Not too light, not too heavy. It’s the hardest part of bike maintenance.!?Steering head adjustment tips

The caster angle of the front fork is an important factor in achieving both straight-line stability and cornering performance. And the steering stem bearings that connect the front forks to the frame are deeply involved in smooth operation. Despite this, the procedure for tightening the stem nut varies from model to model and is more severe than you might imagine, so be careful.

Scooters are the ones to watch out for. Racing small displacement vehicles is surprisingly vulnerable.

If there are no dents on the bearing race, it will not get stuck when turning the steering wheel to the left or right. However, if the grease gets old, its rust-preventing ability may decrease and rust may occur on the race, so it is advisable to clean and grease the race regularly. The ball bearing of the current car can be attached and detached by the bearing + retainer, but the 1970's car has one bearing ball on each race, so when the steering stem is pulled out, the lower bearing ball falls apart. So when you remove the stem nut, you should put a tray under the stem to catch the falling bearing balls.

The bearing on the upper side of the head pipe is recovered with a magnetic pick-up tool. If the same diameter balls are used on both the upper and lower sides, it is recommended to check how many of each are incorporated before removing them to avoid confusion during assembly.

When you turn the handlebars left or right, the direction of the front wheel changes smoothly thanks to the stem bearing built between the head pipe of the frame and the steering stem. If there is a problem with this bearing, not only will you not be able to steer smoothly, but you may also feel uneasy when driving straight.

As you know, there are two types of stem bearings, ball bearing type and tapered roller bearing type, and both of them work by being sandwiched by bearing races which are bearings from the top and bottom. Stem bearings, which accept the force applied to the axial direction of the stem pipe rotating at a certain angle, are a type of thrust bearing.

When we talk about stem bearing damage, we usually refer to the condition where the bearing is dented by the impact when it is pressed against the race with high force, and the bearing cannot roll smoothly over the race. When a tire picks up an uneven surface, the impact is transmitted from the wheel, through the front fork and steering stem to the stem bearing. As the impact is absorbed by the tire and front fork, the corner is removed, but the part that cannot be absorbed is directly transmitted to the stem bearing, and the bearing bites into the race, resulting in a dent.

It is unlikely that you will get a dent in your race from a sudden braking during normal driving. On the other hand, however, it can be surprisingly easy to get a scratch. A typical example of this is a standing scratch. Standing injuries often occur when riding at low speeds or when parking, but many riders seem to fall over while holding the front brake and turning the handlebars to the left or right (more like left) when they go "OTT...". When they finally fall to the ground, the steering stem is in contact with the frame's handlebar lock and the weight of the vehicle is added to the head pipe.Strong pressure, not absorbed by the tire or front fork, can cause the bearing to bite into the bearing race, leaving dents.

Even if it's not a standing accident, the stem bearings can be damaged by the rough handling that only small-displacement vehicles can provide. You may see scooters parked with the front wheel against a stop sign, or changing direction by locking the handlebars full left or right at a store or home bicycle parking lot.

The light weight of the car and the light steering wheel tends to give momentum, but if the steering stem hits the handlebar stopper too vigorously, there is no place for the inertia force to escape and the bearing can damage the race. The front forks have less stroke than those of medium and large vehicles and are more prone to bottoming out, which is another reason why the stem bearings are easily damaged.

Concentrate your nerves on tightening the stem nut after changing the race and greasing

If there is no rust or dents on the surface of the bearing race, remove the old grease, apply a generous amount of new grease, and line up the bearing. We recommend using a lithium or urea-based grease that has both extreme pressure resistance and water resistance. Using a grease gun that makes it easy to aim the grease at the application area will help prevent over-application.

After greasing the races that are press-fit into the head pipe of the frame, assemble the bearings lined up with the steering stem races into the frame to prevent them from falling out. If you are working alone, it is a good idea to remove the steering wheel and headlight beforehand, or hang them on the frame to keep them out of the way.

If the bearing race is dented, it needs to be replaced. If it is not dented, it needs to be cleaned and greased to get smooth handling again. This is one of the most delicate and difficult parts of bike maintenance.

The bolts and nuts used to secure and assemble parts may be specified in terms of torque, but basically they serve their purpose by being tightened so that they do not loosen. On the other handThe stem nut must be tightened so that the steering stem does not rattle, but if it is over-tightened, not only will the steering wheel become reluctant to move, but it may also damage the bearing race.It is the same for all models. For this reason, the service manual shows that the procedure for tightening the stem nut varies considerably from model to model.

For example, the service manual for a 50cc scooter that uses ball bearings states that after tightening the stem nut to the specified torque of 11Nm and moving the steering stem to the left and right several times, loosen the stem nut until it can be turned by hand./It states to back off 8 turns and then tighten the locknut that is assembled over the stem nut to the specified torque of 68Nm. The procedure is similar to opening the rotary lock of a safe.

On another 1000cc supersport model, the stem nut is to be tightened to 52Nm and then completely loosened after moving the steering stem left or right a few times, and then tightened to 14Nm. Then tighten the top nut to 115Nm after the top bridge is fitted. Scooters don't have a top bridge, so the torque values required for tightening are different, but it's clear that both bike manufacturers and themselves have various measures in place for dealing with stem nuts that can't just be tightened.

Not too heavy, not too light. If it doesn't feel right, you need to have the patience to repeat the adjustment.

Always use a hook wrench or ring spanner to turn the stem nut. Screwdrivers and punches cannot be used for delicate adjustments, and a thin hook wrench can be used on the nut groove after the top bridge is assembled. The ring spanner can be used for a wide range of nut diameters because its mouth width can be adjusted with the worm gear like a monkey.

After understanding that the procedure of tightening the stem nut is not uniform from model to model, let's think about how to handle the nut after greasing the stem bearing. If you already have a service manual for your car, the most reliable way is to follow the procedures and values described in the manual. However, if you are following the service manual, a torque wrench is an essential item. In the case of the 1000cc Supersport model introduced in the previous section, a torque wrench capable of measuring torques from as little as 14Nm to as much as 115Nm is required, which alone is a lot of preparation.

If you don't have a torque wrench, or if your model doesn't have a specific tightening torque listed in the service manual, the previous example will help you. In other words.With the stem nut tightened, operate the steering stem to the left or right to blend it in, then loosen it once and tighten it with less force than when you first tightened it.This is the way to do it.

Even if you tighten it strongly at first, it is 11Nm in the example of the scooter, and 52Nm even in the super sports, so you don't need the force like tightening the axle nut of the front and rear wheel, rather, if you tighten it with ridiculous force, you may damage the bearing race with that force, so be careful.

After tightening the stem nut, loosen the stem nut as much as possible to get smooth handling, but be careful not to loosen it too much or you may get a rattle between the bearing and the race when you apply the brake. It is also necessary to imagine the weight of the steering stem after installing the front fork and the tire, because the inertia force when you turn the steering wheel increases. As a personal rule of thumb, when the stem nut is tightened, the friction should feel a little large, so that the stem will not be too light even after the fork and tire are installed.

Even if you are satisfied with the tightness of the stem nut, the weight of the steering stem changes when the top nut is tightened after the top bridge is set. The previous Super Sport has a stem nut of 14Nm while the top nut on the top bridge is 115Nm, so obviously the entire steering stem is set by using the tightening torque of the top nut.

Tighten the top nut, install the front fork and tire, try turning the handlebars left and right with the tire floating, and if it is finished not too light and not too heavy, the work is done, but it is not always decided at once. Something like.If it doesn't feel right, don't hesitate to loosen the top nut and adjust the stem nut to check the friction.. It is a hassle to loosen the parts again once assembled, but let's work steadily with the understanding that comfortable maneuverability can be obtained by fine tuning.