The steering stem bearing is a critical part that affects the handling of the bike. Whether it is a ball bearing or a tapered roller bearing, a scratched or dented race must be replaced, and the inner race that is press-fitted into the steering stem bearing must be extracted and hammered in to avoid damaging the stem.
There are special tools for this purpose, but there is also a way to ensure that they can be hammered in with a change of mindset.
- Bearing greasing and race surface condition is important
- When there are scratches or dents on the racing surface, don’t hesitate to replace it!
Bearing greasing and race surface condition is important
Even on discontinued and old vehicles, stem bearings are often used in later models, so new parts are often available even if the part numbers are old. OEM parts for mopeds more than 50 years old could be easily obtained.
Smooth steering is a prerequisite for turning at intersections and enjoying cornering on winding roads, as well as for driving in a straight line. To achieve this, stem-bearing maintenance is indispensable. The stem bearings, which are mounted on the top and bottom of the head pipe of the frame, receive the impact from the road surface that is transmitted from the tires through the front suspension, as well as the rotational movement when turning the handlebars from side to side.
If the ball or tapered roller gets caught here, smooth movement is inhibited and discomfort is caused. If the steering wheel gets stuck at a certain angle when cornering, or if the steering wheel is strangely taken up even when driving straight, the stem bearing should be checked. A simple way to diagnose the problem is to float the front wheel with a jack or similar device and slowly turn the steering wheel while the vehicle is unweighted. If you feel a full lock to the left or right and a knack in a specific place, there may be a ding in the race.
There are various degrees of depth of race dents, and if the dents are shallow, they may not be noticed while riding. However, by lifting the front wheel and removing the load, even the slightest dents can be easily identified. If you notice a slight discomfort in the handling, you can use this method to check it.
When there are scratches or dents on the racing surface, don’t hesitate to replace it!
A rubber dust seal is often further set behind the bearing inner race that is press-fitted into the lower part of the steering stem. This seal fits snugly into the inside diameter of the frame head pipe and prevents dirt that is rolled up during riding from adhering to the bearing. The rubber hardens over time, so when the inner race is replaced, the seal should be replaced as well.
When the steering is caught due to race dents, it is sometimes tried to cope by increasing the tightening torque of the stem nut, but this has no benefit even as a temporary measure, so it is necessary to take drastic measures by replacing the bearings. In the case of models that use a ball bearing type (here, a 90cc model from the 1960s, Yamaha HS1), there are three parts: the outer race that is press-fitted into the frame, the bearing, and the inner race that is attached to the stem. In contrast, the tapered roller bearing is characterized by the fact that the inner race and bearing are a single unit.
Since the outer race above and below the head pipe and the inner race at the bottom of the steering stem is press-fitted, the trick in removing and installing them is to use a hammer or bar and strike evenly around the inner and outer circumference of the race to prevent the race from tilting. Care must be taken when removing the inner race that is press-fitted into the lower part of the stem. If a hammer is inserted into the gap between the under bracket and the inner race and the hammer is struck, it may bite into the stem, causing damage.
To avoid such a problem, it is important not to pull out the inner race all at once, but to lift the inner race little by little so that it does not tilt.