Be Careful with Vehicles Stored Outdoors. Why Does Snap Ring Corrosion Cause Inner Tube Point Rust?

To prevent rusting of the front fork inner tube, it is important not to leave the inner tube wet, but the gap between the dust seal and oil seal is often overlooked. In addition to the difficulty of removing water that has penetrated here, the rust that forms on the snap ring used to keep the oil seal in place can affect the inner tube, so special attention should be paid to vehicles stored outdoors where they are exposed to rainwater.

Deterioration of dust seals can cause water infiltration.

An upright fork has the inner tube clamped by the top bridge and under-bracket and the front tire attached to the outer tube. An inverted fork is an opposite: the top bridge and under bracket clamp the outer tube, and the front tire is attached to the end of the inner tube. Due to the structure of the upright fork, rainwater on the inner tube inevitably flows toward the dust seal.

The dust seal is press-fitted into the upper end of the outer tube and can be removed even when assembled to the vehicle body by inserting a flat-blade screwdriver or seal remover around the outer circumference and prying.
Although there is no sign of point rust on the sliding surfaces of the front forks, moisture that has passed through the dust seal has caused rust on the snap ring, turning it reddish brown. Iron dust from the rust is also adhering to the oil seal, and if this gets caught on the lip surface, it can damage it and cause fork oil leaks.

Perhaps one of the most troublesome rust problems that can occur on a motorcycle is rust on the front fork inner tube and gasoline tank. Both can cause significant functional damage, and if the bike is out of print, it can be expensive to arrange parts and costs for repairs.

Among these, inner tube rust is caused by moisture adhering to the hard chrome plating and reaching the inner tube material through invisible cracks. As we have explained several times in relation to rusting of plating, whether it is decorative or hard chrome plating, there are extremely small pores on the plating surface, which appear smooth, and moisture can penetrate through these pores, causing spot rusting.

Since these holes cannot be physically reduced to zero, the best way to prevent rust is to keep plated parts free from moisture or to protect the surface with a special coating chemical. However, for inner tubes that slide against oil seals and dust seals during stroke, even if a coating film is created with chemicals, there is still a concern about durability, so the best course of action is to keep water away from them.

The most troublesome type of rust on the inner tube of upright forks occurs on the outer tube, specifically on the sliding surface from the dust seal to the under bracket, where sharp edges of point rust can damage the lip of the oil seal, causing fork oil leaks. There is also a gradation of rust on sliding parts, and rust tends to occur more easily on the upper part of the fork, where there is less oil film, than on the lower part, where an oil film is easily formed by fork oil.

One of the few exceptions to this is the space between the dust seal and the oil seal that requires attention. Both are press-fitted into the outer tube, but as the lip of the dust seal deteriorates over time, it can allow dust and moisture to enter. A component called a snap ring or circlip fits into a groove in the outer tube and acts as a detent for the oil seal.
It also serves as a guide that when replacing the oil seal, it should be hammered in until the snap ring groove is visible.

In contrast to the lip of the oil seal, which is protected by the dust seal, the dust seal, which is exposed to ultraviolet rays and directly to the wind and rain, inevitably deteriorates at a faster rate. This can affect the snap ring that is attached to the oil seal to prevent it from slipping out.

The moisture that passes through the lip of the dust seal and stays at the snap ring area causes the ring itself to rust, and the rust and moisture cause the inner tube to rust as well. Even if moisture gets inside the dust seal and rusts the snap ring, if the bike is ridden frequently, the front fork stroke will bring the fork oil into contact with the inner tube before the inner tube rusts, making it somewhat effective in terms of rust prevention. However, if the bike is stored outdoors and not ridden for a long period of time, there is a risk that rainwater will continue to stay through the inner tube and cause rust to spread.

The worst possible result could be that the bright red rusted snap ring is buried in the ring groove of the outer tube and cannot be removed, and a rust ring has formed on the inner tube as well.

To protect the inner tube, it is important not to let the snap ring rust

When replacing dust seals and snap rings, the front forks must be removed from the chassis. In addition, when replacing even the oil seal, the removed front fork must be disassembled into the inner and outer tubes. Be sure to loosen the clamp bolt on the top bridge before loosening the top cap on the inner tube.

If the top cap is loosened while the under bracket clamp bolt is tightened, the inner tube will not turn, making the job easier. If the front fork is removed from the chassis first, the inner tube must be secured in some way when the top cap is loosened.

Once the top cap is loosened enough to turn by hand, remove the tire and fender, loosen the under bracket clamp bolt, and pull the front fork out. When replacing the dust seal and snap ring, it is not necessary to disassemble the inner and outer tubes. If the inner tube has point rust or the oil seal is also deteriorated, a full overhaul is required.

The best way to protect snap rings from rust is to prevent moisture from entering through the dust seal lip.
If the moisture is just enough to get in while driving, such as touring in the rain, it may dry out by continuing to ride after the rain has stopped. The problem is leaving it parked and exposed to the rain.

It is difficult to say whether snap rings begin to rust in a few weeks or not until the immobility period is in the order of years because it depends on the storage conditions. However, if you notice spots rusting on the plating of exposed parts after long-term storage, you should be prepared for rusting of the snap ring, even if there is a slight difference.

As long as both the oil seal and the dust seal are made of flexible rubber and have sharp edges at the lips where they contact the inner tube, oil inside the fork will not leak out, and dust and moisture on the inner tube will be scraped off by the dust seal. There is no risk of rust formation on the snap ring. However, as mentioned earlier, if the seal material deteriorates, or if the lip becomes loose due to wear from sliding of the inner tube, and moisture gets into the snap ring, corrosion will occur on the snap ring, leading to rust on the inner tube.

Protecting snap rings from rust = The most effective way to protect inner tubes from rust is to avoid riding in the rain or storing them outdoors. However, not all riders can meet this requirement. Even if you have no choice but to store your bike outdoors, simply covering the bike and avoiding exposure to rain is an effective measure to prevent rust.

If there is no point rust on the sliding parts, does it make sense to bother checking the inside of the dust seal? You may think so. However, by taking the time to do so, you may be able to prevent expensive inner tube replacement and re-plating. If you think about it, it should not be difficult to check the suspension and front forks.