This artical gives an overview of revalving the front suspension of a typical late model motocross bike having sealed cartridge twin chamber forks. This overview includes compression and rebound valving. In this example, Race Tech Gold valves are installed in the forks of a 2010 Kawasaki KXF450. This example begins with the internal cartridges already removed from the fork tubes.
Revalving may be necessary when the suspension damping adjustments can not be adjusted to achieve desired suspension performance. The reason for this is because a suspension is typically made for a target riding weight as well as intended use. One should always start suspension setup with the appropriate spring rates, but spring setup may not be enough to get proper performance. Additionally, a change in spring rate may have a negative impact on rebound valve performance.
Sending your suspension to a suspension company is an option. Companies such as Factory Connection and Race Tech are capable of dialing the suspension to your liking, but this can be expensive. Of course, having done many revalves myself, I totally understand why. To do the job correctly not only requires the right components, but also careful observation, meticulous attention to detail, use of the correct tools, technical understanding and cleanliness. I am not trying to imply that suspension work is difficult, but neither am I trying to say that it is easy.
The best advice I can give to anyone willing to do their own suspension is this:
1 The cartridges shown have already had the oil drained and all of the parts have been cleaned. The compression valve assemblies have been removed as well. You can see how to remove these parts in other suspension service sections.
In my case, it seems every time I get a new bike, the suspension is no where close to being right. The bike is always way too soft for me. Stiffening the suspension with the clickers helps for landings, but makes the bike unridable (or miserable to ride) on bumps, rollers, turns and such. With this 2010 KXF 450, as well as my previous 2005 Honda CRF 450, respringing the bike for my weight made the high speed rebound ineffective and the compression somewhat harsh. Not being able to get good performance prompted this revalve.
2 Getting to the rebound valves on these forks requires removal of the piston rod from the cartridge cylinder. To faciliate removal of the rod, the threaded sleeve at the rod end must be removed. At this step, the sleeve should come off very easily. Notice also that I am using soft jaws to hold the rod. Never clamp these components between hard or abrasive surfaces.
3 With the nut (sleeve) removed, do not push the rod out of the cylinder yet.
4 The threads on the rod end are likely to be very sharp. Carelessly pushing the rod out of the cylinder could cause the sharp threads to damage the seal in the cylinder. Using a fine grit sand paper, in the range of 300 to 400 grit, sand all around the threads to dull the edges so they are not sharp.
5 Now you should be able to safely and easily push the rod out of the cylinder.
6 The rod must now be clamped in a holder with soft jaws so work on the rebound valve can begin. All that holds the valve assembly in place is a single retaining nut. However, the retaining nut is locked by the manufacturer. The threaded end is usually "peened" or "staked" so the nut can not come off. Because of this, a file must be used to carefully file the threaded end so the nut will unscrew easily. Always file away only as much as needed. Attempt removal of the nut at different stages of filing to see if it will come off. Under no circumstances should you force it. If the nut will not unscrew easily, file some more.
7 Removing the nut. Use a backup wrench as shown to break the initial torque.
8 With the nut removed, there is nothing holding the valve parts in place. The rebound valve assembly includes a shim stack of many thin spring steel washers, a check valve (spring and washer) and the valve body (piston). Holding a screw driver that is smaller in diameter than the rod against the rod end as shown, slide all of the components onto the screw driver. Always remove these parts in this way because order is critical. These components will all get replaced, but it would be wise to retain them in tact should you need to revert back for what ever reason.
About the rebound stack...
9 With the components removed in this way, order is kept and you can explore the components easliy without getting them mixed up. From left to right: Check valve spring, check valve stack, valve body (piston), rebound shims, retaining washer. These parts will not be needed for the revalve. Still, I chose to save them. I used mechanic's wire to hold everything together in the proper order.
10 This is the rod end with the rebound valving components removed. The next step is to prepare for installation of the rebound valve assembly. First, be certain that all parts are clean, as well as the work area and tools. Make sure that all traces of metal filings are removed. Use compressed air to remove all debris and filings from all surfaces, grooves, ports etc.
11 If you purchase a revalve kit as I have done, you should have all of the necessary shims, nuts, valves and documentation needed. Now is the time to organize all of these items. To continue, you need to know your recommended setup, which you should get prior to starting this job. Race Tech (the kit you see here) does an excellent job of providing the needed instructions, parts and settings. When you buy their kits, they provide you with a recommended setting for your riding weight, age and ability. Additionally, they give you a chart of all the shim stack arrangements for your application, so you can intelligently make adjustments from your setting if need be. Of course, the only way to know if a particular setting suits you is to ride. However, the valve setup Race Tech recommends is typically very close to what you would like. For compression damping, for example, I typically find my self two or three steps stiffer than the Race Tech recommended setup on the high speed stack (I am only speaking about forks).
12 After you have read and understand all of the instructions in the revalve kit, carefully lay out all of the appropriate shims in order according to your recommended setting. Careful attention must be given to each shim because they vary slightly in thickness and diameter. Proper shim selection is critical. You would be well advised to have a decent set of calipers to measure the shim thicknesses and diameters.
13 Place all of the valving parts on a screw driver or rod as shown here. In addition to having the correct order, you must also be certain the valve body is facing the correct direction. It is very easy to position the valve incorreclty, so it should be looked at carefully. Something else that should be pointed out is the sealing band on the piston (valve). It is common for the seal to have burred edges which makes installing the rod into the cylinder difficult. These sharp corners (burrs) can be removed by firmly dragging a finger nail around the edges of the seal. You could also use a piece of sand paper (around 200 grit), but you should only be deburring the seal edges, nothing more.
14 When the valve stack is correctly ordered, slide everything onto the piston rod while holding the screw driver (or rod) against it.
15 Carefully look at the stack to insure all of the parts are fitted to the rod correctly. Visually observe whether or not the nut, when installed, will tightly secure the stack against the shoulder on the rod. Sometimes, washers must be added to take up the extra space.
16 Following the recommendations from the valving kit instructions, secure the nut using the appropriate thread locker (usually blue Loctite). Fixing the nut must be done carefully because you have to make sure the check valve plate is correctly positioned when the nut is tight, and you do not want to damage the check valve. When the nut is tight, the check valve plate(s) should move freely between the spring and valve body. The distance of movement is usually very small.
17 To prepare the piston rod for installation into the cartridge, fill the threads on the rod with grease as shown here. This is to prevent damage of the cartridge seal during insertion of the rod. Also, after insuring that the assembly is completely clean, coat the piston seal with suspension oil. The oil used must be the same as the oil to be used in the forks.
18 Gently insert the rod.
19 Thread the lock nut (threaded sleeve) onto the rod as far as it will go. The rebound valving is now complete for one side.
20 Compression valving is very similar to rebound valving. The functional concept is the same, but the controlling action occurs during compression rather than rebound. Most modern sealed cartridge fork compression assemblies on motocross bikes are as seen here or are very similar. Even with suspensions that appear very different, the theory remains the same, for the most part. The assembly seen here consists of the fork cap, accumulator spring, accumulator piston and compression valve.
About the compression stack...
About the accumulator...
21 The compression valve assembly must be secured in a vice or holding fixture using soft jaws. If you have no means of securing the valve assembly in such a way, do not attempt this work. These parts must be treated delicately and having them remain in good condition is critical. The retaining nut holding the valve assembly in tact is fixed in the same way as the rebound valve. Peening must be filed away so the nut can be removed easily and without damage.
22 Once the nut is removed, slide all of the parts onto a screw driver as shown so you can keep them in the correct order. Use mechanic's wire to store the valve assembly in tact in case you need the valve later for whatever reason. Additionally, you can reference the original assembly during the revalve process to aid in understanding the order of the components.
23 From left to right: stopper plate, compression shim stack, compression valve body, check plate, check valve spring and check valve spring retainer.
24 Ready for the valve kit. These parts must be 100% clean.
25 Prepare for the revalve by organizing the parts from the kit, reading all of the instructions and knowing your valve stack settings from the provided documentation included in the kit.
26 Lay out all of the required shims in order. Insure that each selected shim is correct by measuring with calipers. Sizes and thicknesses may not be easily discerned just by looking at them. Looking from the top of the shims seen here, the first set of 6 shims (all the same diameter) constitute the low speed stack. The next small shim after the 6 is the cross over shim. The remaining shims thereafter constitute the high speed stack. In actuality, the high speed stack is the entire stack, but the cross over shim causes a separation that allows customiztion of performance in the slower speeds of suspension travel.
27 This is the new valve stack assembled on a screw driver shaft.
28 Transfer the valve stack from the screw driver to compression assembly rod.
29 The spring retainer bushing, which is the last piece, may not stay on the rod because of the spring. You may have to hold it in place when it is time to install the nut.
30 While installing the retaining nut(with thread locker applied!), be careful to hold the spring and check plate in position. As the nut is being slowly tightened, continually insure that the check plate can move freely up and down on the rod (the stroke is very small). Caution: It is easy to get check plate in a bind.
31 The completed compression valve assembly.
More service information on twin chamber forks HERE.
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