When I did research on rebuilding the forks on my 88 R100 RT, I found very little information regarding the “Type V” forks on the monoshock RT and RS’s. And, what little I found turned out to have a significant amount of incorrect information. I’m writing this to be used in companion with other information. Clymer indicates the wrong damper rod assembly for the Type V forks. In addition, the exploded views of the forks by both BMW and in the Clymer book are missing an O ring on the damper rod assembly. The BMW fiche indicates only one O ring located on the damper rod; however, there is an O ring on the valve, which is not shown. This O ring on the valve is the same O ring that is on the damper rod, so just double the order. Since I had a hard time trying to figure out what parts to order, I have included a parts list at the end of this article.
First of all, I’m assuming the forks are already off the bike and the sliders have been removed. The fork seals and dust boots (if necessary) should be replaced as well. There are plenty of discussions on how to do these tasks, so I’m going to skip discussions on them. Also, it’s very important to make sure the forks are properly aligned, when they are put back together. Stiction occurs when the fork are not properly aligned, which can be dangerous.
Fork Disassembly
While Clymer recommends disassembling the forks by removing the fork top cap, I found it much easier to remove the circlip on the lower end of the fork. The slight compression of the spring helped. Once the circlip was aligned properly for removal, things just popped up. My springs were not under much compression, but proceeding with some caution is advised. Remove the circlip, spacer ring, valve housing, damper rod, and the fork spring.
The fork top cap is held in place with a snap ring. Next, push down on the fork top cap and remove/pry out the snap ring with a small screw driver. Be very careful not to scratch the inside of the fork tube while removing the snap ring. Make sure the screw driver used does not have sharp edges. One of my fork caps was in rather tightly, and needed to be lightly tapped with a rubber mallet. A broom handle works well to push the top cap up and out from the bottom. If there are some scratches, it’s not the end of the world. My fork caps were installed by the previous owner with silicon sealant due to some scratches. I had to reinstall the top fork caps with silicon sealant. The more expensive solution is to purchase new fork tubes, which will lighten your wallet quite a bit. At about $225 each from BMW, I thought I’d try the silicon sealant approach first. Both fork caps do not leak.
Damper Rod assembly and disassembly
The damper rod must be disassembled to replace the damper spring, and valve spring. Before disassembling the damper rod, it should be measured (FYI: mine were 259 mm), and you should make note of the order of items and their orientation (taking a photo is best). It’s important that the damper rods be the same length when reassembled. The damper piston (called an absorbing piece on the parts fiche) is typically heated with a propane torch to loosen the loctite on it. It’s recommended that the parts be cleaned of oil first to avoid any possible fires. You will need to use a pair of pliers to remove the damper piston; however, heating them up makes them VERY soft, and are easily marred. I purchased new ones. Also, the threads got galled on the first damper piston after two full turns. I ended up cutting off the damper piston and restoring the threads. I recommend putting some anti-seize on the threads.
Assembly of the damper rod is very easy. Just install all the parts in the proper order, and screw on the damper piston with some loctite. Clymer suggests red loctite. My conversations with local experts and the local dealer indicated blue should be sufficient. It’s up to you whether or not you use red or blue. Make sure that both damper rods are the same length as measured before disassembly. Note: If you decide not to rebuild the damper rod, you should be able to replace the two O rings by rolling them up from the bottom.
Inspection
All the parts should be inspected to make sure they are within in proper tolerance ranges. The Clymer Manual seemed pretty thorough in this area, and I have no additional information to add.
Fork Reassembly
Before reassembly, all the parts should be cleaned. The fork top cap with new O ring should be installed with a little a little fork oil. Push the fork cap just far enough past the snap ring location and install the snap ring. The exception here is if you need to install the fork caps with silicon sealant. If that’s the case, then make sure the parts are clean and dry first. Next install the fork spring. Installing the piston with the guide ring is a little tricky. There is a shoulder on the inner side of the fork tube, which the valve housing rests on. The guide ring will get caught on this shoulder and not install properly unless some shims are temporarily installed to allow the guide ring to slide past the shoulder. Shims can easily be made out of 3 x 5 index cards cut to 3 x 4. The thickness of the cards will dictate how many you need to use. Clymer says 3, but I needed 4. Wrap the long side of the cards around the innerside of the fork tube. Then, install the damper rod and the guide ring with a little bit of fork oil. There is a small semi circle notch on the guide ring, and it should be facing down. You need to go slow while installing the damper rod and guide ring to make sure the guide ring stays in its proper location. I found it a little notchy getting it past the shoulder. Once the guide ring is past the shoulder, remove the index cards. I used a flashlight to inspect to make sure the guide ring went in properly.
The valve housing is installed next, then the spacer ring and finally the circlip. You will need to compress the fork spring in order install the circlip. Either get a buddy to compress the spring by pushing down on the damper rod, or you need to get a little creative. I lucked out in this department. I have cabinets above my workbench, and the space between the top of the workbench, and bottom of the cabinets was perfect to compress the fork spring just enough to install the circlip. I compressed the fork between the workbench top and cabinet bottom, which held the fork in place. I was then free to use both hands to install the circlip. Be careful which ever way you do it to protect the threads on the top fork cap. You don’t want to damage these threads while getting the fork back together.
Here’s the part’s list I needed for my rebuild. Since the parts fiche are now readily available on several websites, I have include the fiche and item number on the diagram. Also, since part numbers change, you should double check the part number.
Qty BMW Part # Description .
2 07 11 9 963 073 Fork tube fiche: #23 Gasket Ring (fill bolt on top of fork)
2 31 42 1 454 962 Fork tube fiche: #8 O Ring
2 31 42 1 452 013 Fork tube fiche: #12 Guide Ring
4 31 42 1 452 011 Fork tube fiche: #15 Gasket Ring
2 31 42 1 452 012 Fork tube fiche: #11 Absorbing Piece (damper piston)
2 31 42 1 452 009 Fork tube fiche: #13 Compression Spring
2 31 42 1 232 057 Fork tube fiche: #16 Coil Spring
2 07 11 9 963 041 Fork Slider fiche: #6 Gasket Ring (bolt holding on slider)
2 31 42 2 310 199 Fork Slider fiche: #2 Fork Seal on slider
2 07 11 9 963 037 Fork Slider fiche: #8 Gasket Ring (drain bolt on fork slider)
I used fork springs from progressives, but the BMW part is
2 31 42 1 457 116 Fork tube fiche: #10 Stabilizer (Fork spring)
