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2 - Can You Pass the Fork, Please
A motorcycle’s fork assembly seems like a fairly simple mechanism. Basically, it is two shock absorbers in parallel. Unfortunately for those of us with forks which are not correctly working, they are much more complicated than that. Not only do they act as the front suspension of the motorcycle they also steer the bike as well. They are subjected to working loads in numerous planes, and while sliding up and down need to be able to be rotated around an axis for steering. They need to be compliant in the vertical plane to absorb road imperfections yet be totally stiff laterally to maintain steering control. Because of all of the that, if there is any problem in the way they function the sticktion that can cause will be readily apparent to the operator. If you hit a bump in the middle of a corner with sticky forks, it is unpleasant at best and can actually be dangerous, affecting your ability to control the vehicle. There are a number of reasons why forks may not move freely including: • DAMAGE- If the bike has been in an accident or struck by some outside force (like a car backing into the forks in a parking lot) the fork tubes, yoke, or other parts can be can be damaged. The two upper, fixed chrome tubes need to be about as perfectly straight as possible for correct operation, not to mention safety. • WEAR- As parts become worn they might work improperly. Worn dampers might not dampen the movement correctly and allow “pogo-ing” or if the seals or chrome plating on the tubes are not in good condition it can cause fluid leaks. • IMPROPER ASSEMBLY - If things are not put together properly all sorts of things can happen. In this case, when I took my forks apart, I found a copper crush washer which is supposed to be at the bottom of the damper, smashed nearly beyond recognition, inside the bottom of the damper tube and interfering with the spring-and- ball check valve. I also found that the holes in the fork tubes were pointing towards the rear instead of inwards. • BAD or IMPROPER PARTS- I have heard that BMW had a run of top plates on the /5’s that were incorrectly machined causing the fork tubes to be thrown out of alignment when assembled at the factory. I personally have experience with an out-of-spec fender support/fork brace on my /7. • DESIGN and MANUFACTURING - In an article on making the BMW forks work better by Joe Minton in Rider Magazine back around 1985 he stated something like, “If you think that’s a lot of work, you should see what is needed to get Triumph forks to work properly,” so it can always be worse. • ALIGNMENT- If parts do not align properly it is very difficult or impossible to get the forks to operate properly. This is mainly what this article is all about- getting the forks and their related parts in proper alignment. Your forks may be working poorly and you may not even realize it! Try this simple test. Bounce your bike into the compressed position and let it rebound and settle on its own (don’t drop it!). Note the position of the fork legs to the fork tube (what height the bike stopped at). Now pull the bike upwards so the forks are fully extended and release it, allowing it to settle down to where it wishes to stop. In a perfect world the two positions (rested after compression and resting after extension) should be in about the same place on the fork tube. If not, then you have sticktion! Something is removing the fork’s compliance and causing the bike to ride rougher or stiffer than it should. Before proceeding with the checking and adjustment of the fork alignment be sure to eliminate the other possible sources of problems as outlined above. With the forks apart it might be a good time to rebuild the dampers, install new fork springs, clean and lube steering bearings, clean, lube and adjust the wheel bearings if necessary, replace seals, and do other maintenance as well. 
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