Many different fork designs exist across the various models of dirt bikes, new and old alike. The challenge to achieve desired suspension performance in many demanding conditions drives the evolution forward. As suspension improves, new things are learned which in turn yields new designs, yet not every new design is an improvement. This being said, suspension concepts tend to remain basically the same. Given the many different types of forks available, it is important to understand what you have before you attempt service work.
Fork designs, within the scope of performance dirt bikes, are typically the following depending on vintage and bike model.
Below are some excellent videos about how to service various types of forks.
In this video, Scott Gustafson with Dirt Rider Magazine shows how to replace leaky fork seals. The scope of the video extends to replacing fork bushings, how to change fork oil and fork springs replacement.
Replacing seals on inverted sealed cartridge mechanically sprung forks. 19:11 minutes.
Some additional tips by DIRT BIKE RESOURCES:
You can pop the fork tubes apart without the use of heat if you must. Your best option is to follow the advice in the video, however. The heat expands the outer tube making it easier to separate the tubes with minimal risk of damaging the slider bushings. I've done several of these without heat and had no issues.
If you loosen (but not remove) the fork caps before removing the forks from the bike, you'll struggle much less. To do this, loosen only the top triple clamp bolts, then loosen the top cap and inner plug. Loosen them enough that the o-ring seal is not exposed. This is so you will not spill oil out until you are ready to drain the tubes.
Bushing inspection here focuses more on the non coated side of the bushings. However, the coated side is the side that slides and can wear out as well. Every bushing I have replaced was due to wear on the coating side. At some point, the coating can break free from the bushing. Once it begines flaking off, wear is accelerated.
This video by Dirt Rider Magazine shows how to replace fork seals, how to replace fork bushings, how to change fork oil and how to replace the fork springs. Open chamber inverted forks, demonstrated here by Scott Gustafson, do not have sealed cartridges and are typically easier to service than sealed cartridge types. Open chamber inverted forks are found on many 90's models motocross bikes.
Servicing open chamber mechanically sprung inverted forks. 19:40 minutes.
Some additional tips by DIRT BIKE RESOURCES:
Mr. Gustafson explains bushing inspection, but realize the coated part of a bushing often wears out. This coating is an antifriction coating likely containing Teflon or similar material. He indicates the non coated mounting side as the wear surface. This is not to say the mounting side can't wear, as it certainly can after a long period of time. However, the coated side can also wear out and often does before there is a fitment problem on the press fit side. It depends on various factors.
Before sliding the spring in, you can tie a long piece of mechanics wire onto the rod end. This way, you can easily pull the rod up through the spring.
You can pop the fork tubes apart without the use of heat if you must. Your best option is to follow the advice in the video, however. The heat expands the outer tube making it easier to separate the tubes with minimal risk of damaging the slider bushings.
Be careful not to over tighten the fork top caps. This can make removal a problem next time.
This video shows how to service conventional forks from a CBR600. It is an excellent example of conventional forks found on many older full size dirt bikes. Every bike model has potential differences, so you should always refer to the appropriate service manual. The service procedures demonstrated here by James Wright-Roberts show you how to replace fork seals, how to replace fork bushings, how to change fork oil and how to replace the fork springs.
How to service conventional forks. 34:56 minutes.
This video by Rocky Mountain ATV shows how to replace fork seals, fork bushings and fork oil on the damping side where there is no spring. The SFF forks serviced here are the Showa SFF used on some Suzuki models.
How to service the SFF damper side. 12:11 minutes.
This video by Rocky Mountain ATV shows how to replace fork seals, fork bushings, spring and fork oil on the spring side. There is no damping function in this spring side fork tube. The SFF forks serviced here are the Showa SFF used on some Suzuki models.
How to service the SFF spring side. 7:57 minutes.
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