Wartung von Naben
Um aus Naben die löngste Lebensdauer und den geringsten Reibungswiderstand herauszuholen, müssen diese regelmäßig auseinandergebaut, gereinigt, wiedereingepackt (Fett) und neu eingestellt werden.
Werkzeuge und Materialien
If possible, you should have two special cone wrenches for each size needed to fit your hubs. This usually means two sets of cone wrenches. A set usually includes four sizes: 13, 14, 15 and 16 millimeter, and few cones are not covered by such a set. (Among the exceptions is Dura-Ace, which requires 17 mm wrenches). You can get by in most cases with one cone wrench of each size and an open-end wrench or adjustable wrench for the locknuts, but it is much easier to do the final adjustment if you have two of each needed size. These wrenches are available only in bicycle shops. See the companion article on cone wrenches for advice on selection and use.
To clean the parts, you should have an old toothbrush, a supply of clean rags or paper towels and a good degreasing solvent. The degreaser is available in hardware and automotive stores. Follow the directions on the degreaser for use. The best type of degreaser uses a water rinse after the grease has been dissolved by the solvent. If you don't have the degreaser you can make do with WD-40, LPS-l, paint thinner or kerosene, but you will have to do a lot of scrubbing if your hub has caked-on dried-up grease. Do not use gasoline. It is a serious safety hazard: its vapor can crawl along the floor and be ignited by any spark or pilot light. Any of the stronger solvents can smell up an entire house, so they are best used outdoors or in a detached shed or garage. Non-toxic solvents such as Citrasolv are also available, are effective, and are less troublesome.
You also will need a small amount of grease. The best grease that I know of for this purpose is Phil Wood bicycle grease (available at well-stocked bicycle shops). This is a fairly thick grease, which makes for easier assembly because it holds the bearing balls in place while you are installing the axle and cones. This grease also is very long-lasting and water-resistant. Some people prefer a lighter grease, such as Campagnolo or Lubriplate #105. These offer slightly less friction, though they seem to be not as long-lasting. Automotive wheel-bearing grease also is suitable. Boat-trailer wheel grease is a good choice for a bicycle used in wet conditions.
The difference between oil and grease is mostly a difference of degree. Grease is very thick oil; oil is very thin grease.
Some racers use oil instead of grease, for less friction. If you use oil, you must oil the hubs every week or two, or risk serious damage to them. This is generally not worth the trouble! The difference is easily felt when spinning the hub axle with the fingers but is insignificant when the hub in use. For one thing, the bearings are moving slowly, at the center of the wheel. The friction due to the load is in any case many times greater than that due to the viscosity of the lubricant. The friction in any good hub is minuscule compared with the rolling resistance of the tires. Grease may even result in less friction, by providing a more robust lubricating film.
Have a new set of bearing balls on hand. They are sold at bicycle shops and over the Internet. Get a couple of spares in case you lose some -- they can be elusive little devils. It is hardly worth the trouble to rebuild a hub without new bearing balls. Most front hubs take 10 three-sixteenth-inch balls per side. (Exception: Campagnolo Record, Nuovo Record and Super Record take 7/32 inch balls.) Almost all rear hubs take nine 1/4 inch balls per side.
Demontage
I would suggest that you start with the front wheel if you have not done this job before, because there are fewer complications. Before you remove the axle, check to see if it is bent. Remove the axle nuts or quick-release skewer that holds the wheel to the fork. Now if you rotate the axle and look at each end of it in turn you should be able to tell if the axle is bent. If it is, one end or both will wobble back and forth as it is turned.
Newer Shimano hubs have rubber dustcaps which you must pop off before you can do any further disassembly. Otherwise, your first step is to loosen one locknut.
If one locknut breaks free, fine -- some hubs use a keyed washer between each cone and locknut. The washer has a "key" or tab which slides in a groove cut in the threads of the axle. This washer will keep the cone from turning with the locknut. With such a hub, you might put a wrench on the locknut at each end of the axle and unscrew one from the other. Many newer hubs leave out the keyed washer, and so, use a cone wrench on the cone, and another wrench on the locknut on the same end of the hub. Otherwise, they are likely to turn together and be hard to turn. Also see special instructions for Raleigh front hubs.
There is an additional complication when you are working on a freewheel rear hub, because the freewheel block gets in the way. If you have the necessary tools (a freewheel puller to fit your brand of freewheel and a sturdy vise mounted on a solid workbench, or large -- additional advice is in the article on freewheels), the easiest approach is to remove the freewheel first. If this is not possible, you can do the job without removing the freewheel. Remove the locknut and cone on the left side of the hub and pull the axle out from the right side. You will just be able to get at the right bearing cup through the center of the freewheel.
On a cassette Freehub, the right-side bearing is more accessible, but it is easier to clean out the right-side bearing if you remove the lockring first. Instructions are in my article on cassettes.
It will not be nearly as easy to clean the right cup with the freewheel or cassette lockring in your way, but fortunately that side rarely gets dirty, because these parts make it harder for dirt to get in. Be careful not to get solvent inside of the freewheel or Freehub mechanism While you have the axle out of the hub, tighten the spacer for the right end of the axle tightly against the locknut and cone so you will be able to use a wrench on the locknut to hold the axle when you are adjusting the cone on the left. If you have put a new axle on a rear quick-release hub, it likely will be too long for the quick release to work properly. If so, it is easiest to cut it down after it is installed in the hub.
Lift off the washer, if present, and unscrew the cone. Once the cone has been removed from one end of the axle, the axle can be pulled out of `the hub, and the ball bearings will fall out. There is no need to remove the other cone and locknut that are still on the axle, so save yourself a lot of trouble and leave them on the axle, unless your old axle is bent and has to be replaced anyway. Remove the dustcaps by carefully prying them up with a screwdriver. If you have trouble getting the dustcaps off, leave them on rather than bending them. This will make it a bit harder to clean out the hub.
Reinigung
The most important part of this job is getting all the internal parts as clean as is humanly possible. The inside of the hub shell, the axle, cones and balls must be completely free from old grease, dirt, dust and solvent. If you don't remove all traces of solvent, it will attack the new grease you will install later and the whole procedure will have to be done over again far too soon.
You may go so far as to push a wad of Kleenex through the hub barrel, and to clean out recesses with a Q-tip. If the hub has an oil clip, remove it, clean it and clean the oil hole. If you are not using a degreaser that follows up with a water wash, you could instead wash the parts with dishwashing detergent, rinse them and heat them gently so they dry before rust begins to form.
When you are done with the toothbrush, clean it very carefully before using it again to brush your teeth.
[Sheldon actually used that line when he taught bicycle repair at the Boston Center for Adult Education in the 1970s. It may have been a bit much for publication in Bike World, but in the true spirit of Sheldon, I have repeated it here -- John Allen]
Now that the parts are clean, they should be carefully examined for wear. The cones should have a shiny track running around them where the balls roll against them. Examine this track very carefully to see if there are any irregularities or pits. A magnifying glass may be of help here. If there is any sign of a flaw, no matter how small, a cone should be replaced.
Examine the cups (in the hub shell) in the same way. In most cases it is not possible to replace the cups without replacing the whole hub, but fortunately the cups usually are the last parts to wear out. If the hub is cleaned regularly, lubricated and kept in good adjustment, the cups should last indefinitely.
One of the reasons why I suggest routinely replacing the balls is that it is very easy to fall to see pitting or crud on a ball, since you can't be sure that you have seen every side of it. When I am repacking a hub, if I drop one of the new balls on the floor, I don't even bother to pick it up. I use another new one rather than contaminate the bearing by putting in a possibly dirty one.
It is particularly important that all of the balls in a given race come from the same production run. They are made to tolerances of 3 or 4 millionths of an inch. One batch may be oversize, while the next batch may be several millionths undersize. If some of the balls in a race are that much smaller than others, the smaller ones might just as well not be there, because only the larger ones will be taking the load.
The balls need to fit easily into the race. If there is one too many, the wheel will tilt slightly one way and another after installation, and can not be trued.
Zusammenbau
If you removed the dustcaps, the first step in reassembly is to put them back in, unless they are the rubber dustcaps. Gently tap them into the hub shell with a hammer, working your way around the outer edge of the cap. Then line both cups in the hub shell with grease. Don't worry about using too much. It is not possible. If in doubt, use more.
Next, lay the wheel on its side, and insert the end of the axle that does not have a cone on it part way into the hub from above. (If you are doing a rear hub, make sure that the axle is going in the same way it came out, so that the long end will be on the freewheel side.) With the axle blocking the hole in the barrel of the hub, you can install the balls in the upper cup without any risk of having them fall through.
Now, lift up the wheel and let the axle drop down so that the cone rests on the balls that have just been installed in the cup. Hold onto the axle and turn over the wheel. Don't let go of the axle until it is resting on your work surface, or the balls may fall out. Install the balls in the other cup and screw the remaining cone onto the axle hand tight. This will secure the assembly so that you can now handle it without risk of dropping bearing balls on the floor. Install the lockwasher and locknut, and you are ready to adjust the bearing.
Adjusting ball bearings of the type used on bicycles is not difficult, but if you haven't done it before it is likely to take some time and patience. Don't be in a hurry.
What is meant by "adjustment of bearings" in the case of hubs is basically how far apart the cones are from one another on the axle. If they are too close together, they will pinch and bind against the balls, and the axle will be difficult to turn. The bearing will have too much friction and the parts will wear out prematurely. If the cones are too far apart, everything may roll freely enough, but there will be looseness or play in the bearing, and your wheel will wobble from side to side like loose tooth. The ideal is to find the point where the cones are loose enough that the axle turns as freely as it does when the cones are too loose, but with as little play as possible.
It is meaningless to try to judge the cone adjustment when the locknuts are not tight, because when you tighten the locknut, it changes the cone adjustment. What you have to do is to try different adjustments, checking each time for two things--friction and play.
To check for friction, pretend you are a safecracker and the axle is the knob of a safe. Turn it slowly and smoothly, several revolutions in each direction. It should move with the gentlest pressure, without any unevenness or binding. If you are not sure whether it is binding or not, try loosening one of the cones a bit. If it turns any easier, the previous adjustment was too tight.
To check for play, see if you can get the end of the axle to wiggle up and down or side to side. If there is play, you should be able to feel it with your fingers. There is a more detailed article about cone adjustment on this site. It descdribes some useful tricks to fine-tune the adjustment
It should be possible to adjust a good-quality hub so that there is no perceptible play, with no more friction than is present when the cones are too loose. If you are unable to get the hub to pass both tests with the same cone adjustment, take it apart again and repeat the whole procedure. Your problem is either attributable to dirt in the races (even a single dust particle can cause trouble), pitting on the bearing surfaces, a bent axle, or a basically poor-quality hub (such as the pressed-steel hubs that come on cheap bicycles). Also check whether you might have installed one too many bearing balls. If nothing you can do will eliminate both the binding and the play at the same time, it is better to adjust a little loose and accept a slight amount of play then to have the hub bind.
No binding with no play is the proper adjustment for solid-axle hubs, but if you have quick-release hubs, there is an additional, complicating factor. When you tighten the quick-release lever, it tends to compress the axle just a little bit. If the adjustment was just right with the wheel on your bench, it will be too tight when the wheel is installed and the quick release tightened. For this reason, quick-release hubs should be adjusted so that there is a very sight amount of play in the axle when the wheel is not installed. This play should disappear when the quick release is tightened to the dropouts. My article on cone adjustment describes a special home-made tool lets you get the adjustment right when the wheel is off the bicycle. You might also keep a pair of dropouts sawn off a junk fork, so you can tighten the quick release on them and still spin the axle to check for binding.
Bearing adjustment also can be checked by lifting the bicycle off the ground and trying to wiggle the rim back and forth between the brake shoes. There should be no rattling sensation. Now keep the bike off the ground and let go of the wheel. The weight of the valve should be sufficient to cause the wheel to swing back and forth several times before the wheel comes to a stop with the valve (or whatever part of the rim-tire-tube combination is heaviest) at the bottom. This test will not work on the rear wheel unless the chain is disengaged from the rear sprockets.
The hubs should be repacked at regular intervals as part of the normal maintenance of your bicycle. How often it is necessary will depend on how much you use your bike and under what conditions. If you only ride on sunny days and have good luck, you might be ,able to go a couple of years, but if you ride in the rain, or if you live in a sandy or dusty area, you may have to repack your hubs every couple of months. The interval can be extended considerably by installing external seals to block the entry of dirt. (See Sealing Your Bike Components for Under $ 10 by John Allen, July 1977 Bike World.) [But also see Jobst Brandt's comments on sealed bearings, on this site. -- John Allen]
Rather than repacking your hubs on a fixed schedule, I recommend that you periodically check the condition of your hubs by removing the wheels and feeling how freely you can turn the axles (in the same manner described previously). Do not be fooled because your hub may seem to have "just a little" friction. Frictional drag depends on the load on the bearing. When you are holding the wheel and turning the axle by hand, the only load is the weight of the axle set and the viscosity of the lubricant. When you are riding your bike, the load is the weight of you and your machine, and the frictional drag is increased by many times. You can feel the difference.
Siehe auch
Quelle
Dieser Artikel basiert auf dem Artikel Tool Tips Hub Overhaul von der Website Sheldon Browns. Originalautor des Artikels ist Sheldon Brown.
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