|
Guide to Bicycle Technology (article index)
This section deals with the system of components that transmits the rider’s effort to the rear wheel. It comprises the pedals, the crankset (which in turn is made up of cranks, bottom bracket spindle and chain- rings), the chain, and the rear freewheel block with cogs, or sprockets. Not included in this section is the selection of the sizes of chainrings and sprockets, since this subject will be covered fully in Section 10 for derailleur gearing, in Section 11 for hub gearing. The Crankset Known as chainset in Britain, this unit forms the heart of the drivetrain. It is made up of the bottom bracket (comprising the bearings with an axle, or spindle), the cranks and the chainrings that are mounted on an attachment device incorporated in the RH crank. Al though it is generally sold as a unit of components made by the same manufacturer, a certain degree of interchangeability remains. On bicycles without derailleur gearing, a single chainring is used, permanently attached to the RH crank. Bottom Bracket Bottom Bracket Bearings and Spindle These parts are installed in the frame’s bottom bracket housing. The four different models available are depicted on the following pages. Generally, derailleur bikes and other high-quality machines are equipped with either a BSA bracket or a cartridge type unit, the latter with non-adjustable bearings. The Fauber system, better known as one-piece or Ashtabula crankset in the US, is still found on some utility and BMX bikes. The Thompson bracket is mainly used on some low-end European utility machines. On the BSA bottom bracket, the bearing cups are open towards the center and are screwed into the bracket housing from both sides. The axle is forged out of one piece with integral cones facing out, the bearing balls (usually in retainer rings) lying between cup and cone. The RH cup is screwed in all the way, whereas the LH one is adjustable arid locked in position by means of a lockring. The space between the two bearing cups is usually bridged by means of a plastic sleeve to keep dirt and water out. The BSA bottom bracket is the most universally available type, and consequently recommended for anyone who plans to cycle far from home: In case of damage, it can be repaired or replaced al most anywhere with minimal tools and parts. 9.1. The bottom bracket is the heart of the drivetrain. This is Fisher’s special bearing unit with Shimano cranks. 9.2 and 9.3. Assembly sequence of BSA bottom bracket; Cross section through a BSA bearing. The cartridge bearing, often referred to as sealed bearing unit, is not adjustable, being based on conventional machine bearings, or Conrad bearings (some manufacturers display their ignorance by referring to these things as ball bearings, apparently oblivious of the fact that adjustable bearings also qualify for that name). On most models, it is installed in the bottom bracket as an integral unit and held in position either by means of lockrings (Fig. 9.16) or with circular spring clips (Fig. 9.1). Their design is quite critical, since the fixed bearings used are essentially only suitable to support radial loads, and significant wear and resistance could result if the design does not prevent the application of an axial load when tightening the unit in the bracket. 9.4 and 9.5. Above: Cotterless ‘Glockenlager’. Below: Pressed-in cartridge bearing unit. The Thompson bottom bracket has cups that are press-fit into the ends of the bracket shell with the open end facing out, while the cones installed on the spindle face in. Theoretically, this is the right way of doing it, because the off-set pedaling forces are sup ported most effectively this way. Unfortunately, the construction of this item is generally so hopelessly primitive that any theoretical advantage is more than lost by the practical drawback caused by inadequate precision and the lack of a seal against the penetration of dirt and water. The predecessor of this bearing type, the German Glockenlager (‘bell bearing’) combines the theoretical superiority with a labyrinth seal for protection — and a cotterless crank attachment. Unfortunately, it is now virtually extinct. The Fauber one-piece design is perhaps the most interesting, not on account of its bearings, but because here both cranks and the spindle form one unit (the crank to-spindle attachment causes headaches on all other versions). As is the case on the Thompson bracket, the bearings face the right way here. Similarly, the general quality and sealing is far below par, making this an item that rarely works satisfactorily for very long. All bottom bracket types exist in several different versions. In the first place, the axle length has to correspond to the bracket shell width and the number of chainrings installed. Besides, the way the crank is attached to the spindle comes into play. Cotterless and cottered attachments are each available in different dimensional variants. In addition, the screw thread diameter and other details of the installation in the bottom bracket shell may vary. For BSA and threaded cartridge bearings, there are at least four different standards: English, Italian, French and Swiss. Apart from differences in dimensions, the English and Swiss versions have LH thread on the RH (or fixed cup) side; Italian and French versions have RH threading on both sides, the former otherwise closely corresponding in size and thread details to the English standard, while the French system has dimensions that are similar to those used on the Swiss version. The only foolproof way to avoid mis matching parts is to take the entire old unit to a bike shop when buying replacement parts, although Table 4 gives some guidance. 9.6. Bottom bracket tools Bottom Bracket Maintenance This work is required when the cranks seem to turn poorly — either too tight, too loose or too irregular. The adjustments are made on the LH side. To establish whether the bracket bearings are too loose, try to move the end of a crank in and out relative to the frame. It is too tight, on the other hand, if there is a noticeable resistance when you try to turn the spindle by hand after the cranks have been removed. Unfortunately, if the latter is the case, it usually is necessary to do more than adjust the bearing: you may have to overhaul the whole unit, but adjustment should remain your first step. 9.7. Thompson bottom bracket Adjusting BSA Bottom Bracket Bottom bracket maintenance goes best with special bottom bracket tools (a set of special wrenches to match the lockring and the adjustable cup). In a pinch, you can get by using provisional methods such as a hammer, a punch and a screwdriver, but fitting tools are preferable since they prevent damage and are easier to operate. Refer to Fig. 9.9 for this work. Procedure: 1. Loosen the lockring on the LH side by one turn. 2. Tighten or loosen the adjustable cup by one quarter turn at a time. 3. While holding the adjustable cup in place, tighten the lockring again. 4. Check and repeat, if necessary. If perfect adjustment cannot be achieved, overhaul the bottom bracket bearing, following the next procedure. 9.8. EDCO sealed bearing unit. This model allows lateral adjustment. Overhauling BSA Bottom Bracket Do this if adjusting does not lead to a satisfactory result. To carry out this work, the cranks must first be removed, following the relevant description below. Use bottom bracket tools (including a fixed cup wrench, if necessary), a rag and bearing grease. Procedure: 1. Loosen the lockring on the LH side by one turn. 2. Loosen and remove the adjustable cup on the LH side, catching the bearing balls and the spindle as it comes out. 3. Remove bearing balls (usually in retainer) on the LH side, the spindle and the RH side bearing balls. Also prize out the dust sleeve if installed. 4. Clean and inspect all parts. Replace the bearing balls (complete with retainer or loose, whatever your preference) and any parts that are damaged, worn or corroded. Damage is usually evidenced by pitting or grooves in the contact area. 5. If the fixed RH cup also shows signs of wear, re place it too, unscrewing it to the right if the bike is built to English or Swiss standards, to the left if it conforms to French or Italian standards. When re placing parts, make sure to get matching versions. 6. After thorough cleaning, install the fixed cup, if necessary, tightening it firmly. 7. Fill the bearing cups on both sides with bearing grease and push the bearing balls in. If you use bearing retainers, make sure only the balls, not the metal of the retainers, touch the cones and cups. If loose balls are used, don’t try to put too many in: leave just a little play between the individual balls. 8. Install the dust sleeve, followed by the spindle, the longer end in first (towards the RH side), since that’s where the crank with the chainring will fit. 9. Install the adjustable cup, making sure you don’t lose any bearing balls. 10. Install the lockring 11. Adjust the adjustable cup and tighten with the lockring as described above: loosen lockring, adjustable cup looser or tighter, tighten lockring again while holding the adjustable cup. 9.9. Adjusting detail of BSA bearing 9.10. Adjusting side of Thompson bottom bracket bearing. Adjusting Thompson Bottom Bracket The cranks can remain on the bike. The only tool usually needed is a large wrench that fits on the lock nut underneath the LH crank. Refer to Fig. 9.10. Procedure: 1. Loosen the locknut under the LH crank one turn to the right (LH thread). 2. Turn the dust cap underneath the locknut, while pushing it in: to the left to tighten the bearing, to the right to loosen it. This dust cap has a prong that penetrates a groove in the bearing cone underneath — if it does not work, remove the nut and the dust cap and then turn the cone directly, e.g. with the aid of a screwdriver. 3. Tighten the locknut holding the dustcap in place. 4. Check and repeat if necessary. If adjustment does not do the trick, proceed to overhauling the unit, following the next procedure. 9.11. Assembly drawing of the Thompson bottom bracket bearing. Overhauling Thompson Bottom Bracket Remove the LH crank before starting this work. Tools needed for this work include a large wrench, a rag and bearing grease. 9.12. Thompson adjusting detail Procedure: 1. Loosen and remove the locknut under the LH crank by turning it to the right (LH thread). 2. Turn the dustcap underneath the locknut to the right, while pushing it in, to loosen it. 3. Remove the dust cap, then remove the cone by turning it to the right. 4. Remove the bearing balls in their retainer. 5. Pull out the spindle with the RH crank attached towards the right, catching the bearing balls with their retainer on the RH side. 6. Clean and inspect all parts and replace any parts with damage (rust, pitting or grooves). 7. If necessary, remove the bearing cups by hammering them out from the opposite side, and hammering the new ones into place while protecting them with a block of wood. 8. Fill the clean bearing cups with bearing grease and place the bearing ball retainers inside, orienting them so that only the balls, not the retainer, con tact the cups and the cones. 9. Install the spindle with the RH crank attached from the RH side. 10. On the LH side, make sure the bearing ball retainer is in place, then install the cone, followed by the dust cap and the locknut. 11. Adjust the bearing as described above: loosen lock nut, turn dustcap to the left to tighten or to the right to loosen the bearing; then tighten the lock-nut again. Repeat until satisfactory before installing the LH crank. 9.13. The one-piece bottom bracket; also known as Ashtabula in the US, Fauber in the rest of the world, comes with a continuous crank assembly, so the crank-to-spindle connection problem is eliminated. Adjusting One-Piece Bottom Bracket Being one piece with the spindle, the cranks obviously don’t have to be removed. All you need is a large adjustable wrench. Refer to Fig. 9.14 for this work. 9.14. Adjusting detail of one-piece crank- set bearing. Procedure: 1. Loosen the locknut under the LH crank one turn to the right (LH thread). 2. Lift the lock washer under the locknut to free the cone that lies below it. 3. Turn the cone to the left to tighten the bearing, to the right to loosen it. 4. Put the lock washer back on the cone and then tighten the locknut. 5. Check and repeat, if necessary. If adjustment does not do the trick, proceed to overhauling the unit, following the next procedure. Overhauling One-Piece Bottom Bracket Before commencing, remove at least the LH pedal. Once more, you will need a large wrench, a rag and bearing grease. Procedure: 1. Loosen and remove the locknut under the LH crank by turning it to the right (LH thread); twist it around the crank and remove it. 2. Remove the lock washer, then unscrew and remove the LH cone by turning it to the right. 3. Remove the LH bearing balls in their retainer. 4. Pull out the Z-shaped crank and spindle unit to the RH side, twisting it free. 5. Catch the bearing balls with their retainer. 6. Clean and inspect all parts and replace any parts with damage (rust, pitting or grooves). 7. If necessary, remove the bearing cups by hammering them out from the opposite side, using a big screwdriver, and hammering the new ones into place, protecting them with a block of wood. If the RH cone has to be replaced, unscrew it off the spindle and screw the new one into place, clamping the chainring(s) underneath. 8. Fill the clean bearing cups with bearing grease and place the bearing ball retainers inside, orienting it so that only the balls, not the retainer, contact the cups and the cones. 9. Install the Z-shaped crank and spindle unit from the RH side. 10. On the LH side, make sure the bearing ball retainer is in place, then install the cone, followed by the lock washer and the locknut. 11. Adjust the bearing as described above: loosen LH locknut, turn cone in or out a little, tighten locknut again. Repeat until satisfactory before installing LH pedal. 9.15. Interesting crank unit. This design is from Prof von Osten-Sacken of Aachen Technical University’s Vehicle Engineering Department. Lateral Adjustment of Cartridge Bottom Although the bearings of these units usually cannot be adjusted to compensate for play or wear, at least the screw threaded versions allow something that cannot easily be done with other bottom brackets: their lateral position relative to the centerline of the bike can be adjusted. This makes it relatively easy to correct the chain line (the alignment of chainring and sprocket, which will be covered below). You will need the special lockring wrenches for the unit in question. Just loosen the one lockring and tighten the other one until the bearing unit is moved over sideways into the desired position. The Cranks Except on one-piece Fauber units, the cranks are separate parts that are attached to the ends of the bottom bracket spindle. On older simple bikes, they are held by means of a cotter pin, illustrated in Fig. 9.17. The torque transmitted by the cranks on the connection, calculated as the pedal force multiplied by the crank’s leverage, is quite considerable at this point. Consequently, the force on the connection can be 20 times the cyclist’s pedaling force, and cotter pins, with their small contact area, often come loose. 9.16. Cartridge bottom bracket unit For that reason, a solution is used on high-quality bicycles that increases the contact area between connecting parts. Whereas the contact area of a cotter pin is only about 1cm it is typically 8 times larger on a cotterless crank, illustrated in Fig. 9.18. The spindle here has square tapered ends, matching square tapered holes in the cranks. A bolt, or on cheaper versions sometimes a nut, pushes the crank sideways onto the end of the spindle. When replacing any parts of either the cottered or the cotterless crank assembly, keep in mind that there are several different versions. Cotter pins come in different dimensions, matching different cranks and spindles. Cotterless connections may have slightly different angles for the tapered ends. It would be preferable to match make and model, or at least to refer to Sutherland’s Handbook for Bicycle Mechanics (most bike shops have a copy of this expensive reference work) to make sure parts will match perfectly. An interesting variant of the cotterless connection is the one-key attachment depicted in Fig. 9.19, which does not require a special crank extractor tool but can be operated by means of a simple Allen key (older versions of Shimano and some more recent Campagnolo cranks use this technique, which has unfortunately not become common). Although most cranks have a length of 170mm, measured per Fig. 9.20 from the center of the spindle hole to the center of the pedal hole, long-legged riders may wish to use slightly longer models, short-legged riders will be better off with shorter cranks. Some makes come in quite an array of different sizes between 160 and 185mm, while the cheaper models do not offer much choice. Cottered cranks should always be made of steel, since aluminum is so soft that the hole (which is much smaller than it is on the cotterless crank) would deform and the connection would never hold up. The largest European crank manufacturer paid a high price to learn this after it introduced aluminum cottered cranks in the early eighties. (Recently the same manufacturer proudly showed me an aluminum one-piece crank that holds more promise). Even cotterless cranks could be made of steel and then have the advantage that their connection is very reliable, while aluminum cotterless connections have to be retightened several times on a newly installed one. 9.17. Cottered crank attachment 9.18 Cotterless crank attachment 9.19. One-key cotterless attachment 9.20. Optimum crank length as a function of upper leg length. Apart from the kind of deformation of the hole due to insufficient tightening, the most common problem is a crack extending from one of the corners of the square hole. This is typically a fatigue failure, usually leading to sudden fracture across the crank Another problem is that the crank can get bent in a fall. Don’t try to straighten the crank yourself, since it only works with out damage if you use the right bending tool, which most bike shops have. If the thread with which the pedal is screwed onto the crank gets seriously dam aged, the hole can be drilled out and a Helicoil insert can be installed, essentially providing a new screw thread (Fig. 9.22). The RH crank has an attachment flange for the chainring or chainrings. On cheap, simple cranksets, a single chainwheel may just be swaged (pressed) on, while they are simply inserted between RH crank and bearing on one-piece cranks. On quality bikes with cotterless cranks, the RH crank is a forged unit with a star-shaped attachment onto which the chainrings are held with special bolts, typically following the kind of detail depicted in Fig. 9.21. The bolt circle diameter for superficially similar versions can be quite different. It will be easiest to verify the dimension by measuring the distance between the centers of two neighboring holes, then using the appropriate formula below to establish the bolt circle diameter this dimension corresponds to: 3-hole attachment: BCD = 0.58 X 5-hole attachment: BCD = 0.85X where:
9.21. Attachment details for chainrings to cranks. Crank Maintenance The connection between spindle and cranks may come loose, especially on a new bike or one on which the cranks were recently replaced. Left unchecked, this leads to deformation, eventually making it impossible to tighten the cranks properly. Consequently, they should be fastened on a regular basis (every 25 miles during the first 100) at first, and checked once a month afterwards. To carry out this simple maintenance job, there is a crank extractor tool that corresponds to the make and model of cotterless crank in question (the US manufacturer Park Tools offers one that universally fits all). 9.22. Helicoil adaptor for pedal thread Tightening Cotterless Crank You will only need the wrench part of the crank extractor, in addition to something to fit the dust cap (usually a coin does the trick). On one-key models, use a fitting Allen key, and then you just tighten the Allen bolt — the following description applies to all other types. Procedure: 1. Remove the dustcap. 2. Tighten the bolt or the nut that becomes visible in the recess in the crank, countering firmly from the crank. 3. Reinstall the dustcap to protect the screw thread. Replacing Cotterless Crank For this work you need the entire crank extractor including its wrench (or a separate wrench) as well as a rag and some Vaseline. Removal procedure: 1. Remove the dustcap. 2. Remove the bolt or the nut, countering firmly from the crank (if necessary placing a firm rod between the frame and the crank). 3. Remove the underlying washer (this is an essential step, since the crank extractor will not work unless the washer is removed). 4. Retract the internal part fully into the crank ex tractor and then screw the tool into the threaded recess in the crank as far as it will go, but at least 4 full revolutions. 5. Holding the crank firmly, screw the internal part of the crank extractor in until the crank is being pushed off the spindle (if it does not work, you have probably forgotten to remove the washer). 6. Remove the tool from the crank. Installation procedure: 1. Clean and slightly lubricate the square ends of the spindle and the square hole in the crank, as well as the bolt or threaded stud. 2. Place the crank onto the spindle in the correct orientation (the crank with chainring attachment on the right, both cranks 180 offset). 3. Place the washer in the recess and then install the bolt or the nut. 4. Tighten the nut fully, using the wrench part of the crank extractor and countering firmly at the crank. 5. Check and retighten at least every 40km (25 miles) during the next 160km (100 miles) of cycling. 6. Reinstall the dust cap. 9.24. Use of crank extractor to remove cotterless crank. 9.23. Tightening or loosening cotterless crank. Tightening Cottered Crank Although this type is slowly disappearing on newer bikes, it is still used and has the same advantage as the simple BSA bracket: parts are available everywhere in the world. By way of tools you will need a wrench (preferably a box wrench, which is more likely to grip the nut without damaging it) to fit the nut on the cotter pin, while a hammer or any other blunt object comes in handy too. Refer to Fig. 9.25. Procedure: 1. If possible, support the crank near the spindle and hammer the cotter pin in further. 2. Tighten the nut fully. 9.25. Hammering cotter pin in or out Replacing Cottered Crank In addition to a matching wrench you will need a hammer and something to support the crank, a rag and some Vaseline. Removal procedure: 1. Loosen the nut just so far that the screw thread of the cotter pin lies just below the surface of the nut. 2. Supporting the crank close to the spindle, but keeping the cotter pin free, hammer the pin loose from the side of the nut, preferably protecting it with a block of wood. 3. Unscrew the nut and remove the washer, then push the cotter pin out all the way. Installation procedure: 1. Clean the spindle, the cotter pin and the holes for spindle and cotter pin in the crank, then lightly grease these parts. Replace a damaged cotter pin or nut. 2. Install the crank — the one with the chainring attachment on the right and both cranks 180 offset. 3. Install the cotter pin from the side of the larger hole in the crank. 4. Install the washer and the nut, then tighten fully. 5. To allow further tightening, support the crank near the spindle and hammer the cotter pin in further, then tighten the nut again. 6. Check and retighten at least every 40km (25 miles) during the next 160km (100 miles) of cycling. The Chainrings Depending on the kind of gearing used on the bike, the RH crank will be equipped with either one, two or three chainrings. The choice of the number of teeth will be treated in the sections devoted to gearing, but their installation and maintenance will be covered here. Replaceability criteria include both the construction and the attachment details: bolt circle diameter (covered above) and the number of bolts. 9.26. EDCO Competition crank unit As concerns the quality of chainrings, the best ones are not simply stamped but are machined (sharp contours and a regular, fine groove pattern are telltale signals). Machining allows the use of stronger (i.e. more wear resistant and less easily deformed) aluminum alloys. This is the reason Campagnolo chainrings are usually so much better than superficially similar looking items that cost a little less. Wherever the bolt circle diameter of your cranks corresponds to one of the Campagnolo standards, it may be smart to select these when the old ones are worn. Chainring and sprocket teeth wear according to Fig. 9.27, and the smaller ones wear fastest, as do models with special shaped teeth to ease shifting (actually, the very simple solution of cutting back a few teeth as done on Shimano’s Superglide chainrings does not by itself increase wear, it is merely the use of thinner teeth that does). Wear of chainrings, chain and sprockets is mini mized by selecting the former and the latter with such numbers of teeth that prime numbers (numbers that are not multiples of some other whole number except one) result. This minimizes the repeated correspondence of particular teeth, which is one of the major reasons for wear. Special shaped teeth that are de signed to ease shifting work very well, especially for the less experienced cyclist when new. However, they also wear faster, due to the fact that they are thinner in certain thin points of contact with the chain. The recent introduction of stainless steel chainrings (used as the smallest chainring on some mountain bike cranksets) is a big step forward, since they are much more wear-resistant and not significantly heavier than aluminum chainrings. In the late eighties, there was a craze of non-round chainrings, with Shimano leading everybody into believing they will cycle more efficiently with chainrings that are oddly shaped (and every other manufacturer followed). Today, it is generally agreed that the most efficient shape (if there is any difference at all) is round. This also eliminates the question in just what orientation the off-round chainrings ought to be installed for greatest efficiency (the results of efficiency tests have been different for different riders). If you still have non- round chainrings, don’t worry: the difference is mini mal, once you get used to the slightly unnatural pedaling movement, and you can always change to round chainrings when they are worn. 9.27. Typical wear of chainwheel or sprocket teeth. 9.28. Straightening individual teeth of chainring. Chainring Maintenance Check, and if necessary tighten, the chainring attachment bolts once a month. Prevent chainring wear by keeping chainrings, sprockets and chain clean and lubricated on a regular schedule — once a month plus whenever you have used the bike in inclement weather or muddy or dusty terrain. See the section The Chain for comments on establishing when to replace the chain. To clean the chainrings in the area of the teeth, wrap a rag around a small screwdriver and work around each of the teeth. Straightening Chainring If individual teeth of the chainring are bent, it is often possible t straighten them with the aid of a small adjustable wrench. Follow the general procedure illustrated in Fig. 9.28, but you may generally leave the chainring on the bike. You will have to replace the en tire chainring if a tooth should break when trying to straighten it. If the entire chainring is warped, this will usually be evidenced by intermittent scraping sounds between chain and front derailleur cage. First establish which section is bent which way by slowly turning the cranks backward, while watching the distance between the outside of the chainring and a fixed reference point on the bike. Mark the location of the bend e.g. with a felt pen or chalk. In case of a short sudden bend, it is usually the chain- ring itself that is warped, while a longer, more gradual bend indicates that the attachment spider on the RH crank is deformed, meaning that one of the legs is bent in or out. To correct a bend in the chainring itself, straighten it by forcing a wooden wedge between the chainring and a frame tube (usually the RH chainstay), or between two chainrings. To straighten the attachment spider, give a sharp blow with a hammer against the bent leg in the appropriate direction, and repeat until the chainring runs level. 9.29. Shimano Biopace crankset with off- round chainrings. Nowadays, only the smaller chainrings are given this curious shape, while the larger one is usually round — at least on high-end bikes. The Chain The bicycle chain is a remarkably efficient transmission device. This explains why other, technically more complicated drive systems have never made it to success on the bicycle, however often they have been tried. However, the superior efficiency only applies to a well maintained, cleaned and lubricated chain. Whereas such a chain delivers 95% of its input as output, this figure can drop to 80% for a rusty, dirty, unlubricated chain. All bicycle chains have a link length of 1/2” (measured between two consecutive link pins). The width is measured between the inside of two inner link plates and measures a nominal 1/32” for derailleur chains, 1/8” for non-derailleur chains. Even so, there are some differences in construction resulting in slightly narrower chains, measured on the outside, and sometimes with slightly narrower inside dimensions. These are preferable for use on gearing systems with 7 or 8 sprockets. 9.30. The two types of chain construction The wider ½” x 1/8” chain for the utility bike without derailleur is usually equipped with a master link, or connecting link, to join the two ends. As shown in Fig. 9.31, this device must be installed so that the closed end of the spring link faces in the direction of rotation. Since the master link projects further than the other links, it cannot be used on derailleur bikes, where it would hit the derailleur cages. For this reason, an end less chain is used there, which is formed by attaching the outer link plates of the one end with the inner link plates of the other by means of a regular pin. A chain extractor tool is required to remove, install or shorten such a chain. 9.31. Master link for chain on utility bicycle without derailleur Fig. 9.30 shows the two basic chain designs. On the Sedis design, which is copied by some other manufacturers these days, the inner link plates are shaped to carry out the same function provided by the inner bushings on the conventional chain construction. The Sedis design leads to less wear arid flexing but is not as suitable for most index gearing systems except those of the same manufacturer (e.g. Sedis chains works poorly with SunTour index derailleurs, whereas the similar Shimano chain works very well with the same company’s index derailleurs). The special chains for index shifting usually have bulging link plates. Al though they indeed aid shifting, they tend to stretch under load and often have to be replaced. Chain Line To assure optimum efficiency of the drivetrain, the chain should preferably be straight, with chainring and sprocket perfectly aligned as shown in Fig 9.33. Obviously this is illusory in the case of derailleur gearing, since the various chainrings and sprockets lie side-by-side. The best that can be done is to align the central point between the extreme chainrings with the central point on the freewheel block. Thus, the middle chain- ring should be lined up with the fourth sprocket on a system with three chainrings and seven sprockets. Check this alignment perhaps once a year and when ever new drivetrain components are installed on the bike. Adjustments can sometimes be made by installing a spacer on the rear wheel or by means of lateral adjustment of a cartridge type bottom bracket unit. In extreme cases, the frame’s rear triangle may turn out to be misaligned and can be bent back as described in Section 5. When spacers are used on the rear wheel, note that this affects the alignment of the wheels and it may become necessary to re-tension the spokes of the rear wheel in order to line up both wheels. 9.32. Simple check for chain wear 9.33 Chain line: The highest efficiency and least wear is achieved with minimal lateral deflection of the chain. Chain Maintenance Cleaning, lubrication and replacement are the jobs occasionally required on the chain. Replace the chain if it is (seemingly) stretched so far that it can be lifted off the chainring as shown in Fig. 9.32. Alternatively, you can remove it and measure a 100-link section hanging down: it is worn too far if it measures more than 51”, representing a 2% increase in length. Actually, what seems to be stretch is nothing but the wear of the pins arid bushings, which can be minimized with regular cleaning and lubrication. A well maintained chain can last 5000km (3000 miles) in road cycling, or about half as long in off-road use, and even less if used off-road under unfavorable weather and terrain conditions. Chain Lubrication There are handy aids available to clean the chain with out taking it off the bike. Here the chain is run through a bath of solvent between rotating brushes. Alternatively, remove the chain from the bike and rinse it in a bath of solvent containing about 10% mineral oil to prevent rust, then let it drip out briefly and wipe thy, followed by lubrication. There are effective chain lubricants on the market that do not attract as much dirt as the old-fashioned types. The ultimate in lubrication, hardly known in the US, used to be Castrol chain grease. This is a waxy grease containing graphite particles, which is melted in a pan of hot water, after which the chain is dipped in. The chain is left to soak in the hot lubricant and then removed to drip and wiped clean on the outside. Modern chain lubes are also typically wax-based lubricants, sometimes containing molybdenum disulphide (like graphite, this material works well on the kind of bearings represented by the chain’s pins and bushings). They come in spray-cans, and therefore tempt the user to forget cleaning the chain first. Don’t make that mistake: only use lubrication on a chain that has previously been cleaned thoroughly. 9.34. Chain routing at rear derailleur Replacing the Chain If it should be a chain for a utility bike with a master link, simply remove it by prizing open the spring link with a screwdriver — later reinstall it per Fig. 9.36. Many non-US utility bikes on which this kind of chain is used have an enclosed chain guard, which will have to be opened or removed first to allow this work (which will rarely be necessary, since this guard protects the chain against dirt and rust). 9.36. Installation of connecting link on bike without derailleur 9.35. Use of chain tool to withdraw or in stall link pin; rotation direction 9.37. Using the chain tool to spread, or free a tight link. The narrow derailleur chain is separated with the aid of a chain extractor tool. When reinstalling, keep in mind that chains wear asymmetrically, so when the old chain is installed, make sure it is the opposite way round to stretch its life considerably — the instructions are set up to achieve this. Removal procedure: 1. Place the chain on the smallest chainring and a small sprocket by means of the derailleurs. 2. Install the chain extractor tool on the chain as illustrated in Fig. 9.35 from the outside (RH side of the bike when it is standing upright) on one of the pins between two links, turning it in just far enough to be clamped in place firmly. 3. Screw the punch of the tool in by 6 turns (or 7.5 turns on a V8 wide chain). This will push the pin out of the chain, but not so far that it will drop out the other end. 4. Retract the punch by screwing it back. Twist the chain links on either side apart — if it does not come apart, reinstall the tool and push the pin a little further if necessary, then try again. Installation procedure: 1. Set the derailleurs in such a way that the chain runs over the smallest chainring and the smallest sprocket. 2. Place the chain over chainring and rear sprocket and through front and rear derailleur cage, refer ring to Fig. 9.34. 3. The chain has the right length if it just does not hang through in this position. If this is a new chain, also check whether it fits over the combination large chainring and large sprocket. Then re turn to the original combination with smallest chainring and sprocket. 4. Bring the two chain ends together with the projecting pin on the RH side of the bike. Hold the chain ends in position with the free link at one end hooked on the slight protrusion of the pin on the other. 5. Place the chain extractor tool on the pin and push the pin in by turning the lever while holding the chain together to assure proper alignment. Tighten until the pin projects just as much as the other pins. 6. Flex the chain sideways at the connected point to free the connection enough to assure smooth running of the chain. If it does not work, place the chain link joint on the chain tool in the position marked ‘spreader position’ in the illustration and screw in the handle just enough to free the links, referring to Fig. 9.37. Chain “Jumps” This sometimes happens on a derailleur bike and can have one of several different causes. Certainly if the chain was recently replaced, chances are it is merely due to a stiff link. To check whether this is the cause, set the derailleur to engage the smallest sprocket in the rear, then turn the cranks back slowly, while watching what happens as the chain runs over the rear sprocket. In one position, the chain will lift off the sprocket — check this link for stiffness, loosening it per point 6 of the preceding description. If the problem cannot be eliminated this way, it is usually due to the use of a new chain on an old sprocket, and virtually always happens only on the smallest sprocket, which tends to wear down faster than the others. Since the chain pitch (distance between link pins) does not correspond to the worn and therefore changed pitch of the sprocket, it will ride up and give a jerking action. The only solution is to replace the sprocket, following the description in section 10. 9.38. Pedal cross section The Pedals The pedals, which are shown in cross section in Fig. 9.38, are installed at the ends of the cranks. Fig. 9.40 shows several standard versions. In recent years the so-called clipless pedals have become quite popular. Actually, these are far from clipless: they integrate their own patent clipping device instead of the conventional separate toeclip hitherto used on racing bikes. Whereas the latter can still be ridden with any kind of shoes, the clipless pedals cannot, confining you to the particular type of matching shoes. 9.39. Lightweight platform pedals from the Italian manufacturer Gipiemme. Conventional toeclips are either regular types with straps or open strapless types, which lend themselves well to city riding. The ones with straps are available in several sizes: small, for shoe sizes up to 7 (European size 40), medium up to shoe size 8 1, (European size 43), and large for anything bigger than that. When in stalling the strap through the pedal housing, twist it one full turn between the pedal’s side plates so it does not slip. Supposedly adjustable toeclips with matching pedals are not better than old fashioned clips of the right size, since the former do not place the toe strap in the right position for smaller feet. There are different thread standards for the pedal-to- crank connection, summarized in Table 4. Whether English or French, the LH pedal al ways has LH thread and the RH pedal normal RH thread, whereas non-conforming thread sizes, introduced by Shimano during its brief flirtation with aero dynamic pretense in the early eighties, have disappeared as fast as they were introduced (meaning both pedals and cranks may have to be replaced if you still run into one of these on an older bike). An important dimension for pedals, certainly if in- tended for fast riding, is the one that determines under what angle the bike can lean when cornering without scraping the pedal on the ground. Since this also depends on the bottom bracket height and the spindle length, comparative values are not very reliable except when comparing models by the same manufacturer. By and large, low and narrow pedals clear the road in a sharper corner better than high and wide models, which is important at high speeds. 9.40. Different pedal types: Track pedal, Platform pedal, BMX (or early mountain bike) pedal 9.41. MKS Samson clipless pedal. This is probably the lightest full clipless pedal on the market. Pedal Maintenance Here we shall cover pedal replacement as well as adjustment and overhauling of the bearings. Maintenance is often hampered by the fact that spare parts are not available. While a fall can lead to a bent axle — which is basically a cheap and simple repair, only Campagnolo makes it possible with their admirable policy of spare part availability. The pedals may have to be removed when the bike is transported, and the thread may get damaged if it is not done carefully. Here’s how to do it right. 9.42. Threading for L and RH pedals Replacing Pedal Bracket By way of tools, you will either need a special pedal wrench, any thin, fitting open-ended wrench (usually 15mm), or — if the pedal stub visible from the back of the crank has a hexagonal recess — a matching alien key. In addition, use a rag and some Vaseline. Procedure: 1. To remove the pedal, hold the crank firmly arid un screw the RH pedal by turning the tool to the left (as seen from the pedal), the LH one to the right. 2. To install, first thoroughly clean the screw thread stubs and holes, then lubricate lightly with Vaseline to prevent seizing and ease subsequent removal. 3. If you often remove the pedals, install a flat steel washer between the crank and the pedal to protect the soft aluminum of the crank and ease sub sequent removal. 4. Install the RH pedal by turning to the right (seen from the pedal end), the LH one by turning to the left. 9.43. Pedal removal and installation Adjusting Pedal Bearings The pedal bearings must be adjusted if there is play or they turn poorly. If adjusting does not solve the problem, proceed to the overhauling procedure that follows. This description applies to regular pedals on which the outer bearing is accessible from the end of the pedal, shown in Fig. 9.45. Many newer platform and clipless pedals are not accessible from that end — instead, unscrew the bearing from the body at the stub end. For regular pedals, you will need a pair of pliers or special wrench to remove the dustcap, a wrench to fit the outer bearing locknut, and something to adjust the cone (usually a small screwdriver does the trick). Procedure: 1. Remove the dustcap. 2. Loosen the locknut on the outer bearing by un screwing it by one or two turns. 3. Lift the lock washer clear from the cone. 4. Adjust the cone — turn to the left to loosen the bearing, to the right to tighten it. 5. Put the lock washer back down on the cone and tighten the locknut, making sure the cone and the lock washer do not turn with it (if they do, the lock washer’s key is worn and it must probably be re placed). 6. Check and repeat if necessary (or overhaul if correct adjustment can not be achieved). 7. Install the dustcap. 9.44. Shimano’s elegant clipless pedals are based on the Look patent. Overhauling Pedal Again, this procedure applies to regular pedals see the note in the introduction to the section Adjust Pedal Bearings for pedals without externally accessible outer bearings. You will need a dustcap wrench, a wrench for the locknut, something to turn the cone, bearing grease and a rag. Disassembly procedure: 1. Remove the dustcap. 2. Loosen and remove the locknut on the outer bearing by unscrewing it. 3. Lift the lock washer clear from the cone and re move it. 4. Unscrew and remove the cone, catching the bearing balls. 5. Pull the pedal housing off the axle and catch the bearing balls on the other side. Overhauling procedure: 1. Clean and inspect all bearing parts and make sure the axle is not bent. 2. Replace any damaged or bent parts where available — if not, replace the entire pedal. 3. Fill the bearing cups with bearing grease, then place the bearing balls inside, leaving just a little space between them. 4. Place the housing back over the axle with the end without thread for the dust cap first, taking care not to push the bearing balls out. 5. Alter assuring the outer bearing balls are in place, Install the cone on the spindle. 6. Adjust the cone: turn to the left to loosen the bearing, to the right to tighten it. 7. Put the lock washer on the cone and tighten the locknut, making sure the cone and the lock washer do not turn with it (replace the lock washer if they do). 8. Check and repeat, if necessary (or replace the pedal if correct adjustment cannot be achieved). 9. Install the dustcap. 9.45. Pedal bearing detail Freewheel with Sprockets Except on track racing bikes, all regular bicycles have a freewheel mechanism on the rear wheel hub to allow the wheel to turn forward while holding the cranks still. On utility bikes, the freewheel is often an integral part of the hub (together with brake and gear mechanisms). On derailleur bikes, it is either a standard assembly that is screwed on to the RH side of the hub, or it is a unit that, though strictly separate, remains part of the hub, as is the case on so-called cassette hubs. To ease shifting, specially designed teeth sequences are incorporated In some designs, such as Shimano’s Hyper glide, providing two locations around the circumference where the teeth are so small that the chain is eased over sideways very easily. Fig. 9.49 shows a typical assembly of a screwed-on freewheel block with its range of sprockets. Although rarely seen in the US, there are also similar freewheels with only a single sprockets for one-speed bikes, such as those often used in countries like France, Belgium and Italy. Whatever number of sprockets, and whether built-in or screwed on, the principle of these freewheel mechanisms is always as depicted in Fig. 9.51. Turning the internal body relative to the fixed outer part in one direction engages the pawls, causing the two to turn together. Turning it in the opposite direction, the pawls ride over the teeth against their spring tension, resulting in the familiar freewheeling sound. Only on some bikes with a coaster brake, is a different type of free- wheel used, which will be described in Section 13. When selecting the freewheel block with its sprockets, the major criterion is the number of teeth of the latter. Not all combinations are available for all freewheels, and not every combination makes equal sense for all purposes. This subject will be extensively covered in Section 10, which is devoted to derailleur gearing. The other considerations mainly concern the kind of screw thread: here too, there are different standards, even for normal screwed-on freewheel blocks. Most bikes sold in the US and Britain have rear hubs with Italian standard thread, while others have French standard threading, which do not fit one another with out doing serious damage. See Table 4. Whether to use a 5-, 6-, 7- or even 8-speed freewheel block, largely depends on the hub dimensions. If the over-locknut size of the rear hub is 120mm, only 5- speed versions fit. On 124 to 126mm hubs, all 6-speed and narrow 7-speed blocks fit. Standard width 7- speeds and all 8-speeds require widths of 128mm or more. Of course, the frame’s rear triangle width (measured between the drop-outs) also has to match these dimensions. Most cassette hubs are designed for matching 7-speed units, the freewheel mechanism itself being a (removable) part of the hub, while the sprockets and the spacers are installed on splines with the last one or two screwed on. The two parts of a cassette hub can be separated with a special tool (although it is rarely done), while the conventional freewheel block is un screwed with a crank extractor, as will be described below. 9.46. Highly compact Hugi cassette hub with 8 sprockets and matching narrow Rohloff chain. 9.47. Calorie counter pedals This gadget has strain gauges arid an indicator that registers how much energy is given off over time. 9.48. Look clipless pedal. Maintenance of Freewheel with Sprockets The maintenance operations described here are limited to replacement and lubrication. Usually, what is needed is the replacement of either the entire freewheel block or of an individual sprocket. If there is too much play in the freewheel, evidenced by wobble, it is possible to adjust the bearing play. Finally, we shall cover the replacement of the sprocket on a bike without derailleur. Replacing Freewheel Block This work is often necessary merely to replace a broken spoke on the RH side of the rear wheel, which is generally inaccessible without removing the freewheel block. The other reasons for replacement are when the mechanism or the individual sprockets are worn, or the sprockets are of the wrong size for the required gearing. If this is a screwed-on freewheel, the freewheel extractor for the make and model in question will be needed, in addition to a large wrench or a metal-working vice mounted on a workbench. In addition, use a rag and some Vaseline. Refer to Fig. 9.52 once the wheel has been taken off the bike. Removal procedure: 1. Remove the hub quick-release or the axle nut on the RH side. 2. Place the freewheel tool as far as possible on the splines or recesses of the freewheel body. 3. Install the quick-release or the axle nut over the freewheel tool, leaving about 2mm clearance. 4. Either hold the freewheel tool face down in the vice, or hold it face up with the large wrench. 5. Turn the tool to the left relative to the wheel or, in case it is held in the vice, turn the wheel relative to the tool. You may have to give a firm jolting twist to loosen the freewheel body from the hub’s screw thread. 6. Alter one revolution, loosen the axle nut or the quick-release one turn and continue until the freewheel can be removed by hand. Installation procedure: 1. Clean and lightly lubricate the thread on the hub and in the freewheel. 2. Very carefully align the screw thread on the free- wheel with that on the hub and screw it on by hand — don’t force it, but remove and start again if any resistance is noted. 3. Once it is crewed on as far as it will go by hand, install the wheel in the bike, allowing the normal pedaling force to tighten it further once you start riding. 4. On index gear bicycles, the gearing may not match at first. Just ride the bike about a mile to make sure the freewheel is on as far as it will go before at tempting to readjust the gears. 9.49. Freewheel block with six sprockets: 9.50. Construction of typical freewheel: Detail: cone, drive head. Replacing Individual Sprockets In addition to a rag, you’ll need a sprocket remover, or cog wrench. Quite a few different versions are avail able, but all achieve the same: they allow you to turn one sprocket relative to the one underneath. The wheel must first have been removed from the bike. Refer to Fig. 9.53. Removal procedure: 1. While holding the sprocket underneath steady with one part of the tool, turn the one above it to the left relative to it to unscrew it. On some models, there is a screw-threaded ring on top holding the whole assembly together — it too can be unscrewed relative to the underlying sprocket. 2. Depending on whether the other sprockets are screwed on or held in splines, remove them as appropriate until you have reached the one to re place, keeping track of the sequence of spacers. Installation procedure: 1. Clean and lightly lubricate the various parts and then start assembling them in the appropriate sequence, not forgetting the spacers. Specially shaped sprockets, such as those on the Shimano Hyperglide freewheel, must be installed in the same orientation as the originals. 2. Screw the screwed-on sprockets on with the help of the tool, making sure you tighten them firmly. 9.51. Operating principle of typical free- wheel mechanism. Driving, Freewheeling. 9.52. Freewheel removal Lubrication of Freewheel Mechanism This operation is not usually necessary, but it may be a solution if the freewheel does not turn properly. Some models have a special lubrication hole through which thick oil or light grease can be squeezed. On other models, first remove the wheel from the bike. Place the wheel with the freewheel facing up on a receptacle and start pouring in thick mineral oil while turning the freewheel as shown in Fig. 9.54. Continue until it comes out clean on the other side and the freewheel turns freely. Let drip and wipe with a rag. Adjusting Freewheel Bearing A wobbly freewheel can usually be adjusted by removing a shim under the bearing cone on the outside. To do this, remove the wheel from the bike and place it flat down, freewheel side up. Although some freewheels are constructed differently, you will generally find a pair of recesses in one end of the freewheel, with which you can screw the cone out of the body. This is done with a pin wrench or e.g. with a pointed object and a hammer. If the cone is accessible from the outside, it has to be turned off to the right, installed by turning to the left (LH thread). Be very careful not to lose the bearing balls under the cone when disassembling. Remove the cone and take one of the shims underneath it out, again without losing the bearing balls. Reassemble the cone on the body, and check whether the freewheel runs better. If this did not do the trick, you may have to replace the whole freewheel block. Replacing Single Freewheel Sprocket To do this, the wheel has to be removed from the bike first. If it is a separate screwed-on freewheel (similar to that used on a derailleur bike), follow the same procedure as described above. On hubs with an integral free- wheel mechanism, remove the spring clip that holds the sprocket on the hub. Remove the sprocket, clean all parts and reassemble, clamping the spring clip back into place. Replacing Fixed Sprocket This operation applies to a wheel without a freewheel, such as used on a track bike (also used to advantage on a road bike for training purposes). Fig. 9.55 shows the way this kind of sprocket is installed on the special hub. The hub has two different types of screw thread: a LH threaded section for the lockring and a RH threaded one for the sprocket. You will need a cog wrench, a rag and Vaseline. Removal procedure: 1. Hold the sprocket with the cog wrench and turn the lock ring off to the right (LH thread). 2. Unscrew the sprocket to the left, while countering at the wheel. Installation procedure: 1. Clean and lightly lubricate all parts. 2. Thread the sprocket on firmly to the right. 3. Countering at the wheel (rather than at the sprocket), screw the lock ring into place, turning it firmly to the left. 9.53. Sprocket removal 9.54. Freewheel lubrication 9.55. Fixed sprocket installation: screwed-on sprocket; RH thread; LH thread; (LH thread), (RH thread) Guide to Bicycle Technology (article index) |
| Top of Page | Prev: The Bicycle Wheel | Next: | HOME |