Hard chromium plating is used to treat the surface of the brake caliper pistons that transfer power to the front fork inner tubes and brake pads. These parts are very dangerous when they rust and need to be repaired, but if the replacement parts are no longer available or out of print, you're out of luck. In such cases, hard chromium plating is a strong ally in re-plating.
What's the difference between decorative and hard?
Decorative chromium plating is applied to the front and rear fenders, steering wheel pipes, and exhaust system. The lower layer of chromium is plated with nickel, which ensures hardness and luster, and a thin layer of chromium to increase the luster.
In motorcycle parts, hard chromium plating is used for the surface finish of inner tubes and brake caliper pistons. In some cases, it is 100 times thicker and harder, and more slippery than the decorative ones, so it is compatible with parts that come in contact with rubber seals.
Along with painting, "plating" is one of the most popular surface treatment methods for metal parts. Electrolytic treatment, which is carried out in an electrolytic solution containing metal ions, is harder than painting, which uses plastic components as a coating, and depending on the type of metal deposited, a mirror-like luster can be obtained.
Due to the need for extensive equipment and environmental concerns, many of the motorcycle's exterior parts nowadays are painted finishes, and the chromium-plated finishes, which were commonplace on older and out-of-print motorcycles, are now rare.
However, we still use plated finishes on inner tubes and brake caliper pistons. The reason for this is that hard chromium plating is the best surface treatment for these types of chromium plating.
Chromium plating can be classified into two types: "decorative" and "hard". Decorative plating is literally used to enhance the appearance of the vehicle's exterior and is used on exterior parts such as front fenders, steel rims, exhaust system, and rear carriers. There are two types of surface treatment for bolts and nuts: zinc and chromate plating, which is used for ordinary bolts and nuts, and chromium plating, which is used for prominent parts such as the handlebar area.
Hard plating, on the other hand, is used for the inner tubes and brake caliper pistons of motorcycles, as well as for the hydraulic pistons of bulldozers and excavators and the hydraulic cylinders of construction and industrial equipment.
Although the surface of both decorative and hard plating has the same chromium, the thickness of the plating is completely different, from 2 to 100μm for hard plating, while decorative plating is less than 1μm. Due to this difference in thickness, hard chromium plating has the advantage of being harder and more resistant to wear.
This is the ideal surface treatment for the inner tube, which strokes against the outer tube, and for the caliper pistons, which are in contact with the rubber piston seal to transfer fluid pressure to the brake pads without leaking.
However, even though the thickness of the plating film is far thicker than that for decorative purposes, when observed at the microscopic level as a characteristic of plating in general, there are very small pores on the surface. Therefore, if moisture penetrates through the pores, it may cause rust to form on the underlying metal material itself.
However, because of their thickness, water evaporates at a higher rate before it reaches the metal base, and both the inner tube and caliper pistons are in contact with fork oil and brake fluid, which are not water, so they are certainly more resistant to rust than fenders and wheel rims.
POINT
- Point 1 - There are two types of chromium plating: decorative and hard.
- Point 2 - Hard chromium plating has a thicker coating, which makes it harder and more resistant to wear.
If you have new parts, that's a good thing.
The rust growth process starts out as point rust and then grows like a spider's web on the base metal to break through the hard chromium layer. Applying a wax or coating may help, but the first thing to do is to not leave the motorcycle wet or store it in a humid area.
A rusted piston where the caliper seal was in contact with the piston. On the right is a Kawasaki GPZ400F for the overseas market, the caliper itself was different from the Japanese version, and the pistons were different. The one on the left is an Estrella with a different caliper design, but the pistons were the same size. We are lucky if we can use these genuine parts.
However, if the inner tube and the caliper piston are stored in the rain or left unattended for a long period of time, there is a risk that the oil on the surface of both the inner tube and the caliper piston will be depleted, and the moisture in the air will gradually penetrate deep into the plating layer. In this case, the chromium plating will not rust, but the iron inside will.
It's tricky when the inner tubes and caliper pistons get rusty. If the rust is detected at the slightest point, it can be removed by scrubbing with fine steel wool. However, if the rust has grown out of the base material and has deteriorated to the point where the plating layer comes off, there's nothing you can do about it.
In the case of the front forks, there is still room to save the rust that has developed above the stroke area where the oil was deposited. It can be saved by wiping off any moisture that is already present in the forks to prevent it from occurring in the stroke area.
Surprisingly, the inside of the fork boot is often overlooked. You'd think the inner tube would be better protected than an exposed motorcycle, but the less you ride, the more water will remain inside and become a breeding ground for rust. Also, be careful of the inner tube insertion type headlight brackets, which are common on older and out-of-print motorcycles. The headlight brackets sandwiched between the top bridge and under bracket are out of the front fork's stroke range, but if the inner tube rusts and sticks inside the brackets, it will be very difficult to pull them out of the trident.
Caliper piston rust is the only way to replace the pistons, no questions asked. As the brake pads are reduced, the caliper pistons will gradually protrude and stop in their tracks. The pistons are coated with a hard chromium-plated surface, but the scraped pad dust mixes with moisture and continues to adhere to the pistons, causing them to rust. If your motorcycle is ridden regardless of the weather, it's more prone to rusting.
If your inner tubes and brake caliper pistons have rusted out, your best bet is to get OEM parts. At this time, you should also replace any oil and caliper piston seals that may have been damaged by rust at the same time.
However, depending on the model and year, it may be impossible to find genuine new parts for some models and years. In this case, you can try to find a part for a different model with a different part number. It's also a gamble to find a part that you thought you could use but couldn't, and the slightest difference in dimensions of both the inner tube and the brakes can have a significant effect on performance, so don't divert unless you are sure they are the same part.
The next possibility is to get used parts from online auctions. Not only the inner tube and caliper pistons, but also the front fork and calipers are often listed as a whole, and when you make a successful bid, you may find that they are rusted out. You will be lucky if you can get good parts.
When all such means are not available, the recourse is to re-plate the hard chromium plating.
POINT
- Point 1. Even with hard chromium-plated parts, the base material may rust depending on daily care.
- Point 2 - Whenever hard chromium plated parts rust, they need to be repaired.
Who do you ask for the reclamation of hard chromium plating?
Processing at TOYOKOKA Co., Ltd. Hydraulic pistons are ground and finished to the specified dimensions. In many cases, parts for hydraulic equipment and industrial machinery have been used for decades after they were manufactured, and some manufacturers do not keep old parts in stock, so they have to manufacture them after receiving an order. In such cases, the company can remanufacture the original product, minimizing the time it takes to stop production.
Hard chromium-plated pistons and rods are used at construction and production sites around the world, not only in Japan, but also in other parts of the world to transmit hydraulic pressure and power. Unlike motorcycles, which are just for fun, these pistons and rods are used in the harshest of workplaces and are in various states of disrepair. All of them are remanufactured in the best possible way.
Re-plating, in which the rust is removed and the surface of the base material is prepared and plated again, exists in both UNIQLO and decorative chromium plating. However, the re-plating of hard chromium plating is very different from conventional re-plating. This is because it requires equipment that can apply thicker plating and requires higher precision due to the characteristics of the parts.
The external dimensions and roundness of both the inner tube and caliper pistons are very important. It is not acceptable to say that the pistons are made a little thinner because they are heavily rusted. The surface finish of the chromium plating must be machined to remove the rust.
For this reason, there are only a few companies that can re-plate hard chromium plating, and the number of companies that can do this for motorcycle parts is limited. One of them is TOYOKOKA Co., Ltd. in Kurume City, Fukuoka Prefecture.
The company has been around since 1960 and offers a variety of metal surface treatments including hard chromium plating and ion plating. Each of these services is described on their website, but one thing that motorcycle users will appreciate is that they can refurbish their inner tubes and caliper pistons.
TOYOKOKA's technology, which can process cylinders up to a maximum size of 800mm in diameter and 6m in length, has been relied upon by industrial machinery manufacturers and plant companies not only in Japan but also overseas for repairing cylinders of 500-ton class hydraulic excavators.
The cost of rebuilding varies depending on the type of part and the condition of the rust, so it's best to contact us for more information. Also, TOYOKOKA Co., Ltd. is not a motorcycle shop, so they do not disassemble or reassemble the front forks or calipers. If you are not comfortable with the disassembly and assembly process, you can ask the motorcycle shop to re-plate them for you.
Kawasaki KZ900 LTD caliper pistons. The front pistons are shared with the KZ900, but the rear disc calipers are not compatible with the LTD. Many out-of-print motorcycles have been replaced with Lockheed or Brembo calipers because of this.
I asked TOYOKOKA to re-plate the OEM brakes for a repair. TOYOKOKA has a lot of experience in the remanufacturing of iron caliper pistons, and it's hard to tell which pistons were rusted out. Unless the pistons are frequently sold at auction, re-plating is a shortcut to rebuilding them.
POINT
- Point 1 - High precision is required for the regeneration of hard chromium plating.
- Point 2 - Hard chromium-plating of front forks and caliper pistons can be reclaimed by hiring an experienced contractor.
