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Fork Servicing

The following is offered as suggested methods of servicing the RL250 front forks. As with all mechanical devices under spring tension, there must be concerns for the safety of the mechanic performing the work and for anyone else close by. If you feel uncomfortable undertaking this work, or if you do not possess the necessary mechanical expertise and confidence to safely accomplish the tasks, please allow someone with more experience to complete this servicing. 

Servicing the forks is a necessary part of maintaining the bike and is also an area that is often overlooked. To begin, you might want to review the following:

bulletAre the forks leaking and from where? Forks seals are usually the problem but forks can also leak from seals at the bottom drain screw or from the top cap.
bulletDo the forks hit the stops at the bottom or top of their travel?
bulletWhat is the condition of the chrome plating on the inner fork tube?
bulletDo the inner fork tubes appear to be bent?

If any of the above apply to your bike they should be corrected prior to placing the bike back into service.

bulletLeaking fork seals will require the removal of the leg from the steering stem clamps, the old seal removed, and a new seal installed. You should also determine if the leak was caused by wear of the seal, grit that bypassed the dust seal, or damaged by pitted or flaking chrome on the inner leg.
bulletIf your forks hit the stops then you may have springs that are weakening, the spring spacer is missing, a modification of some sort has been made, or the rider weight, fork oil viscosity, or spring rate are mismatched.
bulletThe condition of the chrome plating in the area wiped by the fork seals will impact how long the seals will last. The chrome plating should be intact and the surface smooth in the area that the seal 'wipes'. If this area is rough or pitted with rust the seal will quickly fail. Replacement of the tube or repair and a re-chrome is the only fix.
bulletA bent fork tube may not smoothly slide within the lower leg or it may  limit the total fork travel. Fork tubes are often straightened and re-used.

The forks should be serviced at least once each season or upon fork seal replacement. I don't particularly see a point in routinely changing the seals. If the plating on the fork tubes is in good condition and the wipers are doing their job, the seals should last several seasons. If you have to replace seals often then you might look into having the fork tubes repaired and re-plated.

Caution: The spring inside each fork tube is under compression. Removing the top cap or the Allen head cap screw from the bottom of the leg will relieve the tension on the spring and can cause injury. Never allow the spring, or anything driven by the spring, to be aimed directly at your face or other part of your body while releasing the tension. The use of eye protection or a full face shield is recommended.

Note 1: Depending upon the reference used, the quantity of fluid in the fork leg is either 236cc or 245cc. The Suzuki RL250 manuals say that the quantity of fluid will impact the firmness of the leg but does not give a range of quantities as would be expected. Since the difference between the two values is less than 4%, I don't see that it is worth a lot of concern. To maintain consistency from servicing to servicing, though, you might settle on one quantity and use it each time.

Note 2: Fluid choices are much easier now than when our bikes were new. The fluid recommendations in the Owner's Manual were for 10W/30 motor oil or Automatic Transmission Fluid (ATF). Today we have fork oils in specific weights designed to operate effectively over a wider temperature range. A 5W or 10W will probably be your best choices. 

Scenario 1: Change fluid only, no disassembly.

Required tools: 22mm open or box end wrench, #1 Phillips screwdriver

It is recommend that you work on one side at a time. There is no need to place the bike on a stand.

If you periodically change the fork oil then there is not much to do. Loosen and remove the top cap with the 22mm wrench being careful to control the release of the spring tension under the cap. For this scenario the fork spring and spacer may be left in place.

Remove the small screw at the bottom of the outer leg with a #1 Philips screwdriver. This screw will be either on the very bottom of the lower leg (earlier forks) or pointed toward the rear (later forks) at the bottom edge of the lower leg. Allow the old fluid to drain into a  suitable and clean container for period of 5-10 minutes. Gently compressing and releasing the forks several times will force additional fluid out.

Note 3: Observe the condition of the drained fluid. If you periodically change the fluid it should be an even color. A dirtier fluid may have lighter or darker streaks through the fluid and, worst case, could even have suspended solids. If the fluid appears an even color, proceed with this Scenario. If the fluid shows streaks or solids, go to Scenario 2 describing fork teardown and cleaning.

Inspect the seal on the small screw removed from the bottom of the lower leg and the top cap o-ring. These are areas that will leak fluid if damaged. Replace the gasket or o-ring as required. Install and tighten the screw.  Fill the leg with new fluid. Install the top cap. Repeat these steps for the other leg.

Before placing the bike back into service check proper functioning of the steering head bearings, tightness of the triple tree pinch bolts, handlebar clamp bolts, front axle torque and lock, and the front brake adjustment.

Scenario 2: Disassemble leg, replace seal

Tools: 22mm open or box end wrench, #1 Phillips screwdriver, 8mm and 6mm Allen wrenches, modified 3/8" drive (or 1/2") 7/8" 12-point socket, several 3/8" (or 1/2") drive extensions, 3/8" (or 1/2") ratchet.

If you have a leaking seal, or if the fluid removed is heavily streaked or has suspended solids, a teardown and cleaning should be accomplished. While it is possible to replace a fork seal without a teardown you do run a real risk of damaging the chrome plating in the vital area where the seal wipes the inner tube and the possibility that pieces of the old seal, or grit dislodged from around the seal, may fall into the lower leg.

The reality is that it is just too easy to accomplish a teardown. Other than a special tool that you can fashion yourself, the only thing to worry over is the correct reassembly.

To begin, place the bike on a center stand or blocks and remove the front wheel and fender. Remove the fork top caps with the 22mm wrench and carefully release the spring tension under the caps. Remove the small drain screw from the bottom of the lower legs (earlier forks) or from the rear of the lower leg at the bottom edge (later forks). Allow the fluid to drain 5-10 minutes into a suitable and clean container. Remove the fork spring spacers, spring guides, and fork springs. Temporarily replace the drain screws and top caps.

The leg is disassembled by removing the large Allen head cap screw from the bottom of the leg with the 8mm Allen wrench. The cap screw is threaded into a cylinder inside the leg. To loosen and remove the cap screw, the top end of the cylinder must be held with the modified socket described below. The inner tube may then be withdrawn from the lower leg, exposing the fork seal.

The special tool required is a modified donor 7/8" 12-point socket. It MUST be a 12-point socket, either 3/8" or 1/2" drive. The wall thickness of the socket must be reduced to a dimension that can be easily inserted inside the inner fork tube. This can be accomplished on a belt sander. Understand that once the socket is modified, the socket will not have the wall strength required to be used in regular service. Also necessary are about 18" of socket extensions and the required drive ratchet.

Loosen the triple tree pinch bolts with the 6mm and 8mm Allen wrenches and slide the legs out. Place the legs on a bench and remove the dust seals and top caps. Using the socket extensions, insert the modified socket inside the inner tube until it engages the top of the cylinder. Loosen the cap screw in the bottom of the leg with the 8mm Allen wrench while holding the cylinder with the modified socket. Once the cap screw has been removed, the inner leg may be withdrawn from the lower leg. Note the positions of the parts for proper reassembly.  

Remove the retaining clips and remove the old fork seals and clean everything in solvent and blow dry. Do not mix the parts from the two legs. Keep the set of parts from each leg separate from the other.

Lubricate the new fork seal and install. Stack the parts on the cylinder, engage the modified socket onto the cylinder and, using the socket extensions, insert the package into the inner fork tube. Insert the inner tube into the lower leg and start the cap screw. Tighten the cap screw while holding tension on the modified socket. Ensure that the gaskets on the drain screws are undamaged. Install and tighten the drain screws. Install the dust seals.

Insert the legs through the clamps in the triple tree. Tighten the upper clamp pinch bolts (6mm Allen wrench) to 20 ft-lb and the lower pinch bolts (8mm Allen wrench) to 15 ft-lb.  Extend the legs out to the stops. Fill each leg with fluid. Temporarily install the top caps without installing the springs. Gently and slowly retract and extend the lower legs by hand to allow the fluid to seek its own levels inside the legs. Remove the top caps. Insert the fork springs, spring guides, spacers, and top caps. Ensure that the top cap o-ring is undamaged. Install the top caps and tighten with the 22mm wrench. 

Before placing the bike back into service check proper functioning of the steering head bearings, tightness of the handlebar clamp bolts, and front brake condition. Install the fender and wheel. Torque the axle nut to 38 ft-lb and lock. Install the brake cable and adjust brake.

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Copyright 2014 Matrix Motor Sport
Last modified: 05/26/14