This guide is applicable for these
models of Honda motorcycles
The CB450 K3-K4 uses a one-off fork style that we go a bit more in-depth on right here - Coming Soon
Before beginning this repair you need to remove:
We go by the philosophy of, " If it is already apart, you might as well fix it" over here at Common Motor. When getting into a fork rebuild on the CB450 or CL450 Scrambler, most of the front end needs to be removed to remove the forks so go ahead a remove a few more parts since they will be easy to get to. We recommend cleaning and rebuilding the headlight ears, headlight bucket, front turn signals, triple trees, and steering bearing. Now, most of these are cosmetic parts so you will not be rebuilding all of them, but it is a great time to thoroughly clean and protect them and replace any disintegrating rubber parts. The most important out of these parts is the steering bearing. This likely has not been opened since your motorcycle left the factory. We highly recommend taking the opportunity to at least clean and regrease the ball bearings on the motorcycle or even better, upgrade it to our tapered roller bearings kit. Find out how to do that here:
Step 1: Remove the forks from the triple tree.
Remove the forks by loosening the bolts on the upper and lower triple tree then sliding the forks out. If it sounds easier than it is, you might have rust built up inside the headlight ears and will need to help it out using a hammer and wooden dowel. Do not hammer directly on the fork top cap. Take a moment and inspect the upper triple tree for cracks. It is common for people to over-torque the upper triple trees and crack them. If yours is cracked it MUST be replaced.
Step 2: Break the allen bolt free.
This is easiest with a vice, a heat gun, and a friend. Spend 10-15 minutes with a heat gun heating the lower portion of the fork around the allen bolt. Clamp the fork in the vice horizontally with pieces of wood to protect it. Have your friend compress the fork as much as they can while you crack the allen bolt free on the bottom of the fork. The pressure of compressing the fork helps prevent the dampening rod from just spinning inside the fork as you turn the allen bolt. Having an allen key socket on a ratchet or breaker bar makes this significantly easier. If you are using an allen key, slide a small length of pipe over it to get more leverage.
Step 3: Drain the fork oil.
With the forks removed, unscrew the top cap and move the fork tube up and down drain the oil into an oil catch container. If your top cap is difficult to remove, clamp it back in the lower triple tree to hold it while you break it free. Use a 22mm socket on the top cap and a 19mm wrench on the lock nut and unscrew the top cap from the dampening rod. You can then unscrew the lock nut from the dampening rod and remove the internal spring.
Step 4: Remove the fork tube and seal.
Pull the fork tube and it will come right out of the fork body with the top cap removed. Unscrew the bottom allen bolt the rest of the way and remove the internal dampening rod assembly. Do not forget to remove the copper sealing washer under the allen bolt, it is easy to miss. Remove the snap ring from the fork leg and use a seal puller or large flat head screwdriver to pry out the fork seal. Only pry on the inner diameter of the fork seal so you do not accidentally gouge the surface of the fork leg.
Step 5: Inspect the fork tubes.
Before starting to clean up your fork tubes it's important to take a moment and thoroughly inspect them. For your new seal to function properly your forks need to be free of pitting and heavy wear on the chrome outer fork surface that moves in and out of the fork seal. Again, this only applies to the surface of the fork tube that travels in and out of the seal. Pitting and wear will tear up the new fork seal as well as let fork oil escape so if yours is bad, look for a set of good used condition fork tubes. If your tubes are in great shape where they travel in and out of the seal but the upper half is rusty, your tubes are completely functional and able to be reused. We generally remove the rust found on the upper half of most Honda fork tubes of this era and protect the upper half of the tube against future rust with a little clear coat.
Step 6: Clean everything.
Self-explanatory, right? We clean up the chrome with 0000 steel wool and wash it so it is completely free of grease and grime. If the upper half of the fork tube is rusty, wire wheel the rust off and add a thin coat of clear coat to protect it from future rust. Clean all aluminum pieces and internal pieces so they are grime and dirt-free.
Step 7: Install the new fork seal.
There are two types of seals you can install into your forks, the EZ install brand seals and standard fork seals. Follow the guides below based on what style seal you are installing:
EZ install seals
The EZ install brand seals are great because they can simply be pushed into place. Be sure that the open side of the seal faces down and you place the included aluminum washer on top. These seals are supposed to float in the fork body and will expand when the fork is compressed and under load. With the seal pressed in just until it is underneath the groove, reinstall the snap ring. That's it!
The standard seals are installed by driving the fork seal into the lower body of the fork. To drive the seal into the lower fork body you will need either a tube, pipe, or socket that is slightly smaller than the outer diameter of the seal. If it's too small you will risk damaging the inner seal surface, too large and you will run into the outer fork housing. Slowly tap the standard fork seal into place with your driver. You know you are done when the snap ring groove is right above the seal on all sides. Be careful to not drive the seal further than right below the surface of the snap ring groove.
Step 8: Assemble the fork.
Reinstall the dampening rod into the fork by sliding it into the lower fork leg. Apply a small amount of Hondabond 4 or thread sealant to the allen bolt and thread it through the bottom of the fork leg and into the dampening rod. Do not forget the copper sealing washer. Apply a small amount of fork oil to the inner diameter of the fork seal and slide the fork tube back onto it.
Step 9: Add the fork oil.
In the Honda service manual, they call for premium quality ATF (automatic transmission fluid) but motorcycle fork oils have improved significantly since the '70s. You should now be using only a high-quality motorcycle fork oil in your forks. If you are a rider below 200 lbs. use 10w fork oil and if you are over 200 lbs. use 15w fork oil. Refer below to the exact amount of fork oil you need to add:
CB450 K5 / CL450 K5-K6: 160cc / 5.4 Oz. per leg
CB450 K6-K7: 140cc / 4.7 Oz. per leg
Use a graduated cylinder to make sure you have exactly the right amount.
Step 10: Finishing up the install
Once the forks are full of oil, slide the fork springs over the dampening rod with the tighter (progressive) windings face the top of the fork and screw the locknut on to prevent the dampening rod from sliding down into the fork. Screw the top cap on and tighten it against the lock nut using a 22mm socket and 19mm wrench. Screw the top cap back into the fork tube. Reinstall the headlight bucket, headlight ears, triple tree, and turn signals if you had removed them. Slide the fork back through the dust cover, lower triple tree, headlight ears, and finally into the upper triple tree until the top of the fork tube is even with the top of the upper triple tree. The upper triple trees on these motorcycles are prone to cracking so be sure to follow the torque value below when tightening it.
Torque the upper triple tree bolts to 12 ft-lbs. (16.5 nm)
Torque the lower triple tree bolts to 22-29 ft-lbs. (30-38.5 nm)
Reinstall the front fender, front wheel, front brake cable, and speedometer cable. Re-adjust the front drum brake. When putting your axle holders on, they are directional and need to face a specific way. There is sometimes an arrow pointing to the side that will face the front of your motorcycle, but if not the taller side of the holder will face the front. Be sure to torque the nuts starting with the front nuts first and back nuts on the holder second. Torque specs for them are below:
Torque the front axle holder nuts to 19-23 ft-lbs. (25-31 nm)
Now go enjoy your new suspension!
Parts you might need: