Although we’re not giving a list of tools here, specific tools for each of the operations discussed in the guide are listed with the instructions. It will be wise to start off with a very basic kit comprising sets of screw drivers, Allen keys, open-ended wrenches, box wrenches, two adjustable wrenches, a small hammer and the tools needed for fixing a tire. All other tools may be purchased as the need arises. When buying tools for working on the bike, always select the highest quality available. Generally that does not mean those that shine the brightest, but those that are the most expensive. Don’t be fooled by terms such as ‘economy tools’, because only the best (i.e. expensive) tools provide real economy. Cheap tools are inaccurate and easily deformed, causing damage to the bike in addition to their inherently poorer performance. My own experience is that the most expensive tools are invariably worth their money if you get serious about maintaining the bicycle. Most of the common tools are best bought at specialized tool or hardware stores, while the specific bicycle tools listed in subsequent sections should be bought only at a bike shop. Although we don’t in general recommend patronizing mail order companies except if you don’t have access to a bike shop, the limited availability of tools at most bike shops may force you to make an exception when it comes to buying tools. Nashbar and JensonUSA are two reputable specialist tool suppliers, and their catalogs and web sites are gold mines of useful information on tools and working procedures. 3.19 and 3.20. Left: Work stand from Tacx. Right: Full set of special bicycle workshop tools. Such sets are available from VAR and Campagnolo. The thread cutting parts must be spec for English, French or Italian threading. |
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