UNDERSTANDING FORK SEAL AND DUST WIPER PERFORMANCE, FAILURE AND MAINTENANCE
What is the most common cause for a fork seal to fail and how can it be prevented?
Let's learn how to care for motorcycle suspension.
A fork or shock seal will leak for a variety of reasons but much of the time the seal fails then leaks because the bike was washed or sat unused for a long period of time. This compromises a thin crucial layer of lubrication either through evaporation or by washing this layer away that the seals need for survival.
Additionally, most washings also leave behind water spots, which is a hard mineral build-up that act like teeth against the lips of the seal.
The cure? – always wipe or blow off any water spots before storing the bike and ALWAYS wipe or spray a suitable lubricant on the lower fork tubes and shock shaft after each washing. Using a clean dry cloth with some suspension fluid on it is best. Avoid solvent based spray lubricants and always protect the brake rotors and brake pads to avoid getting any lubricant on them.
What else can cause a seal to fail?
Other causes may be dirt or debris in the seal or a scratch nick or dent on the tube. Nicks are usually caused from roost that comes from your own front tire or from the roost of the rider in front of you. Nicks have an indentation with a ring around them that protrudes upward. The ring is what causes the lip of a seal to get cut or sliced. In most cases, a nick can be turned down and filled, and with a new seal, will offer trouble free performance for many more years. A dent will seldom cause a seal to get cut or fail, but cause the seal to leak each time the dent is passed under the seal. The best fix for a dent is to replace the tube.
Can dirt or debris in a seal be cleaned out?
A – Yes. Dirt or mud that is built up around the fork can be forced into the seal and trapped between the lips of the seal or between the seal and the wiper. Dirt and such can also build-up between the main seal and dust seal. So yes, cleaning these areas is a good idea, and in many cases can revive a leaking seal but most times it is a temporary fix as damage from abrasive material has been done.
What is a main seal and what is a wiper?
The “wiper” or “dust seal” is the semi-flexible seal that presses into the bottom of the upper fork tube. The wiper can be visibly seen and often has a metal tension spring-ring around the outer parameter. The wiper can be tapped out from the upper tube using a small flat screwdriver, cleaned and lubed and pressed back into place, with the fork on the bike. The wiper attempts to push dirt and debris out of the way, protecting the main seal. The “seal” presses up and into the lower section of the upper tube, and is retained via a press fit and by a large thin clip. The seal cannot be removed or slid down unless the fork is removed from the bike and broken down. If the clip holding the seal fails, the seal and wiper will get blown out and a large amount of fluid will follow.
What are the best seals?
Seals made by NOK and SKF. They are well priced, easy to get, and offer the best performance – an ideal compromise between friction and sealing. Note that in 2012 KTM started shipping most of their bikes with SKF seal sets although NOK seals are readily available for WP. NOK are the OEM seals used by Honda, Kawasaki, Yamaha and Suzuki.
I’ve heard about certain advantages to using a different seal, from the same manufacture, than what my bike originally came with. Is there any truth to this?
A – Yes. There are a host of possible combinations between families of seal sizes that may offer some type of performance change. For example, the 04 YZ 48mm seal is a common upgrade for off-road riders on the 05 to 13 YZs. Seals vary based on how well they seal to how much dynamic friction and static friction (“stiction”) they produce. It’s always a compromise – one for the other. With that, there are some good options, and there are also some things that could not be done. For instance a stronger seal spring replacement. More stiction but longer lasting.
I seem to have chronic seal failures? What should I do?
It’s most likely not the seal. It could be from dry tubes, damaged forks or poorly aligned fork tubes. But a good well maintained seal should last a long time. But a muddy ride can damage a seal in one ride.
We suggest neoprene with grease applied at the wiper. Your seals will thank you.
How often should I change my bushings?
Not as often as you think and not as often as most suspension service shops or magazines tell you to. Dirty fluid and very fast riders are what destroys bushings the fastest. If you can see through the black Teflon coating anywhere on the bushing, it’s time to replace the bushing. Inspect them closely. However, sometimes bushings that pass inspection are replaced so that a new bushing will last the full duration of the next season or service cycle. It is money well spent.
Do I have to replace the dust wipers each time I replace the seal?
No, but it depends on the conditions that you run the bike in. Most applications don’t present an issue. Thick mud, on the other hand can present some problems or create additional wear. But while you are replacing seals the extra cost for a new wiper seems like a good investment.
Do those neoprene wrap around seal savers work?
The simple answer is yes, but not really in the way that you may think. They do offer a shield towards dirt getting tossed directly at the dust wiper, which under certain conditions (such as sand roost) may make a difference. But in general, the fork guard does a good job of protecting the interface of the seal to the tube. Another reason why the neoprene wrap most likely prolongs seal life is that they keep the seal and wiper lubricated. This takes place from the material wicking the fluid and maintaining contact with the tube. Clean and re-grease near the wiper and your fork seals will last considerably longer.
My fork has a build-up of oil down where the tube connects the lug, but replacing the seal did not cure the leak. Why is this?
There is a problem where the joint between the tube and lug (also called a casting) slowly fails. This allows fluid inside the bottom of the fork to escape and pool around the upper lug. If you have this condition, you need to stop riding the bike and get the fork repaired.