Fork Seal Replacement - Honda CRF Twin Chamber Forks

By "Mister Wrench"
 

All that’s needed for this job is a clean work space, some basic and specialized tools, fork oil, seals (dust and oil), seal grease, a bit of knowledge a Thursday evening and your ready to go!

You'll need a few specialized tools like; A cartridge wrench, fork seal driver, and impact gun (electric works for twin chamber application).

There are many different types of procedures for various brands of forks. Please understand this article is only an instruction in concepts. Make sure to always refer to your service manual for details and seek the help of a qualified technician if you are unsure.

Start by counting the number of turns or clicks it takes to seat (clockwise) the rebound adjusting screw and record this number. Then fully loosen the screw! Remove any air bleed 'buttons" from the fork cap if so equipped. Note that oil can come out of the unplugged hole when the fork is inverted so be aware.  Work on one fork at a time. Stickers (off road permits or sponsor type) on the upper case won't align if left and right parts are mixed up during assembly. If you can remove and reinstall your forks you’re almost done.

#1 Damping Rod, Lock Nut and Rebound Adjuster


First loosen the cartridge from the upper case at the top of the fork (this is the outer nut not the inner one) striking the wrench with a hammer a few times. Unscrew the cartridge, slide the upper case down. Invert the fork and allow the oil to drain out into a suitable pan. This will take the most time (30mins or more) so take a break for now... Even after oil stops’ draining from the fork some is left in the cartridge on the backside of the compression valve. Look for the holes in the cartridge at the top. Tip the fork back and forth over the drain container so this oil can come out of the holes in the cartridge.

By hand, loosely screw the upper case onto the cartridge until the o-ring seats. With a "sharp" or "new" smaller (#1) flat blade screw driver begin to pry the wiper seal from the bottom of the upper case. As the wiper seal separates from the case use a larger screw driver to finally push it out.  BE CAREFULL! Don't slip and damage the fork tube or yourself! You should now be able to see the retaining clip that holds in the fork seal. Remove it as required. Invert the fork and loosen the rebound adjuster (with the impact gun). As you compress the fork the damping rod will appear. Hold the lock nut with a wrench and remove the rebound adjuster from the damping rod. Unscrew the cartridge from the upper case. Remove the cartridge assembly from the fork and set it aside.

#2 Left to right- Upper Case, Lower Bushing and Upper Bushing


The rebound adjuster will have a rod also (inside the damping rod). If it is not attached to the adjuster, remove it from the damping rod. You are now ready to separate the fork tube from the upper case. This is done with a "slide hammer" motion holding the fork tube and upper case. Be firm but gentle and use a twisting motion. After a few attempts check to see if the fork seal has started to move past the retainer clip's lan in the upper case. This is a good sign that the fork is coming apart ok so continue until the tube and case separate. STOP if the fork tube and upper case bind or you need to exert too much force! That is a sign that the fork seal or the lower fork bushing is stuck in upper case and the upper bushing is trying to pass through the lower bushing.

Use heat from a propane torch on the upper case in the area where the fork seal and lower bushing are pressed in (see illustration #2 above). Heat to about 300 degrees (enough to sizzle spit) oil around the fork seal should start to bubble. Wait about a minute (careful with the hot parts) then try the "slide hammer" method again. After a few attempts check to see that the fork seal is starting to move. Reheat if required. The upper case should be able to separate from the fork tube now. Caution when using a propane torch and be sure to have adequate ventilation.

#3 Left to right. Top to bottom. The Rebound Adjuster and Rebound Adjuster Rod. The Cartridge. The Upper Case. The Fork Tube with six parts in order.


The only loose piece inside the fork should be the fork spring. In illustration #3 the spring is still inside the fork tube. If there are any other loose parts inside the fork something is very wrong or broken... Seek help! We are now ready to disassemble the parts off the fork tube. Set the adjuster, cartridge, upper case and fork spring aside to continue draining.

#4 Left to right. Wiper, Clip, Fork Seal, Back Up Washer, Lower Bushing and Upper Bushing.


The upper bushing has a slit in it. Use a flat bladed screwdriver (or your finger nails) to open the bushing just enough to remove it off the top of the fork tube. Note the lan that the upper bushing was removed from. It is sharp! Slide the lower bushing upwards off the fork tube, taking care not to damage the inside of the bushing on the sharp lan. Slide off the fork seal back up washer noting its orientation. Some washers are stamped out, "flat" side towards the lower bushing and "soft" side towards the fork seal. NOTE THE ORIENTATION OF THE FORK SEAL! There is a top and bottom side to the fork seal. If the new seal is installed upside down it will leak and you'll be doing this all over again! Slide the fork seal upwards off the fork tube. It may get "hung up" on the sharp lan. Use your thumb to push the seal into the lan then lift the other side of the seal out of the lan. Repeat this on the opposite side of the seal and it will come off. Remove the clip and the wiper seal (use the thumb trick on the wiper to remove it past the sharp lan). Note: The seal back up washer should be flat in about 99% of forks. If it is convex shaped it has most likely been damaged during the separation procedure. Replace it if in question!

#5 New Fork Seals with Seal Grease or Fork Oil applied.


Inspection time. The fork bushings have a Teflon coating on them. The upper bushing is coated on the outside and the lower is coated on the inside. Make sure the coating is intact, not fraid or missing. Replace them if required. Check the fork tube for nicks or dings. These cause sharp edges (like a crater) that can cut the lips of the fork seal. Use very light sand paper (2000 grit) and a flat piece of metal to remove the sharp edges. Wrap the sand paper around the piece of metal and rub it in a circular motion over the nick. You should end up with a smooth dent. You can use scotch brite (red) to add "hone" or "hash" marks to the fork tube. This will help the sealing quality and longevity of your replacement. Carefully chuck the lower part of the tube into a vice. Grasp the scotch brite with both hands around the fork tube. Starting at the top of the tube, use a back and forth twisting action (wringing it's neck) as you slowly move towards the bottom. Thoroughly clean all of the fork components. Brake or contact cleaners work well and evaporate as not to leave any solvents behind. Coat the inside of the new fork seal with clean grease or fork oil. Take a piece of a clean plastic bag big enough to cover the top of the fork tube where the sharp lan is. The plastic will protect the lips of the wiper and fork seals from being damaged by the sharpness when they are reinstalled. This is only required when the seals are installed and not for the clip, back up washer or the bushings.

#6 The assembled fork. Upper Case lowered and ready to add oil.


Reassemble the parts onto the fork tube noting the orientation in which they were removed (illustration #4). Make sure the fork seal goes on in the correct orientation!  By hand grasp the damping rod (illustration #1) and screw the rebound adjusters lock

nut all the way up (clockwise) the damping rod until it bottoms out (runs out of threads). Place the fork spring into the fork tube. Slide the upper case into the fork tube. Place the cartridge assembly into the upper case and fork tube. Slide the upper case upwards and screw the case onto the top of the cartridge until the o-ring seats. Invert the fork taking care that the upper case and fork tube don't fall apart. Look into the hole on the fork tube (illustration #1) that the damping rod came out of. While compressing the fork guide the damping rod through the hole. Install the rebound adjusting rod and the rebound adjuster (make sure the adjuster rod engages the flat sides inside the cartridge and on the rebound adjuster if so equipped). Thread the rebound adjuster onto the damping rod and securely tighten the lock nut against it (you don't want this to come apart). Tighten the rebound adjuster into the fork tube. Use the seal driver to install the lower bushing and the backup washer first. Then drive in the fork seal. Look to see the fork seal is fully seated and the clip lan is visible. Install the clip making sure it is seated in its lan. Using thumb pressure (or a soft hammer) push the wiper seal into the bottom of the upper case. Turn the fork right side up. Unscrew the upper case from the cartridge and slide it down. Tip the fork to around a 45 degree angle and add the proper weight and amount of fork oil. Slide the upper case upwards and screw it onto the top of the cartridge. Use the cartridge wrench to secure the cartridge to the upper case. A few strikes on the wrench with a hammer will tighten it snuggly (don't over tighten it). Screw the rebound adjusting screw in (clockwise) until it seats then loosen it out the recorded number of turns or clicks. Push down firmly on the top of the fork and release pressure quickly several times to check the action of compression and rebound. It should be smooth and consistent in both directions. Clean any remaining grease or oil from the fork tube. Reinstall the fork(s) on the bike, double check all fasteners and enjoy the ride!

Side Notes: Twin chamber forks are like a "shock" inside the fork. The chamber (cartridge) is sealed unless you open the cap. Proper torque on the lower triple clamp pinch bolts is very important. The upper bushing has to pass through this. Over torque can cause "sticksion". Manufacture specs for oil quantities may give minimum and maximum. More oil in the fork helps resist bottoming. Forks build internal pressure over time, while riding, and during transport. Use the air bleed screws (or "buttons") to release this pressure at regular intervals (Make sure to extend the forks before bleeding!).

Special thanks to www.2wheeltimes.com for helping make this article possible. Our next article: "How to Adjust Your Engine Valves".

Roost on!
Mr. Wrench