The previous time we talked about transmission, today we talk about "bearings".
The bearings are in the key places of the bicycle: at the steering. In the bottom bracket, in the hubs and in the links of bi-cushioned bikes. We learn to understand if and where it is necessary to intervene.
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To understand if the steering bearings are to be adjusted, we must clamp the front brake, then we put our thumb and index finger on the upper steering cap and, by swinging the bicycle back and forth, we check if the steering has taken play and if it is necessary to intervene, by adjusting the steering or cleaning it or replacing it.
Now let's move on to the cranks, also these operating with a slight movement, as if we were pushing on the pedals, let's see if there is a need to intervene here too with a cleaning or a replacement.
To examine the hub of the front wheel we take the upper part of the tire in the palm of the hand and by swinging the wheel we feel if there is play. The same thing also applies to the rear hub. We do another examination by listening to the rolling noise of both wheels to perceive if there are any suspicious rustles or squeaks. Obviously the rear wheel must be rotated forward by dragging the chain and all the play of the sprocket cassette.
As for the suspension link, you take the wagon and flex it left and right to identify if there are any games on which to intervene.
To intervene on the "play" of the steering and reduce the oscillation: we loosen the two screws of the handlebar stem and we intervene with an Allen screw on the head screw on the cap that serves to amass the whole department. We squeeze until we feel we have reduced the "game". At this point the front wheel hits the ground and we hear again if the bearings have gone into section. Then, after having centered the wheel with the optical caliper, let's go back to tightening the screws. A recommendation: the first part can be done by hand with a normal Allen key, while the final tightening is important to do it with a torque wrench set at 5/6 Nm In any case, for those who do not have this tool, the suggestion is not to tighten too much. . The intervention on the bottom bracket and on the hubs should be done in the workshop.
The torque wrench (or torque wrench) is a controlled tightening wrench used for tightening screws, nuts and bolts to the right torque value. It resembles the ratchet and is used with sockets, but contains a mechanism capable of signaling the achievement of the set torque value, thanks to a click or a pointer that indicates the instantaneous tightening value on a graduated scale. The units of measurement are numerous, usually newton per meter (N · m) in the metric system, pounds-force per foot (lbf · ft) in the imperial system.

It was invented by Conrad Bahr in 1918 while working for the New York City Water Department, and was designed to avoid excessive tightening of the water supply bolts and underground steam pipes.
The torque wrench is used when tightening is important in order not to damage the thread or to ensure homogeneity of the load in a mechanical part held in place by several screws or bolts. An example is the cylinder head for the engine.

As for the steering, for those who have the skills to extract the bearings, let's see how to operate the bearing maintenance.
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We take the bearing in hand and with a razor blade we remove the shield (photo 08) from both sides to expose the balls. First we spray a detergent inside and wipe with a sheet of kitchen paper. At this point it would be better to use a compressed air gun to perfectly remove any residual dust or other. The last step is lubrication, not with oil but with grease that we will insert inside. There are guns made specifically, or, in the old way, simply with your finger. Once the excess grease has been removed, reinsert the shields. The last operation is to check also the lateral wear by sliding the central part and observing if the rolling is homogeneous.
As for the suspension joints, things get more complex because every company has their own way of inserting the bearings and protecting them, so the do-it-yourself maintenance is quite difficult and my advice is to go to a specialized mechanic.
To conclude, I can tell you that the first step for maintenance is to "listen to your bike", in the cars we have lights that flash and signal faults and anomalies, the bikes do not have them, so "listen to it", the bike "talks to you ”And therefore the important thing is to perceive: vibrations, noises and rubbing in order to intervene in the shortest possible time.
Bearings history
Drawing by Leonardo da Vinci (1452-1519). Ball bearing study.
Already Leonardo da Vinci (1452-1519) during his studies concerning friction sensed the possibility of creating a sort of primitive bearing (see figure), but the first ball bearing patent was proposed by Philip Vaughan of Carmarthen (Wales) in 1794. Another patent was filed on August 3, 1869 by Jules Suriray, a Parisian bicycle mechanic, who used these bearings on the bicycle that won the first edition of the Paris-Rouen race in November 1869.
The development of current bearings was by Friedrich Fischer in 1883. The evolution and large-scale industrial production was due to Henry Timken, as regards roller bearings, who founded the Timken Company in 1899 and to Sven Gustaf Wingqvist one of the founders of SKF in 1907 as well as the RIV of Villar Perosa (Roberto Incerti & c Villar Perosa) who in partnership with the Agnelli family began manufacturing ball bearings for bicycles in 1906. RIV was later incorporated into SKF.

