A Q&A FOR UNDERSTANDING FORK SEAL, DUST WIPER AND

BUSHING 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 either caused from roost

generated from your 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. This ring is what causes the lip of a seal to get

sliced. In most cases a nick can be smoothed down, and with a new seal installed the fork should offer trouble free

performance for many 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 debris 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 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. The proper fit and design of the clip is essential.

The most problematic fork for clip failures are the 48mm WPs.

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, its 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. Soit 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 Is it true that there are certain advantages to using a different seal, from the same manufacture, than what

my bike originally came with?

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 (aka stiction) they produce. Its

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 Its 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 cant 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 pressurized 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

(extension) forces for the first 173mm (about 6.8 inches) of travel. In other words, once pressure in the chamber of

either fork falls below 32PSI, the fork will start to 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 made of wood or

plastic placed between the tire and fender is a good tool to have on-hand when owning a PSF equipped bike.

Obviously, fork seal maintenance is more critical than ever on a PSF. Follow the advice noted earlier.

Additionally, the only two seals that we recommend for the all PSF forks are the SKF-PSF seal kit (ask for the PSF kit)

and the 2013 KX450F main seal, (Kawasaki part number 92049-0737). We do not recommend using the current OEM

CRF450R seals (part numbers 51490-MEN-A31 or 51490-MEN-A51). However, there is an updated Honda seal on the

way. Once tested, we may be able to recommend this as well.

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 destroy bushings the fastest. If you can see through the black carbonized Teflon coating

anywhere on the bushing, its 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 dont 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. The wrap does offer another layer of protection on keeping dirt and debris from entering

the wiper and/or seal with very little to no noticeable friction. The wrap also tends to wick and hold fluid from the tube

and this helps to keep the tube lubricated and free of water spot build-up. Certain conditions may warrant the application

of the wrap more than others. That said, the wrap can also trap and hold dirt so proper maintenance is essential and the

wraps should be replaced as soon as the material begins to breakdown or not hold a proper shape.

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 and once the seal absorbs the WD-40, it will need to be replaced. The solvent bases in contact, carburetor and

brake cleaners will also cause seals and o-rings to swell, but they tend to also clean any lubrication on the tube and that

may cause more seal problems than what it resolves.

Q My fork has a build-up of oil down where the tube connects to 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 cases, its 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 and WRs, 06 to 13 KX450F and 09 to 13 CRF450R. Blowing

this area clear of water and using a water displacement after washing the bike can significantly reduce the likelihood of

the lower leg experiencing this type of failure.

Continued

SMART Performance Inc. 408-406-2089

info@smartperformanceinc.com

ADDITIONAL DETAILS RELATED TO IDEAL FORK PERFORMANCE.

Q What else can I do to assure that my forks are operating as optimal as possible?

A Excess binding or stiction (static friction) can be a big problem and can make the best set of forks feel bad.

Sometimes the problem can be easily fixed, and sometimes you have to work and look much deeper to find the issue.

Here is a comprehensive list and recommended repairs.

Lower tubes are dry A dry lower tube can cause a lot of friction. Lubrication is essential. All seals and dust wipers

should have a bead of grease within them and all lower tubes need to always have a layer of lubricant present on the

tube. The best lubricant is the fluid used in the fork. The worst lubricant is anything with a solvent base in it, such as WD-

40. See earlier Q&A on addressing this matter.

Forks are not parallel Forks do not automatically install and clamp down on the axle as to create a perfect alignment

between the two legs. It is possible for one or both legs to be bowed in or out once everything is locked into place. This is

the result of a given amount of tolerance built into the design so that the bushings dont bind. This tolerance is greatest

when the fork is at full extension. The binding caused from incorrect alignment will become progressively worse as the

fork moves deeper into its stroke. Incorrect alignment can be a big problem. The best method to achieve proper alignment

is to use an alignment tool. The age-old trick of compressing the fork with the right side loose on the axle is better than not

doing anything at all, but it may or may not provide ideal alignment. Once proper alignment is made, a score mark on the

right side of the axle, made next to the hub, will allow an accurate install of the wheel without the use of an alignment tool.

Fork seal and/or wiper is too tight Seals and wipers will create too much friction when they either have too much

clamping force on the lower tube or have an inadequate amount of lubrication present. Too much clamping force can

come from a bad seal design, improper fit or a seal set that has been contaminated with a solvent, (which includes WD-

40). Running an OEM or SKF seal package is best. Avoid low cost seals. Also test the properties of the seal and wiper

install by running the fork leg in and out after each component is installed. A fork leg should move in and out freely and

evenly.

Bushings are too tight Although tolerances on bushings is fairly wide, (some slop is necessary) there are some cases

where bushings can run too tight. A bushing not made to an exact specification can cause a lot of problems. To test for

proper bushing fit, break the fork fully down and run the lower tube in and out of the upper tube with just the top bushing

(called the piston bushing) in place followed by the same test after the lower bushing (called the slider bushing) is in place

(and before the seal or wiper is installed). With the bushings in place, (without the seal and wiper) the fork action should

be super smooth and easy with some slop or play. If not, try a different bushing set. OEM is best. In some cases, some

tubes or bushings have to be machined in order to have a suitable amount of tolerance or play. This is usually only the

case with certain Marzocchi forks and the 05 YZ.

Lower clamp is too tight This is a much bigger problem than many tuners and mechanics realize. When the upper

bushing (called the piston bushing) passes though the upper tube where the lower clamp clamps on the tube, the bushing

can become pinched from the excess clamping force. Do not assume that running the proper torque specification means

an error free install. The best way to validate your bike is to install the upper tube into the clamps without any other fork

component in place, (just the upper tube). Then with the upper fork bushing (the piston bushing) installed on the lower fork

tube, run the lower tube so that the bushing passes through the zone where the clamp makes contact with the upper tube.

Experiment with different torque settings to feel how the bushing or movement is hampered. Because of lateral loads, an

ideal final torque setting may have to be less than the setting that is noted without any binding. For example, if you feel

slight binding at 17 ft. pounds, then your final setting may be best at 15 ft. pounds. The 98 to 03 YZs and most KTMs are

notorious for binding. Additionally, a black ring inside the upper fork tube is also indicative of excess binding caused from

the clamp. Check for this during fork service.

Fork is bent or damaged. - A lower or upper fork tube that is bent (smashed, bowed or oval) may cause binding or a

complete seize. It may be necessary to measure a fork tube on a test rig (using V blocks and a dial indicator) in order to

detect minor damage. Uneven fork bushing wear is indicative of a bent assembly.