Wartung von Steuersätzen
Der Steuersatz ist eine Kugellagerbaugruppe, die dafür sorgt, dass die Gabel und der Rahmen miteinander verbunden werden. Er erlaubt es, dass sich die Gabel frei drehen kann, so dass man Lenken und die Balance halten kann.
Der Steuersatz besteht aus vier Lagerschalen und weiteren zugehörigen Teilen - von Oben nach Unten:
- Die einstellbare Lagerschale verbindet sich mit dem Gabelschaft
- Die obere Kopflagerschale wird von oben in das Steuerrohr eingepresst.
- Die untere Kopflagerschale wird von unten in das Steerrohr eingepresst.
- Der Gabelkonus, der am unteren Ende des Gabelschafts unmittelbar oberhalb der Gabelkrone sitzt.
Es gibt zwei gebräuchliche Steuersatzarten: Gewindesteuerstz und Gewindeloser Steuersatz.
| Gewindesteuersatz | Gewindeloser Steuersatz |
|---|---|
| Man beachte die Mantelflächen an Mutter und der oberen einstellbaren Lagerschale |
Man beachte die Klemmschrauben am Vorbau. Es gibt keine Mantelflächen für Schlüssel |
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- Klassische Gewindestauersätze passen auf Gabeln, deren Gabelschaft ein Gewinde tragen. Die obere Lagerschale wird auf den Gabelschaft geschraubt und die Mutter wird danach oben auf geschraubt, um das ganze zusätzlich zu sicherrn. Zwischen Lagerschale und Mutter sitzt normalerweise noch eine Sicherungsscheibe, die die Konstruktion gegen ungewolltes Aufschrauben sichert.
Zusätzlich zur Sicherungsscheibe können noch ein oder mehrere Spacer als Abstandshalter eingesetzt sein. - Gewindelose Steuersätze, die bei den meisten neuen Fahrrädern (seit den 1990er Jahren) eingesetzt werden, passen auf Gabelschäfte ohne Gewinde und benutzen eine Klemmung oder eine Manschette zum Sichern der oberen Lagerschale. Normalerweise übernimmt der Vorbau die Funktion beider Vorrichtungen.
Bei den meisten Fahrrädern ist es egal, welchen Steuersatztyp man einsetzt, solange er die richtige Größe hat. Bei einem beliebigen Rahmen kann man Hin- und Herwechseln zwischen Gewinde- und Gewindelosem Steuersatz, in dem man folgende Komponenten tauscht:
- Die Gabel
- Den Steuersatz
- Den Vorbau
Größen
Die nominale Größe eines Steuersatzes basiert auf dem Außendurchmesser des Gabelschafts. Daher kommt es zu einigem Durcheinander, da ausgerechnet das größenangebende Bauteil normalerweise am komplett aufgebauetn Fahrrad nicht sichtbar ist. Der Gabelschaft verschwindet im Steuerrohr des Rahmens.
Größenbestimmung beim Gewindesteuersatz
Bei einem Fahrrad mit klassischem Vorbauschaft und Klemm- oder Spreizkeil ist der Vorbauschaft 1/8 Zoll (3,2 mm) kleiner als der Gabelschaft. Manche Leute mesen den Durchmesser des Vorbauschafts und meinen dann fälschlicherweise, das sei die nominelle Größe ihres Steuersatzs
Die allermeisten Gewindesteuersätze haben die Größe 1 Zoll (25,4 mm). Eine Minderheit hat die Größe 1 1/8 Zoll (28,6 mm). Es gibt weitere Größen, die aber extrem selten sind. Die Illustration unten zeigt, wie man einen 1 Zoll (25,4 mm) von einem 1 1/8 Zoll (28,6 mm) Steuersatz unterscheidet:
| 1 Zoll (25,4 mm) Gewindesteuersatz | 1 1/8 Zoll (28,6 mm) Gewindesteuersatz |
|---|---|
| Der 7/8 Zoll (22,2 mm) Vorbauschaft ist merklich kleiner als eine 1/4 Dollar Münze | Der 1 Zoll (25,4 mm) Vorbauschaft ist ein klein wenig größer als eine 1/4 Dollar Münze |
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Es geht aber noch einfacher: Man nehme eine gebräuchliche 20 (Euro-)Cent Münze. Diese ist (fast) exakt so groß wie ein 7/8 Zoll Vorbauschaft (Münze 22,25 mm, Vorbauschaft 22,2 mm). Ist also der Vorbauschaft genauso breit wie die 20 Cent Münze, handelt es sich um einen 1 Zoll Steuersatz. Ist der Schaft merklich größer - rund 3mm mehr sind deutlich sichtbar - als die 20 Cent Münze, dann handelt es sich um einen 1 1/8 Zoll Steuersatz
Weitere Maße
Es gibt noch weitere Maße, die wichtig sind, wenn man den Steuersatz tauschen möchte:
- Der Außendurchmesser der Steuersatzschale (obere und untere Kopflagerschale), der zum oberen und unteren Innendurchmesser des Steuerrohrs passen muss.
- Innendurchmesser des Gabelkonus, der zum Außendurchmesser des Gabelschafts passen muss.
- Gewindesteigung bei Gewindesteuersätzen
- Bauhöhe des Steuersatzes. Falls der neue Steuersatz weniger hoch baut als der alte, kann man Spacer benutzen, um die alte Bauhöhe wieder zu erreichen. Wenn der neue Steuersatz aber zu hoch baut, können Bauteile über die Oberkante des Gabelschafts hinausragen und einen ordentlichen Zusammenbau verhindern.
- Es gibt weitere Variationen in Tiefe und Form der Fassungen am oberen und unteren Enmde des Steuerrohrs. "Standard", "Integrierter Steuersatz", "Semiintegrierter Steuersatz", "Low Profile Steuersatz". Integrierte und Semiintegrierte Steuersätze benötigen Steuerrohre mit größerem Durchmesser, in die bereits Laufflächen für die Kugellager ausgespart sind.
Wenn Du Dir nicht sicher bis wegen aller dieser Maße, nimm den alten Steuersatz oder den Rahmen sowie die Gabel mit, wenn Du einen neuen Steuersatz einkaufst. Gebräuchliche Maße zu Steuersätzen findest Du auf folgendem Spickzettel:
Probelme und Ihre Behebung
Folgende Symptome können erkannt und behoben werden.
Wackeln
Wenn der Steuersatz wackelt, ist das ein Zeichen dafür, dass er zu locker eingestellt wurde. Das überprüft man am einfachsten, indem man die Vorderradbremse betätigt und den Lenker vor- und zurückbewegt. Wenn man einen merklichen Schlag fühlt (oder schlimmstenfalls hört), heißt das normalerweise, dass der Steuersatz zu lose ist. Dass dies vom Steuersatz und nicht von der Bremse herrührt, kann man leicht feststellen, indem man einen Finger auf den Spalt zwischen die Lagerschalen am oberen oder unteren Ende des Steuerrohrs legt. Wenn sich das Fahrrad bei ausgebautem Vorderrad im Montageständer befindet, kann man auch an den Gabelenden drücken und ziehen.
Schwergängigkeit
Wenn der Steuersatz zu stark vorgespannt ist, wird er schwergängig. Das kann man feststellen, indem man das Fahrrad vorne (nicht am Lenker!) anhebt, so dass das Vorderrad in der Luft ist. Normalerweise wird das Vorderrad sich durch sein Eigengewicht zur einen oder anderen Seite hin bewegen. Im Montageständer bei demontiertem Lenker und Vorderrad spürt man beim bewegen der Gabel einen sanften, gleichmäßigen Zug durch die Kugellagerdichtungen. Das ist völlig normal. Rauheit oder Ungleichmäßigkeiten in der Bewegung deuten auf Probleme hin.
Wackeln und Schwergängigkeit zusammen
Sometimes you will find both of these faults at the same time. This indicates a more serious problem, not just an adjustment issue. You may find that the headset is loose when the fork is facing straight forward, but gets tight when you turn the handlebars to one side or the other, or that it simply can't be adjusted. Possible causes:
The fork steerer may have been bent in a crash. Generally, this is not repairable, and you need to replace the fork. One or more of the bearing races may be installed slightly crooked. This usually is fixable by having the frame's head tube and the fork's crown machined or "faced" to ensure that the races install with correct alignment. This requires expensive special tools that only better bike shops have. One or more of the bearing races may be loose where they attach to the frame/fork -- or a cartridge bearings may not seat tightly against a race. This will cause looseness as the race wiggles back and forth, even though the bearings may have been tightened up sufficiently to eliminate bearing play. The fork crown race most often gives this problem.
If the crown race is loose, sometimes you can fix it by using a hammer and centerpunch to create a series of "craters" in the side of the surface that locates the crown race. The raised edges of the craters may be just enough to remove the slop.
Alternately, you may go to a different size headset. In particular, if you are working with a J.I.S. frame and fork, it can be re-machined to work with an ISO headset. Since J.I.S. head tube races are smaller, and J.I.S. crown races are larger, there is material available to be machined away to upgrade to ISO.
You might also use "plastic steel" (epoxy glue with a filler of steel particles, available at hardware stores) to build up the space between a bearing race and its seat. Be sure to clean off the excess, so steel particles don't get into the bearing. Assemble and adjust the headset before the epoxy sets, so the races will seat fully. You may have installed a bearing retainer upside down. This is not uncommon. There is no real standardization as to which way the retainer faces, so it's easy to err. However, if you take a careful look at the races of your particular headset, you will see that if you install the retainer upside down, the retainer can come into contact with one of the races. Just flip it over. The retainer must not be in contact with anything but the bearing balls. If the headset uses loose bearing balls, there may be too many, so they jam against each other. A bearing ball or balls may have moved out of line during installation, so it is rubbing rather than rolling. The headset may have been assembled from mismatched parts. It's OK to replace only the bottom or top parts of the headset as a unit, but the two bearing races at the top, and the two at the bottom must match, and the bearing balls and retainer (or cartridge) need to be the right size, or else all bets are off.
Einrasten (Stillstandsmarken)
All of the other ball bearings on a bike spend their lives rotating round and round, but headsets spend most of their time pointing straight ahead. Sometimes you will see that the bearing balls have created a neat row of little dents in the bearing surface of the lower frame cup and/or the crown race. This creates the effect commonly known as "indexed steering" where the balls sort of "snap" into place, and the fork tends to stick in the straight-forward position.
brinell led
A "Brinelled" crown race (larger than actual size)
The dents in the races resemble the dents created by the Brinell hardness test procedure, and as a result, this type of damage is sometimes called "Brinelling." This is a bit of a misnomer, because the Brinell hardness test involves basically hammering a bearing ball into a metal sample with one good hard whack. Some folks assume that the dents in headset races also result from impact, but actually that is not commonly the case. Instead, it has to do with lubricant breakdown. Jobst Brandt has an article on this site describing the process in detail.
Ideally, a "Brinelled" headset should be replaced, but you can often cure the problem by replacing the retainer with loose balls. You use the same size balls, but can usually fit more of them into the races if you leave the retainer out. As a result, the greater number of balls, closer together, no longer all line up with the dimples in the races.
A headset race can, on the other hand, become indented due to overload in a crash. The dents then will be deeper in the part of the way around the race that took the impact. Usually, in this case, the fork will be bent too. The indented race(s) and the fork need to be replaced.
Adjustment
The adjustable race is secured by either a:
Star fangled nut and cap, or compression rings in the case of some threadless headsets or a: Keyed washer and lock nut, for threaded headsets.
Adjustment (Threaded)
Adjustment is easiest if you use two wrenches. You may use large end wrenches, or special wrenches made to fit the wrench flats of the locknut and top race -- but in a pinch, you can get by with a single large adjustable wrench. There is some risk of stripping out the tab of the keyed washer or of its damaging the threads of the steerer if you use a single wrench.
Leave the bicycle right-side-up with the front wheel resting on the floor. Loosen the locknut. Preferably, hold the top race from turning with one wrench while turning the locknut with another. If using one wrench and the top race starts to turn along with the locknut more than a tiny bit, go looking for a second wrench. (Skip this step if threads and washer are greased.) Unless the threads and keyed washer are already greased, remove them. Do not unscrew the top race, unless you are going to go to overhaul the headset -- loose bearing balls might fall out. (Skip this step if threads and washer are greased.) Grease the keyed washer and the threads of the steerer. (Skip this step if threads and washer are greased.) Replace the keyed washer, and screw the locknut.down most of the way, leaving it loose.. By hand, without using a wrench, screw down the upper head race until the bearings just begin to bind, then back it off about 1/8 turn. (Tightening the locknut will press down the upper head race, due to its slight looseness on the threads.) Tighten the locknut lightly and test the bearings for free rotation with no excess play. Unless the adjustment is perfect, loosen the locknut and readjust the bearings as necessary. When the adjustment is correct, tighten the locknut fully and check again.
Older French threaded headsets use a serrated or pinned keyed washer which mates with the upper head race. With these headsets, you must back off the locknut farther so that you can rotate the upper head race.
Adjustment (Threadless)
Threadless headsets have an adjustable race that slips over an un-threaded steerer. There are three distinctstarnut types of threadless headsets which adjust differently:
"Aheadset" style threadless headsets, the most common type, require a threaded fastener such as a Star Fangled Nut (photo at right) to be installed inside the steerer.
This type of headset must be used with a special handlebar stem that clamps onto the outside of the steerer, either with one or more binder bolts, or other means. The stem is further secured by a plastic or metal cap which is bolted to the star nut.
To adjust an "Aheadset"-type headset, the stem binder must be loosened, then the bolt that runs through the cap to the star nut is tightened, usually with a 5 mm Allen wrench. This presses the stem down against the tapered bushing that fits inside the adjustable cup. and takes up the slack in the system. The stem is then aligned with the front wheel and tightened with its binder bolts. Once the stem binder bolts have been tightened, the adjusting bolt that goes to the star nut is under no significant stress, and may even be removed. This makes some unusual customizations possible, for example, adding a wedge/expander-type stem to hold a second set of handlebars! "Diatech" headsets from Dia Compe use a special pair of collars, usually mounted just below the stem and above the top race. The lower collar has a beveled, conical top surface, which fits inside of a matching bevel on the inner circumference of the upper collar.
The upper collar has a gap at one point, with a binder bolt to squeeze the gap together. (This upper collar may also include a cable stop for the front brake, if the bicycle has a rigid fork and conventional cantilever or centerpull brakes.)
The handlebar stem is clamped tightly to the steerer, preventing the upper collar from moving upward. As the upper collar is compressed by the binder bolt, it squeezes the lower collar downward, taking up any slack in the headset bearings. The YST "GeForce" headset, unfortunately no longer made, has a collar which slips over the steerer, clamped to it with a binder bolt. The outside of this collar is threaded, and the upper bearing race screws onto these threads. The assembly is fitted with a binder bolt that clamps it tight onto these threads when the desired adjustment has been attained.
The GeForce is the only threadless headset which doesn't use the handlebar stem as part of the adjustment. This headset could be used with any stem, either external clamping or internal expander/wedge type. It is commonly found on Bike Friday folding bicycles made in the mid-1990s.
To adjust a GeForce headset, loosen the binder bolts in the collar and the top race; screw the collar and upper bearing race together, then back off by a fraction of a turn. Tighten the binder bolt of the collar while pressing the assembly down; turn the top race to adjust it; then tighten the binder bolt of the top race. The collar uses a 4 mm Allen wrench, and the top race, a 2.5 mm Allen wrench -- available at some bike shops and at better hardware and auto parts stores. You might take the collar/upper bearing race assembly with you to check the fit of this wrench when you buy it.
Overhaul
Headsets are pretty durable, and hardly ever need to be serviced if your bicycle has a front fender.
If you ride without a front fender in wet conditions, the front tire will spray filthy, gritty water right up into the lower race. (It is the lower race that supports your weight. Most headset failures occur at the lower race.)
To overhaul a headset, you first have to remove the stem. It usually also makes things easier if you remove the front fender, wheel and brake, or at least disconnect the front brake cable.
If you have a cyclecomputer pickup mounted on the fork, you'll also need to remove one end or the other of the computer wiring.
It helps also to turn the bike upside down once the stem has been removed -- easier with a workstand. Don't rest old upward-arched drop-bar brake cables on the floor.
Threaded: Unscrew the lock nut, remove any washers, then unscrew the threaded bearing race. You'll be able to just lift the fork out of the frame. Threadless: Once the stem is off, all of the spacer washers should come off easily. The upper bearing race may be a snug fit to the steerer, so you might need to give the top of the steerer a rap with a mallet to break it free.
Once you have the fork out of the frame, you can see what kind of bearings the headset uses. The illustrations below show the assembly order for typical headsets with different types of bearings. A headset may or may not have contact-type seals as shown under the lower bearing of the headset at the left. This threaded headset has bearing balls in cages (retainers), though generic loose bearing balls can be installed as replacements in most headsets which were supplied originally with retainers. This threadless headset has cartridge bearings. Only exact replacement cartridges will work. Cartridge bearings are mostly to be found in newer, threadless headsets.
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Once you have removed the fork, you can check the condition of cartridge bearings by turning them with your fingers. They should turn smoothly, though there will usually be some drag from bearing seals. Exact replacement is needed with cartridge bearings -- or else, replace the entire headset.
After cleaning a headset that uses retainers or loose bearing balls, check the bearing races for indentations and pitting.
If the headset uses bearing balls held in retainers, you could re-use them if they are still in good condition too. There's little standardization among different makes/models of headsets, so finding a replacement retainer may be difficult or impossible. The top and bottom retainer are usually identical, and exchanging them will increase wear life. It may be possible to pop the old bearing balls out of a retainer and insert new ones, taking care not to bend the retainer. You can increase the load capacity and wear life by replacing retainers (especially the bottom one) with loose bearing balls, though in some cases it's difficult to keep loose balls in place during reassembly.
If the headset had loose bearing balls, replace them...they're cheap enough! You very likely lost some anyway when you disassembled the headset. Most headsets use either the 5/32" or 3/16" size.
For re-assembly, it is very helpful to have the bike mounted upside down in a work stand.
If you lower the steerer partway into the head tube, you will be able to load up the bottom (but facing upward) head tube race with bearing balls without worrying about having them fall down through the head tube, because the steerer will fill the gap. Use enough grease to hold the bearing balls in place. Leave the race one ball short of full, so the balls won't jam up against each other when you reassemble the headset. Once all the bearing balls are in place, add lots more grease, to help seal out dirt when the bicycle is in use.
Once the balls are in place for the lower part of the headset, you can drop the fork down the rest of the way into the headset.
Grease the inside of the upper race, and get it started onto the steerer. Load it up with balls, add more grease, then slide (threadless) or screw (threaded) it "up" to take up most of the slack in the system, so the balls can't fall out.
For a threaded system, you can then turn the bike right-side up to complete assembly/adjustment and wipe off the excess grease.
For a threadless system, you need to secure the fork before turning the bike right-side up. I sometimes use an old toe strap for this, tying the fork crown to the down tube of the frame.
Replacement/Installation
Removing and re-installing the headset bearing races is not necessary for a normal overhaul, only when you are replacing the headset or installing a new fork.
If you are working with an inexpensive all-steel headset, you can often manage with basic hand tools, but if your headset has aluminum or plastic parts, you really need specialized tools made for the purpose. These tools are generally not economical for a home mechanic to purchase, given how rarely they are likely to be used.
The following assumes you're working with an all-steel headset:
Removal:
The races can usually be removed with a hammer and an old flat-blade screwdriver that you don't care about.
The head tube races usually come out pretty easily if you stick the old screwdriver down into the head tube until it hits the internal edge of the race. Tap gently once, then move the screwdriver to the opposite side of the head tube. Keep going back and forth every other blow, so that you won't be driving the race out crooked, which could damage the head tube.
The fork crown race is sometimes more challenging, depending on the construction of the fork crown and the width of the race. You may or may not be able to get a good purchase on the underside of the race.
If the race has a good overhang on both sides of the fork crown, a bench vise is often best for this. Open the vise just wide enough to permit the fork crown to fit through loosely, so that the crown race is sitting on top of the vise jaws. Use a mallet to rap on the top of the steerer, driving the fork down and away from the race. It is a good idea to thread the headset locknut onto the steerer before doing this, to prevent damage to the threads of the steerer.
Alternatively, a bicycle workstand can be used to clamp the steerer with the fork upside down. You can use the hammer and old screwdriver to drive off the race.
Some races and some fork crowns give very little to grab onto. There are special shop tools to work around this problem, so you might want to just bring the fork into your local shop and have it remove the race.
Replacement:
The press-fit races need to be seated firmly.
The head tube races can be tapped into place with a mallet and a block of soft wood that spreads the impact all the way around the margin. Use another block of wood to support the other end of the head tube, and be sure it's sitting level so you don't damage it. Bike shops have threaded tools to pull the races into place.
The fork crown race is more difficult to seat. You can tap on one side and the other, inboard next to the steerer with your old screwdriver, or you may tap on a length of pipe that just fits over the steerer. Turn the pipe around as you tap, in case the surface which rests against the crown race isn't perfectly level.
If you don't get the races firmly seated, they will seat themselves during riding, and the headset will loosen. It then only needs to be readjusted. If working on someone else's bicycle, you should be sure to get the races seated fully before delivering it. If you don't have special tools, you could go for a short, bumpy ride to seat the races, then readjust the headset.
Also see my Adventure Cyclist article about headsets.
Siehe auch
Quelle
Dieser Artikel basiert auf dem Artikel Servicing Bicycle Headsets von der Website Sheldon Browns. Originalautor des Artikels ist Sheldon Brown.