A Q&A FOR UNDERSTANDING FORK SEAL AND DUST WIPER PERFORMANCE, FAILURE AND MAINTENANCE
Q- What is the most common cause for a fork seal to fail and how can it be prevented?
A - A fork or shock seal will leak for a variety of reasons but 90% of the time the seal fails then leaks because the bike was washed. Yes, washed. When you wash a bike you wash away a thin but crucial layer of lubrication that the seal needs to survive. Additionally, most washings also leave behind water spots, which is a hard mineral build-up that act like teeth against the lip(s) 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 such as WD-40 near any seals or dust wipers, and always protect the brake rotors and brake pads to avoid getting any lubricant on them.
Q – What else can cause a seal to fail?
A – Other causes may be dirt or debris in the seal or a nick or dent on the tube. Nicks are usually caused from roost that comes from your own front wheel or from the roost of the rider in front of you. Nicks are like craters on the moon – they 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 smoothed down and with a new seal, may offer trouble free performance for many more years. A dent will seldom cause a seal to get cut or fail, but may 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.
Q – 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 (also called a wiper). So yes, cleaning these areas is a good idea, and in many cases can revive a leaking seal.
Q – What is a main seal and what is a wiper?
A – The “wiper” or “dust wiper” 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.
Q – What are the best seals?
A – Seals made by SKF and NOK. They are well priced, easy to get, and offer the best performance – an ideal compromise between friction and sealing. If your seal is green or has the NOK name on it, it’s a good seal. Note that in 2012 KTM started shipping most of their bikes with SKF seal sets. In 2013 they changed the color of the SKF seal to red. NOK seals are the OEM seals used by Honda, Kawasaki, Yamaha and Suzuki.
Q – Are there seals that should be avoided?
A – Yes and no. Sometimes a seal is basic enough that most of them will get the job done. So…it may just come down to budget and availability. That said, you typically get what you pay for so low budget seals may not be the best choice. The best thing is to find a seal that works for you then find the best source for it.
Q – 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 should not be done.
Q – I seem to have chronic seal failures? What should I do?
A – 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 very long time. For most of us, seal failures should seldom if ever happen.
Q – Where should I get seals and wipers and bushings?
A – The stock (also referred to as “OEM”) Yamaha, Kawasaki, Suzuki, Honda and KTM bushings and seals are of very good quality. You can’t go wrong with these other than the higher than necessary price. Suspension shops typically have better pricing on seals and bushings and will most likely have a better understanding of the options available. You can now also order SKF seals on eBay by going to eBay and searching for “SKF fork seal”.
Q – What about the PSF? What should I do?
A – Starting in 2013 the Honda CRF450R and the Kawasaki KX450F came with a Pneumatic Spring Fork (PSF) which uses a pressured chamber of air to hold the bike up instead of the more traditional metal fork-spring. If the PSF has a fork seal failure, the fork will lose this pressurization and ride lower in the stroke.
Making the matters of a seal failure worse, the PSF uses a counter or balance spring that opposes the compression forces for the first 173mm (about 6.8 inches) of travel. In other words, once pressure in the chamber falls below 32PSI, the fork will suck the front of the bike down. It is also not too uncommon for a PSF equipped bike to have a double seal failure. When this does happen the bike may lose additional pressure after being loaded and strapped down, causing the bike to fall over or come undone from the tie downs. A block of wood or plastic between the tire and fender is a good option when owning a PSF equipped bike.
With that, fork seal maintenance is more critical than ever on a PSF. Follow the advice noted earlier. Additionally, it would be highly advised to run the SKF-PSF fork seal kit, which is an HD version of the standard SKF fork seal kit. If you choose not to run the SKF-PSF kit, then it would be best to only run the 2013 Kawasaki KX450F main seal on both the KX450F and CRF450R, (that is, until the new updated PSF seal from Honda is made available).
Q – How often do I have to replace bushings?
A – 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.
Q – Do I have to replace the dust wipers each time I replace the seal?
A – 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.
Q – Do those neoprene wrap around seal savers work?
A – 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. Additionally, the neoprene wraps tend to trap dirt which leads to a ring of debris that remains at the face of the wiper. However, that doesn’t mean that the wiper or seal will pull the dirt in. The main 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.
Q – Is it true that WD-40 sprayed on a leaking seal may cause the leak to stop?
A – In some cases, yes. WD-40 causes the material in most seals and wipers to swell which creates a bit more clamping force against the tube. This is not a really a fix, but it may save the day or give you a few more hours of ride time. But ideally, WD-40 should not be used on most seals and o-rings. The solvents in contact, carburetor and brake cleaners will also cause seals and o-rings to swell.
Q – 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?
A – There is a problem, that mostly happens with KYB fork tubes, 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. In most case, it’s best to replace the lower assembly than it is to attempt a repair, as the integrity of the joint is always comprised once they come lose or once they are repaired. KYB forks are mostly seen on 98 to 13 YZs, 06 to 13 KX450F and 09 to 13 CRF450R.
Additionally a common reason for leaking at a fork lug is due to using longer than oem bolts to secure your fork guards. The additional length of the bolt will bottom against the chrome tube many times creating a leak.