Lower fork leg anatomy of a /5 BMW motorcycle
A photo diary of the internal components of a /5 BMW motorcycle fork leg.
I plan on rebuilding these forks entirely. Good thing too. The rubber is completely rotted in some spots and it has over 10 years of fork oil sitting in these legs. NASTY stuff.
I snapped these photos partly for the blog, but also for my own memory when it comes time to replace many of these parts and reassemble everything. Please excuse the beat up linoleum floors in my garage.
Feel free to comment or ask any questions. I didn’t plan on this being a ‘How To’ post but more of a photo of the pieces and parts involved in the forks. But the post ends up being a bit of both…
Please note, i removed the entire fork assembly from the frame. The fork rebuild can be done while still attached to the bike. When i go through the reassembly, and mount them to the triple tree, i will have to perform a strict alignment procedure to make sure the forks are installed properly. A misaligned set of forks can cause some harmful results to the rider. I will be sure to post my realignment procedure when the time comes. In the meantime, for reassembly, please refer to Duane Ausherman’s site on fork alignment:
Also, please note that i drained all the fork oil prior to starting this procedure.
I removed the upper chrome fork cap with the BMW tool
I then removed the upper fork bolt that secures the fork leg to the top triple tree and maintains pressure on the internal fork spring. I believe it is a 36mm nut and it can often be secured very tightly. I recommend getting a 38mm socket and a breaker bar for the removal process. The BMW fork wrench is often too small and you can not get the leverage needed to get that nut loose. Before i had a 36mm socket, i remember removing these nuts extremely difficult.
I snapped the following photo so i can remember that the nut had a washer, and the size of the spring spacer. Some models do not have a washer between the nut and the triple tree. And some spring manufactures like Progressive supply a PVC piece of pipe to cut down to size for spring tension. A longer size will equal more tension. I will probably stick with the spacer that the bike has on it. It’s a nice aluminum spacer vs PVC.
The pinch nut for the lower triple tree needs to be removed and then the fork tubes should slide out from the triple tree.
The springs were taken out and the fork legs removed.
You need to grind a flat edge on either side of a 13mm socket. Then install a hex (Allen) wrench in the hole of the socket. Hold the Allen wrench in place and loosen the nut. This will separate the chrome fork tube from the lower fork leg (lower fork slider).
I really need to invest in a good circlip tool. I have bought a few and they never seem to have the correct tension for the precision needed in removing and installing circlips.
The circlip needs to be removed from the bottom of the chrome fork tube.(FigureA)
Then you need to unscrew the lower threaded ring from the base of the fork tube. I used needle nose pliers to fit into the small holes of the threaded ring. (Figure B – though the /5 ring looks different)
Here is a shot of the first stage of my fork disassembled.
I already unscrewed the threaded plug from bottom of the dampener rod.
This photo shows how to remove the upper dampener piston.
Photo of entire fork components… in order of their removal.
Close up of the lower dampener rod’s threaded plug, spring and ball.
Close up photo of the orientation and order of the upper dampener rod and the upper piston for the dampener rod.