Is it actually very difficult?! A handy special hammer for the stem bearings that greatly affect handling?

When tuning the suspension, including brakes, wheels, tires, and suspension, it's crucial not to forget to check the steering stem bearings. If the handlebars don't move smoothly from right to left, or if there's a notch due to wear, the bearings need replacement. However, pressing new bearings onto the stem shaft can be difficult. This is where a bearing race hammer comes in handy. The key feature of this tool is its "long hollow shaft."

## Checking Stem Bearings is Easier When the Front End is Removed

You can sometimes notice stem bearing issues just by turning the handlebars fully left and right with the front tire on the ground. To eliminate the influence of the rider's weight, it's best to check while standing next to the bike rather than sitting on it. If your bike has a center stand, try lifting the front tire by applying weight to the rear of the seat and then turning the handlebars left and right.

With the tires and front forks attached, inertia affects the steering. By removing them and turning the handlebars with only the steering stem, even minor indentations become more noticeable. If you've already removed this much, it's a good idea to clean and grease the bearings, even if you don't feel any issues.

Whether it's an older model or a current one, a scooter or a big bike, with conventional or upside-down forks, steering stem bearings are always incorporated where the tires, wheels, and suspension connect to the frame.

No matter how much the rigidity of the frame or front forks is increased, the structure incorporating ball bearings or tapered roller bearings between the steering stem and the frame's head pipe has remained unchanged for a long time.

It's also well-known that stem bearings are susceptible to damage from falls or road impacts, and indentations on the race surface can negatively affect handling.

While it's become common, especially for sports models, not to have a center stand, making it difficult to lift the front tire, lifting the front end is still the best way to check the condition and integrity of the stem bearings.

If the bearing damage is minor, it might be difficult to notice with the front tire on the ground. However, lifting the tire and relieving the load will make any sticking in the bearings more apparent. It's even more recommended to check them when you remove the front forks for an oil or seal change.

When you remove the tires and forks, which act as "weights" when turning the handlebars, the inertial mass decreases, making it easier to detect even slight abnormalities in the bearings. If you've removed the front forks, it's not a significant hassle to remove the top bridge and steering stem for a direct visual inspection. However, to check the smoothness based on the current tightness of the stem nut, it's best to turn the handlebars with the forks removed.

## Knocking Out Outer Races Pressed into the Head Pipe

Unfortunately, if the stem bearings have defects like race indentations, they must be replaced. The outer races are pressed into the frame's head pipe, and the standard method is to insert a suitable rod from the inside of the pipe and tap the inner edge of the race to push it out.

The key point to be careful about during this process is **"to strike without tilting the race."** In reality, it's unavoidable that the race will tilt somewhat if you strike one point. However, by changing the striking point to different locations along the inner wall of the head pipe, you can minimize the tilting of the race. Since the race material is much harder than the frame material, if you ignore this and continue to strike only one spot, the race holder part of the head pipe could deform into an oval shape, making it impossible to press in a new race – a worst-case scenario that requires careful work.

By the way, if the outer race has indentations, it's essential to replace the inner race as well. The inner race for tapered roller bearings has tapered rollers and a cage, making the race surface difficult to see. However, if there are linear indentations on the outer race, there will definitely be indentations on the inner race, so reusing it without replacement is strictly prohibited.

The inner race pressed into the head pipe is knocked out using a rod longer and harder than the head pipe (here, the inner pipe of a swingarm pivot from a scrapped bike). This method is only applicable when the inner diameter of the inner race is smaller than the inner diameter of the head pipe, and the striking rod can catch the inner edge of the race.

The inner race is removed by inserting a rod from the top of the head pipe, and the lower inner race is removed by inserting the rod from the bottom. If you concentrate on striking one spot, the race will tilt and the head pipe's race holder will deform. Therefore, strike in several places along the inside of the head pipe, gradually moving the striking point.

Always replace the inner and outer races as a set. The inner race of a tapered roller bearing has a cage and tapered rollers, making the race surface difficult to see. However, if a large force, such as from a fall, causes indentations on the outer race, the inner race will also be affected.

## Races Pressed onto the Bottom of the Stem Shaft are Difficult to Remove and Install

When removing the inner race pressed onto the stem shaft, a chisel is typically used. Securely fix the stem in a vise and carefully tap to remove it without damaging the lower bracket or stem shaft.

If there is a dust seal between the inner race and the lower bracket, it is highly likely to be damaged by the chisel. When ordering stem bearings, it's advisable to also obtain the dust seal so you won't be flustered if it gets damaged during the work.

The reason why people are tempted to reuse the inner race when replacing stem bearings is that the inner race pressed onto the steering stem shaft is **"difficult to remove and difficult to press in."**

Depending on the motorcycle model, the stem shaft that passes through the head pipe can be nearly 200mm long. Removing the inner race pressed into its base requires more than just general hand tools. While there are specialized pullers for tapered roller bearings, they are quite expensive for amateur mechanics.

Therefore, the common practice is to use a chisel to strike the junction between the bottom of the inner race and the lower bracket, gradually removing it. However, similar to the outer races pressed into the head pipe, due to the difference in hardness between the stem shaft and the race, if the race tilts, it can easily dig into the stem shaft.

For this reason, when striking the race, you must move the chisel along its outer edge, gradually shifting it to remove it.

And the task that is even more difficult than removal is pressing the new inner race onto the stem shaft.

## Bearing Race Hammer is Convenient for Accurately Pressing in Races

The bearing race hammer sold by Astro Products. The attachment that contacts the inner race of the bearing is made of aluminum, and the shaft that fits into the attachment is made of steel. While some people use old inner tubes or PVC pipes purchased from home centers for this task, the key point is that the attachment is made to fit the size of the inner race.

The black attachment is φ32mm, the gold is φ35mm, and the red is φ44mm. They are used according to the size of the inner race to be pressed in.

The end of the shaft has a conical cap, and the force from striking the hammer is evenly transmitted to the entire circumference of the attachment, which helps prevent the inner race from tilting. If you optimistically think it will flatten out even if slightly tilted, the race can dig into the stem shaft, leading to an irreparable situation.

Select an attachment that does not contact the race surface where the balls roll before pressing.

Be careful not to let the attachment shift as you slide the shaft through the stem and strike the conical part at the top straight with a hammer. Placing it directly on the floor can cause the stem to jump due to the impact or absorb the striking force. Therefore, work with the stem securely fixed in a vise.

The key points to consider when pressing the inner race onto the stem shaft are "do not tilt the race" and "do not scratch the race surface."

If the race is pressed onto the stem shaft while tilted, the surface of the shaft will be scraped. If you continue to strike in this condition, not only will the fit become loose, but fragments of the scraped shaft may get caught between the bottom of the race and the lower bracket, preventing proper contact and potentially causing the race to stop slightly elevated.

If the rotating surface of the inner race is tilted relative to the outer race, the gap between them will not be uniform when the front end is assembled, and the bearings will not function correctly, rendering the replacement pointless.

It is also important to strike without scratching the race surface. Similar to pressing wheel bearings into a wheel, a suitable "collar" is needed when pressing the inner race onto the stem shaft. If this collar contacts the race surface on a ball bearing or the tapered rollers on a tapered roller bearing during pressing, it can cause damage, which would negate the purpose of the replacement.

Experienced mechanics often devise original tools to avoid damaging the inner race while working with long stem shafts. However, specialized tools do exist. One such tool is the **"bearing race hammer."**

This tool is a combination of a ring-shaped attachment that matches the size of the bearing's inner race and a metal pipe. It is sold by Astro Products.

As a dedicated tool, it comes with three types of attachments with diameters that match commonly used stem bearing sizes. Since they contact the inner edge of the race without touching the race surface, there's no risk of scratching.

Another noteworthy feature is its 370mm long hollow shaft, which can be inserted over the long stem shaft, and a tapered cap on the opposite end of the shaft.

The tapered cap on the shaft, when fitted onto the stem shaft, acts as the center. Striking this cap with a hammer transmits the impact force evenly to the inner race through the attachment.

Many DIY mechanics have likely struggled with how to press in the inner race when they don't have a pipe longer than the stem shaft. This tool allows for pressing in the race **"without tilting"** and **"without scratching."**

## Specialized Tools are Effective for Amateurs to Reduce the Risk of Failure

While maintenance tasks like adjusting drive chain slack or working the brake caliper pistons can also lead to mistakes, replacing stem bearings is actually a task with a higher risk of failure. The biggest reason for this is often the lack of proper tools to perform the work safely.

The bearing race hammer lacks the versatility of screwdrivers or wrenches, and stem bearing replacement is not a frequent task. Therefore, even if you understand its usefulness, it's understandable to hesitate to purchase it. However, as mentioned earlier, steering stem bearings are critical components that significantly influence a motorcycle's handling stability.

If you feel an unusual sensation in the handlebars and plan to have a motorcycle shop diagnose it and potentially replace the bearings, the work and tools introduced here are unnecessary. However, if you lift the front wheel and feel a "clunk" when turning the handlebars, and you want to handle it yourself, it might be worth considering acquiring a specialized tool to minimize the risk of failure.