The Stem Bearing is Important and Delicate. This is a Useful Tool for Removing the Lower Inner Race!

Whether it is a 50cc scooter or a 1000cc supersport, the condition of the steering stem bearings is an important factor in determining handling. Bearings that have been damaged by impact from a fall or by running out of grease due to lack of maintenance need to be replaced, but it is often difficult to remove the lower inner race that is press-fitted onto the stem shaft. In such cases, a dedicated puller or remover comes in handy.

When replacing stem bearings, replace the outer and inner as a set.

Damage to the stem bearing may not be noticed while it is mild. If you feel a cracking resistance when you steer left or right with the front tire floating, it is serious.
By removing the front forks and handlebars to reduce the inertia weight, leaving the top bridge and lower bracket alone and moving them slowly, it is easier to feel even the more minor bumps on the racing surface. If you have removed it this far, then visually checking the bearings is not much of a hassle.

Remove the top bridge and lower bracket, and remove the upper inner race. The upper inner race can be easily removed because the shaft only penetrates the lower inner race, which is press-fitted into the stem shaft. There are some indentations where the tapered roller was pressed against the surface of the outer race that is press-fitted to the frame side, but they are not so uneven that they can be felt to the touch.

Motorcycle and bicycle steering wheels incorporate stem bearings to ensure smooth operation of the handlebars.

Whether the bearings installed are ball bearings or tapered roller bearings, stem bearings that are damaged for various reasons must be replaced. Uneven race surfaces on which the bearings rotate can adversely affect handling by creating resistance or catching when turning the handlebars, as well as causing the deteriorated wheel bearings to rattle and cause friction loss.

While ball bearings used in wheel bearings and other components have an outer race and an inner race that are one piece, stem bearings are characterized by the fact that the outer and inner races are separate components. The basic configuration of a stem bearing consists of an outer race press-fitted into the upper and lower ends of the head pipe on the frame side and a lower inner race press-fitted into the lower end of the stem shaft on the lower bracket. An upper inner race also exists about the lower inner race, but this is not press-fitted, only penetrated by the stem shaft, and is used to adjust the pressure applied to the entire bearing according to the tightening torque of a nut called the stem nut or top thread.

In the case of ball bearings, the outer and inner races are replaced as a set when replacing the ball bearing, although some models can be purchased as separate parts.
In contrast, for taper roller bearings, in which the inner race and taper roller are integrated, the outer and inner races are set as a set of parts.

Lower inner lace that can be difficult to remove

The unevenness of the lower outer race seemed larger than that of the upper, so the upper and lower stem bearings are to be replaced. When replacing the lower inner race, the dust seal (the ring-shaped plastic part on the right) that is incorporated between the inner race and lower bracket should also be replaced.

The stem bearing is the only point of contact between the front fork or front wheel, which weighs several tens of kilograms, and the frame or engine, which also weighs several hundred kilograms. Therefore, the outer race and lower inner race are each press-fitted and fixed in place.

Of these, the lower inner race is the key to the bearing replacement process. Removing the outer race, which is press-fitted into the upper and lower head pipe of the frame, is also time-consuming, but the lower inner race is more troublesome in terms of probability.

The reason for this is the length of the stem shaft into which the lower inner race is press-fitted and the shape of the lower bracket. The procedure for widening the small gap between the lower bracket and inner race with a tagger is described in the bike manufacturer's service manual, but because the lower inner race has a small thickness relative to the inner diameter, it tends to tilt when tapped with a tagger, risking biting into the shaft and causing damage.

To avoid tilting, it is important to strike evenly around the entire circumference of the lace, but depending on the shape of the lower bracket, the tagger may not be able to reach some areas, leaving areas that cannot be struck by any means. Another method is to remove the inner race by cutting it with a sander, but be careful not to damage the lower bracket or stem shaft.

Special puller to pull the lace up over the stem shaft

Hasco stems bearing puller assembled. A chuck in the shape of a hakama is placed over the lower inner race, held in place by a collar, and pulled up from the upper end of the stem shaft with a pressure bolt. The shaft's outer diameter dimension is controlled only in a small portion of the inner race press-fit area, and once the bolt is screwed in a few dozen millimeters, the rest can be easily pulled out.

Observing the root area of the stem shaft, it can be seen that the lower inner race is thinner above the part where it is press-fitted into the shaft. However, this fit is so tight that if you tap it with a hammer, the inner race will bite into the shaft and cause scratches. Even if you tap it little by little while changing the position, the race will be tilted as long as you use a tapered tool, so you can feel the ease of use of the special tool, although it is expensive.

In contrast to pullers dedicated to taper roller bearings, general-purpose types of bearing separators and gear pullers may be useful.
The inside of the plate, whose tightening width changes with two bolts, has a sharp tip like the blade of a canner, which bites into the gap between the inner race and the lower bracket to prevent tilting by touching them from 180° diagonal positions. By tightening the two bolts alternately, the blade bites into and widens the gap, and the inner race may be removed without pulling up from the top of the stem shaft. The stem bearing puller can only be used to remove the lower inner race, while the bearing separator and gear puller can be used to pull out bearings press-fitted into the crankshaft or gears press-fitted into the transmission shaft.

Bearing pullers are useful for such troublesome and lower inner race removal work. The puller introduced here is for taper roller bearings and is a product of HASSCO, which has developed and manufactured many special tools.

As mentioned earlier, a tapered roller bearing consists of an inner tube and a tapered roller in one piece. To be more precise, the tapered roller is positioned by a metal retainer to prevent it from coming apart, and the upper end of the roller hangs on the brim of the inner race, thus integrating the roller into the bearing.

The stem bearing puller made by HASKO is covered with a chuck that conforms to the size of the outer circumference of the tapered roller and locks it, thereby holding the entire circumference of the inner race with even force. In this state, the inner race can be pulled straight upward without tilting by pulling it up from the upper end of the stem shaft with a pressure bolt.

Just as a puller for a hole bearing uses a chuck corresponding to the inner race diameter (axle shaft diameter), a puller for a tapered roller bearing needs a chuck corresponding to the inner race size, and this product comes with three types of chucks.

The fit of the chuck and the rigidity of the tool as a whole are excellent, and it snaps into the firmly press-fitted inner race for easy removal. There is some concern that the chuck may interfere with the protrusion of the handle stopper on the upper surface of the lower bracket, and the price of the tool itself is expensive, but there is no doubt about the performance of the tool.

While stem bearing pullers are specialized tools for taper roller bearings, more versatile specialized tools such as bearing separators and gear pullers may be used. These tools bite into the bearing or inner race with a two-part plate formed in the shape of a peg and apply force evenly while pulling up the bearing or inner race with a pressure bolt. Depending on the model, simply tightening the bolts on the split-type plate can cause the taggane to bite into the gap between the lower inner race and the bracket, causing the inner race to come off.

Even if the position is shifted in detail, only one input can be made at a time when tapping with a tup, which causes the inner race to tilt. In contrast, both the HASKO stem bearing puller and the general-purpose type bearing separator support the outer circumference of the lower inner race at multiple points, so the race does not tilt when pulled up with the pressure bolt.

Unlike general hand tools, specialized tools are often expensive because of their low turnover, and people tend to hesitate to purchase them. However, if the stem shaft is damaged by excessive work, the wound may spread further. If you want to work safely and reliably, it is better to utilize specialized tools.