As I’m doing a rebuild, I disassembled the handlebars, controls and steering stem along with removing the forks. As the steering is “notchy”, I’m planning on replacing the steering stem bearings and races and I’ll document that in a separate post.
I found a fork rebuild kit at Hucky’s in Section 31 Fork, Shocks, Parts, and picked that up along with some new fork springs. At 97,500 miles and 40 years, the springs have likely given their all. Here’s a list of the parts I used.
|07 31 R kit 005||Front Fork Rebuild Kit|
|31 99 0 000 001||Front Fork Spring, progressive, pair|
Remove Handlebars and Controls
Refer to the general disassemble section and your Haynes manual for more details about how to remove the handle bars. Since I am stripping the bike down to the frame, I had removed the electrics from the frame and the wiring harness earlier so when I removed the headlight and the steering stem, I’d keep the harness attached to it.
Remove Fork Sliders
First, I removed the fork sliders. Remove the rubber plug on the bottom of the slider to expose the 8 mm attached to the plunger. I use the following tool to loosen the nut from the damper, a vice grip holding a 13 mm socket.
As shown below, place the socket on the nut and then insert an allen key into the socket in the bottom of the damper rod. Turn the socket to lossen the nut and remove it.
Next, remove the circular steel bands holding the rubber gators to the fork slider and pull the slider off the fork tube. In the top of the fork tube you will see the fork seals. You can remove these with a seal puller. I find that heating the tubes with a heat gun until it’s hot to the touch makes it easy to pop the seals out of the fork sliders. Be careful not to score the insider surface around the seal.
Here is the disassembled fork sliders with seals (green), sliders, steel rings for the fork gators, the ring under the large fork retaining nut, cap on bottom of fork slider, 8 mm nuts and wave washer.
Disassemble Fork Slider
At the bottom of the fork slider is a large cap nut that seals the bottom of the fork tube. I removed that next by putting the slider in my vice with rubber jaws and using a breaker bar to loosen the nut. Remove the rubber o-ring inside the slider. Here are the parts at the lower end of the fork slider, in order from left to right.
At this point, the fork tubes and internal damper rods are exposed.
Remove Fork Tubes from Steering Stem
To remove the fork tubes, loosen the Allan head pinch bolt on the bottom of the steering stem. I like to insert a large screw driver into the slot and with moderate pressure, spread the clamp a little bit to loosen it, and then twist the fork tube while pulling down on it to slide it out of the steering stem.
Remove Handlebars and Controls
Since I’m going to powder coat the controls, I removed them, but it all you want to do is rebuild the forks, then skip the control removal and just remove the handlebars so you can get access to the chrome covers on top of the fork spring nuts.
I removed the left and right hand control levers. The front brake lever has a switch for the stop light, so remove the rubber boot and then unscrew the wires from the switch. Then unscrew the switch from the control
Then I removed throttle cables and the right side control and disassembled it.
On the left side, I removed the clutch cable from the transmission so I had slack in the cable. I slide the inner cable out of the ferrel as it has a slot cut through one side, and then removed the left side control and disassembled it.
At this point I removed the steering damper rod and the lower friction assembly from the bottom of the lower fork clamp.
This bike had handlebar pull backs. I removed them and the handlebars exposing the chrome forks screw caps.
Now, at the top of the fork tube, remove the chrome cover using the pin wrench in the tool kit. Underneath them you will find a large nut holding the fork springs in the fork tube.
Then, carefully remove the fork spring retaining nuts using the wrench in the tool kit. Since this has fork spring pressure on it, keep your face away from the large nut as it may suddenly get launched if you aren’t careful. Remove the fork springs.
I removed the headlight and then the headlight ears from the steering head. Here is the headlight ears disassembled.
Removing Damper Rod
Turn the fork tube upside down and you will see the snap ring at the bottom of the tube. Use snap ring pliers to remove the clip.
There are two kinds of retaining rings, the one I have and another style that has holes in it that will fit the pin wrench in the tool kit.
Folks have used needle nose pliers spread open to seat the outside of the jaws into the 1/2 circle cut-outs to twist the ring out. I tried that and had no success. My son made a crude tool out of a scrap steel bar with a slot in the middle. I used 3 mm bolts, nuts and washers to create a pin wrench that would fit into the 1/2 circle cut-outs.
And before I got this from my son, I was visiting BMW of Denver and Clem loaned me his tool. This is very clever IMHO.
I removed the top retaining ring using my “scrap steel with 3mm screws” tool.
NOTE: My use of “top” and “bottom” here is from the perspective of looking at the bottom of the fork tube which is the end of the tube facing you as you remove the retaining rings. Of course, when the tubes are mounted in the triple clamps, what I call top and bottom are reversed from the actual top and bottom of the fork tube.
There is a metal ring and then a second retaining ring after that. Rather than adjust the depth of the 3 mm screws in my tool, I used Clem’s on the second retaining ring and it came out immediately. At this point, I pulled the damper rod out the bottom of the fork tube. Below are the parts from outside to inside shown left to right.
Rebuild Damper Rod
Here is the fork rebuild kit I got from Hucky’s. There are new fork tube seals, the white bumper at the bottom of the fork damper, the small metal sealing ring at the top of the fork tube, the big copper ring goes under the large retaining nut at the bottom of the fork slider and the small copper ring goes on the 8 mm threaded stud on the bottom of the damper rod, the six metal rings are piston rings that go in the top of the damper assembly. The large rubber bumper goes in the bottom of the fork slider. Sometimes this has dissolved but in my case it was intact. The plastic bag has small springs that hold a check valve ball bearing in the bottom of the damper rod. I didn’t use them as I left the ball valve alone.
Fork Damper Details
I decided to leave the springs the hold the metering ball in place and just replace the piston rings on the top of the damper.
When I was talking to Clem at BMW of Denver, he loaned me this nifty tool to keep the rings compressed when I reinserted the damper rod into the fork tube. I’ve read that another trick is so use two feeler gauges and then insert the damper rod. The feeler gauges compress the rings so they can slide past the threads in the bottom of the fork tube.
Here’s the tool.
The larger diameter end is conical on the inside so it can be slide up the damper rod from the bottom and will compress the rings as shown below. Note in this picture, the compressor is shown upside down (I always do things backwards at first 🙂 ). The larger diameter part of the compressor should be at the top.
Here is the damper rod with the compressor inserted into the fork tube. You just slide the damper rod through the compressor into the fork tube.
After inserting the damper rod into the fork tube, put the white bumper into the bottom of the fork tube and push it past the threads on the inside of the fork tube.
The two steel threaded rings are identical. The bottom ring has the edge point up so it can hold the metal spacer.
I spun the ring in using a finger and then tightened it using needle nose pliers.
Now, place the metal spacer ring on top of the bottom retaining ring.
Now insert the other retaining ring with the edge pointing downward. I spun it in with my finger and used the needle nose pliers to tighten it so it was below the snap ring groove in the inside of the fork tube.
Finally, I used the snap ring pliers to put the snap ring back into its groove in the bottom of the fork tube.
The small copper washer will go on the threaded portion of the damper shaft when I insert the fork slider onto the fork tube.
Rebuild Fork Slider
But first, it’s time to insert the new fork seals in the fork slider. I heat them up with a heat gun until they are hot to the touch and then pound them in with either a socket or a fork seal tool I use but failed to get a picture of.
I take the large threaded plug that screws into the bottom of the fork slider and insert the black bumper stop so the curved side goes in the bottom of the threaded plug.
Then, I put some Hylomar on the land of the threaded plug and the put the large copper washer on the land.
I mounted the fork tube back in the triple clamp and tightened the Allan bolt. Then I torqued the bottom plug to specifications. Next, I put the wave washer and 10 mm nut on the threaded portion of the damper rod and torqued it to specifications..
Here are the rebuilt and refinished fork tubes.
To refinish the fork sliders, I use Scotch Bite pads (green) and AutoSol aluminum cleaner to get minor scrapes and dirt removed. Next, I use “00” steel wool with AutoSol aluminum cleaner to get the surface clean and starting to shine. I like to use blue paper shop towels to clean off the black residue between applications of AutoSol. This can take a couple of applications to get all the grime out of the crevices in the rough casting. Then, I use AutoSol aluminum polish to get a shine applying it with a blue paper shop towel and finished up with AutoSol Aluminum protective spray and lightly buff it with a clean cloth. These look good as new and I hope work as well.
2017-03-24 Update table of contents; change some picture captions; minor edits.
2020-12-31 Correct size of nut on damper rod: it’s 8 mm and uses a 13 mm socket.