Is your motorcycle feeling difficult to ride lately!? If so, check the steering stem before your riding technique.

As the driving school teaches, "motorcycles turn in the direction the rider is looking," and for lane changes and cornering, motorcycles rely more on eye movement and body weight shifts than consciously turning the handlebars. The steering stem bearing is a crucial part for smooth riding. If you feel any discomfort in your handling, not just during cornering but also when riding straight, check the condition of your steering stem bearings in addition to tire pressure and your own riding technique.

Steering Stem Bearings are the Most Important Part

The steering stem connects the frame and the front fork, and the steering stem bearing allows it to rotate smoothly when turning the handlebars left and right. Motorcycles maintain balance by making small, continuous movements of the handlebars even when riding straight, and if the stem bearing races have indentations, it can cause the handlebars to shake.

Many of you may have experienced riding a bicycle with no hands as a child, once you got a little used to it (though it's not recommended). You were probably impressed that the bike would go straight without falling over as long as you were pedaling, thanks to the caster angle of the front fork and the trail of the front wheel.

However, at that time, the handlebars were not actually fixed straight; they were likely moving finely left and right (turning) as you rode. The steering stem bearing is the key component that allows the handlebars to make these micro-adjustments while riding.

The steering stem bearing connects the front fork to the frame, transmitting handlebar inputs smoothly and accurately.

The importance of stem bearings is similar for both bicycles and motorcycles. Properly adjusted bearings create natural self-steering, allowing the motorcycle to turn exactly as the rider intends, in the direction of their gaze.

On the other hand, wear, improper tightening, or indentations and damage to the bearings or bearing races can lead to handlebar stiffness, vibrations, and in the worst case, behavior close to loss of control.

Many riders diligently check their tire wear and pressure, but few have ever checked their stem bearings.

To determine the condition of your stem bearings, lift the front wheel off the ground and slowly turn the handlebars left and right. If the handlebars turn smoothly throughout the entire range of motion from full lock to full lock, the stem bearings are likely in good condition.

Conversely, if you feel any stiffness or a "clunk" as you turn the handlebars, it indicates a problem or trouble with the stem bearings or races. Damaged stem bearings will not recover on their own, so proper maintenance is necessary.

What's the Difference Between Ball Bearings and Tapered Roller Bearings?

An example of a tapered roller bearing used in steering stem bearings. The rollers arranged in the cage of the inner race are conical rather than cylindrical, allowing them to withstand greater loads than ball bearings. In addition to steering stems, they are sometimes used in wheel bearings on Harley-Davidson and BMW motorcycles.

There are two types of stem bearings for motorcycles: "ball bearings" and "tapered roller bearings," each with the following characteristics:

● Ball Bearings

Advantages:
1. Low rolling resistance, resulting in light handling.
2. Low cost and high mass production suitability, making them common as original equipment on small-displacement motorcycles.

Disadvantages:
1. Point contact leads to low load distribution capacity.
2. High contact surface pressure makes them prone to indentations.
3. Wear can cause "stickiness" in the steering.

● Tapered Roller Bearings

Advantages:
1. Line contact provides excellent load distribution.
2. High rigidity.
3. High durability and less prone to stepped wear.

Disadvantages:
1. Higher friction compared to ball bearings, tending to make handling heavier.
2. Highly sensitive to preload adjustments, requiring precise setting.
3. Higher cost than ball bearings.

Due to these differences, small-displacement motorcycles tend to use ball bearings, while large-displacement motorcycles often use tapered roller bearings. However, many large-displacement models now also use ball bearings to minimize friction loss.

Replacing Bearings Requires Removing the Entire Front End, Making it a Major Task

To remove the steering stem, you must first remove the front wheel, front fork, brakes, fairings, and meter assembly, and then remove the top bridge. It is crucial to support the motorcycle securely with a proper stand to maintain stability when the front wheel is removed.

Indentations on the bearing races cause stiffness when turning the handlebars left and right, hindering smooth cornering. However, replacing the bearings requires removing the wheels, front forks, and steering stem, so you need to create a safe environment where the motorcycle won't fall over without the front wheel.
If your vehicle has a center stand, you can support it with the center stand and a jack under the engine. For bikes with only a side stand, you'll need to use a maintenance stand and a jack under the engine. Proper preparation of the work environment and support equipment is essential.

Furthermore, if your bike has fairings, you'll need to remove all of them, including fairing stays. Even on naked bikes, you'll have to remove components around the handlebars, such as headlight stays and meters. This requires thorough preparation.
The following points are often the most challenging during bearing replacement:

● Removing the Outer Race

The outer races installed in the frame's steering head tube are press-fitted with very tight tolerances to prevent them from coming loose or tilting easily, making them difficult to remove.
The simplest method involves:
1. Inserting a rod from below the head tube and tapping out the upper race.
2. Inserting a rod from above the head tube and tapping out the lower race.

If the race protrudes from the inside of the head tube, a tapping rod can catch it and facilitate removal. However, if the rod cannot catch the race, specialized tools are required. Also, if the press-fit holder area is deep and the race tilts during removal, it can scratch the inside of the holder. This can make it difficult to press in the new race or cause the burrs from the scratches to prevent proper seating.

The lower outer race press-fitted into the steering head tube. If not regularly greased, the grease on the race surface can wear off, leading to rust. However, the regular pattern of lines is distinct from dirt or rust.

The upper outer race, press-fitted onto the head tube, is removed by tapping it out from below the head tube with a rod and hammer. If the rod doesn't catch the edge of the race, a special tool is needed. Even if it catches, avoid hitting one spot exclusively; tap evenly along the inner circumference of the head tube, being careful not to tilt it excessively.

After wiping off dirt and grease from the race, you can see this. The indentations, spaced according to the roller pitch, create a noticeable step when you run your finger over them, causing the handlebars to catch and not move smoothly. Indentations can be caused by impacts from the road, hard braking, or over-tightening of the stem shaft's top thread or stem nut.

● Removing the Lower Inner Race

Of the upper and lower inner races, the upper one is easy to remove. However, the lower race is press-fitted onto the stem shaft and cannot be removed by simply pulling it by hand.
At a minimum, a chisel is required, and for tapered roller bearings, a specialized bearing remover tool may be necessary.
Similar to the outer race, if the inner race tilts while being tapped out, it can dig into the stem shaft and cause scratches. It is crucial to tap evenly around the entire circumference.

The lower inner race press-fitted at the base of the steering stem shaft. For ball bearings, it's just the race, but for tapered roller bearings, the inner race, tapered rollers, and cage are integrated. A dust seal is present at the bottom of the lower inner race to prevent dirt and water ingress, but rust has formed on the roller surfaces due to insufficient maintenance.

To remove the lower inner race, clamp the stem shaft in a vise and tap the race with a chisel, or use a specialized tool. When using a chisel instead of an expensive specialized tool, tap evenly around the entire race to prevent it from tilting and digging into the shaft.

The cage deformed and the rollers fell out, but the inner race was removed without damaging the stem shaft. Although disassembled with a chisel, the dust seal is normally integrated with the race.

The upper and lower steering stem bearings, the upper cover, and the special lock nut for the stem nut are replaced. The upper cover has a dust seal attached to its inner side.

Don't Forget to Grease When Installing New Bearings

The most important point when installing new bearings is "do not press them in at an angle."

Bearing races are made of chrome steel, which is much harder than the frame's steel or aluminum. If a race is pressed in at an angle relative to the bearing holder or stem shaft, it will dig into the frame or shaft.

It's tempting to think, "Even if it tilts a little, I can correct it by tapping the other side," but if a tilted race gouges the bearing holder or stem shaft, it creates burrs. If you continue pressing with burrs underneath, the race may not seat properly.

Also, if you hit the race surface where the balls or tapered rollers move during press-fitting, you'll scratch the new bearings. Therefore, care must be taken in selecting the tools used.

Pressing the new outer race into the frame's steering head tube. To avoid scratching the race surface where the rollers contact, use a bearing installer that contacts the outer circumference of the race. The taper of the installer is designed to avoid contact with the race surface.

If the outer edge of the bearing installer interferes with the head tube holder, use the old outer race as a shim to press in the new race. Avoid hammering forcefully, which can cause it to go in crooked. Tap lightly around the entire circumference of the race until it's partially seated.

A grease packer is useful when you're unsure if grease applied to the outside of the tapered rollers is adequately reaching the rollers and race surfaces that require lubrication. By placing the inner race inside and pressing down with a handle, grease is forced from the race surface to the rollers, ensuring complete coverage.

Spread the grease that has reached the roller surfaces through the cage from the race surface. Apply grease not only to the inner race but also to the outer race press-fitted into the steering head tube.

Use a pipe with an inner diameter larger than the stem shaft that does not interfere with the inner race cage to press it in. Do not hammer it in all at once; gradually tap it while confirming that the lower inner race is not tilted.

The First Step is to Identify Your Bike's Bearing Type

As explained, steering stem bearings are not attached with bolts or nuts, so their removal requires tools beyond basic hand tools and involves specific techniques.

You can easily check for stiffness by lifting the front wheel and turning the handlebars left and right. Conversely, if you cannot lift and support the front wheel, it's best not to consider replacing the stem bearings yourself.

Furthermore, if you remove the steering stem and then find you cannot remove the outer or inner races, it's a worst-case scenario. Therefore, it's recommended to first research your bike's stem bearing type, removal procedure, and difficulty level using a service manual or online maintenance articles.

The example shown here is for a motorcycle using tapered roller bearings, which were successfully replaced using tools like a chisel and stainless steel pipe.

In actual bearing replacement, the tightening torque of the stem shaft's top thread and the stem nut that secures the top bridge are crucial. However, before that, it's important to assess whether you have the necessary tools, environment, and skill level to perform the bearing replacement.

The upper inner race is simply placed inside the outer race, and the stem shaft inserted from below the head tube passes through. The preload applied to the stem bearings changes with the tightening torque of the nut that secures the stem shaft. If the preload is too weak, the steering stem can wobble front-to-back during braking, causing race indentations. Conversely, if it's too strong, it increases friction when turning the handlebars and also raises contact pressure, leading to indentations. Therefore, tighten according to the method specified in the service manual.