the head tube bearing.
The fork tube rotates in the head tube by means of a cup / cone bearing. see figure 34 . A cup / cone bearing is a bearing that can record forces in all directions, because the running surfaces of the bearings are inclined. This is in contrast to axial or radial bearings. Most of the bearings on a bicycle are then also as a cup / cone bearing performed. Due to the inclined running surfaces the bearing is also easily demountable and adjustable.
A well-functioning head tube bearing is essential for a good steering behavior of the bicycle. The head tube bearing functions well as the cups are straight pressed into the head tube, the surface of the cups and cones is clean, the fork cone well right is pressed onto the fork, the balls are clean, the bearing adjusted well, the bearing is clean and it has sufficient bearing grease.
On a head tube bearing come very large forces, both in the axial and radial direction. It is important, therefore, that the balls and ball tracks are sufficiently hard to absorb these forces. When the load on the fork, is to see that the forces which it exerts on the lower fork are particularly large due to the impact and brake load. An additional disadvantage of the head tube bearing is that it turns very little. The bullets always press the same spot on the cups and cones.
A standard head tube bearing consists of a fixed cone which is pressed onto the front fork, bullets or bullet rings, solid top and bottom cups are pressed into the head tube, a pair of cone which is screwed onto the fork, a lock washer and a nut which turned against the retaining ring is to secure the bearing. See Figure 35 .
In many bearings are balrings used for quick installation. The disadvantage of this is that the number of balls to be placed in the bearing decreases, so that the power per ball is greater.Recommendation is to fill the bearing with loose balls.This is certainly true for the lower bearing because of the greater pressure forces.
In order to absorb the large compressive forces, there are also steering bearings with needle bearings. See Figure 36a and Figure 36b . instead of balls these bearings rollon small cylinders (needles), which creates a line contact rather than a point contact. The roller surface is much larger with needle bearings which can absorb much greater forces. With ball bearings it may happen that, due to the greater forces, there are wells in the cup and cone are beaten by the front fork. Usually it is, therefore, only by this bearing designed as a needle bearing. The needle bearings are not loose in the bearing positioned but are mounted in a special cage.A headset with needle bearings has special cups and cones with a flat rolling surface of the cylinders.
Shimano provides a “cartridge” headset with cups, cones and bearings sitting in a sealed unit.
Into the head tube and fork the house is squeezed for fixed bearings see figure 37 . With the ahead set is the construction of the headset clearly different, see Figure 38. The inside head tube of the front fork for this headset is not provided with screw thread. Internally a rigid lock is inserted into the head tube. The upper headset cup is pushed onto the fork tube. Then the spring washer are the top seal, assurance, any cable guide and the special stem pushed onto the fork tube.
The whole is set with an Allen screw and the rigid lock secured. This will firmly put both primary and stem. The stem is then fixed with a separate bolt in order to prevent it from twisting. By using the spring ring the bearing is adjusted free of play, even under widely varying loads.
For example, if pressure forces the lower bearing 1mm, the upper headset cup would normally also 1mm to emerge which gets the upper bearing clearance.Through the use of the cup spring, the ball head is, however, continuously pressed against the bullets. Like the brackets and hubs , now also headsets are being used with fixed bearings and cylindrical applications.
The bearings are pressed into the head tube.
The cylindrical front fork is secured in the same manner as in the Aheadset.
These bearings are maintenance free. If they do not function properly, they have to be replaced entirety. (See Figure 39) for a typical seal of the steering head bearing.
With servicing, check that the head tube bearing is still running smoothly and without play.
If this is not the case, the bearing must be dismantled and the defect to be remedied.
Worn parts must be replaced. It is in any case advisable to clean the bearing well, to replace the balls, and to adjust the bearing again.
If running surfaces of the cones and cups exhibit irregularities should also be replaced.
In more expensive headsets is the tread of the cups more hardened and polished pure so they exhibit less wear and run smoother.
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