Suspensions are regularly overhauled to ensure stable performance at all times. How does suspension overhaul proceed in a professional store? Let's take a glimpse at this part of the process and use it as a reference for DIY maintenance.
Photography/Technix: https://technix.jp/
Oil Seal and Dust Seal Kits
Technix is a professional suspension overhaul store that basically overhauls any shock unit that can be overhauled and for which parts can be procured, regardless of whether it is an on-road, off-road, or old motorcycle. Technix offers oil seal and dust seal kits made by SKF of Italy. Compared to the manufacturer's OEM oil seals and dust seals, these kit parts are characterized by reduced friction loss. If there is a kit that fits your motorcycle, I would like to try it.
Dimensional control regardless of model
We, Sunday mechanics, pull out the part numbers from the parts list of compatible models and order the parts. It is common practice for us Sunday mechanics to order parts from the parts list of compatible models, but in suspension pro stores, compatible parts are controlled by parts supply from suspension manufacturers and parts dimensions. When overhauling an upright fork, the inner tube side slide metal and bottom case upper side receiving metal are replaced with new parts.
Thorough rust check and bend distortion check
According to the manufacturer's original service manuals (data varies by model and manufacturer), inner tube bends are within 1/100 mm; some older motorcycles from the 1970s and earlier are marked for parts replacement if the inner tube bend exceeds 3/100 mm. In general, inner tube accuracy is extremely high. It is a matter of course that the manufacturer's OEM new parts have almost zero runouts. Even at Technix, bent inner tubes are replaced with new parts.
No bents but rust...
If the model has been left unattended without being ridden for a while, rust may form on the inner tube depending on the storage environment! It is not uncommon to find cases such, where the rust is severe even though the motorcycle is indoors in a humid place, even though it is fine when stored in an open-air store with only a body cover. If deep rust is found, the inner tube is replaced, but when no replacement parts are available, the motorcycle may be repaired with a request for re-hard chrome plating treatment. The same goes for rust on the rear suspension damper rod. Surface rust is polished and finished on a lathe in the lab.
Change of spring setting
For competition motorcycles, it is natural to be asked to change settings. Damping force is changed by adjusting the shims on the damper valve, but when changing the spring rate, the spring rate is measured from before to after. This quantification makes it easier for the rider to make a decision.
Meaning peeking into the bottom case.
On both street and competition motorcycles, look into the bottom case for upright forks, and into the outer tube for inverted front forks, and check for distortion in the line of light you hold up. The cause of most cases of partial malfunction seems to be dents caused by a fall. If the problem can be corrected, it is good, but if not, parts will have to be replaced.
- Point 1: Professional work procedures and finishes are a role model for Sunday Mechanic.
- Point 2: "Highest performance" can also be obtained through professional work & finishing.
By dividing the work into parts, technology is pursued and refined in each area. As a result, the performance of complete machines evolves day by day. As you know, specialists and special stores for various parts have emerged in the motorcycle industry as well, but the division of labor in the Japanese motorcycle scene is not yet as advanced as in Europe and the United States. In Europe and the U.S., there are many specialized manufacturers who seem to think, "How can they do business if they only deal in this kind of thing? In the field of single parts, there are well-known manufacturers specializing in pistons and connecting rods for engines, as well as gasket makers who sell various gaskets as kits. For electrical parts, there are IG coil manufacturers, CDI manufacturers, and transistor ignition unit manufacturers. For motorcycle body parts, there are manufacturers specializing in internal parts for meters and damper rubber parts used in various parts of the motorcycle body.
The world's leading motorcycle manufacturers were concentrated in Japan. There are many parts makers in Japan, but they are only subcontractors to complete vehicle makers, and therefore there are very few cases where they directly sell parts to us, the users.
However, the situation of overseas special makers is different from that of Japan, and since there are few complete makers to begin with, they have had to follow their own path as parts makers. In this sense, I think that if Japanese high-performance parts makers "sell sought-after parts to individual users around the world" through the Internet, they can do business not only with Japanese users but also on a global scale.
In terms of division of labor, it is the suspension pro stores that we can rely on. It is Technix that provides us with high-performance products through its worldwide network. The more you know about motorcycles, the more you ride, the more you understand the importance of suspension. As evidence, the number of riders requesting overhauls from Technix is increasing every year, regardless of category. In addition to suspension overhauls for competition models (road racers and motocrossers), in recent years, there have been many requests for overhauls of OEM shock units (especially rear shocks), and the company has developed original countermeasure parts for shock units that are frequently inquired about. The company has also developed its own original countermeasure parts for the shock units for which it receives many inquiries. The company is also actively working to update parts that produce benefits such as improved overhaulability. One example is the overhaul and update of the Öhlins twin shocks used in the Yamaha XJR series. By replacing them with sealing heads developed by Technix, not only is performance restored, but overhauls can be easily performed later. And since the appearance of the parts will remain the same, this is the best option for XJR series fans.
This digest report on front fork overhaul is only a reference for Sunday Mechanics. We hope to see more and more specialization in other industries as well.