by Ed Korn
There are a group of tools that I offer which are intended to make sure the front fork tubes are straight, parallel, and in the same plane, so that the telescopic forks work as smoothly as possible.
When you hit a bump with the front wheel the sliders (the movable part that the front wheel, fender, etc. are attached to) should slide easily up/down the fork tubes, with the oil that is inside them passing through various orifices and converting the bump energy to heat. This keeps the front tire from loosing contact with the ground and also the energy from being passed on to the rest of the bike and your body. The easier the sliders move on the tubes the better this works.
Testing can be done without any of these tools. The best way is with the fork seals removed, but you can get a fair idea of how things are with them in place.
1) The slider is bolted to the damper (the piston like thing inside the fork tube) and needs to be disconnected from it. This is done by removing whatever fastener comes through the bottom of the slider. Sometimes it is under a rubber cap, other times you have to remove the axle to get at it. It can be a pain to remove, and if it turns without coming loose you will need an impact wrench to get it off. All the fork oil will drain out, so be ready.
2) With the bike on the center stand support the front of the engine. Take the front wheel off and put the axle back in the sliders, snugging up any axle nut, pinch bolts, caps, etc. Pay attention to the order that you snug things up. You don"t want to tighten a pinch bolt and then the axle nut, improperly pulling the sliders together.
3) Unscrew the fittings at the top of the forks, remove the springs (they will be coated with oil and will drip), and put the fittings back on. You have to
4) Make sure all brake hoses, cables, etc. are not hitting anything.
5) Grasp the axle and move everything up and then down. If the fork tubes and the sliders are straight, parallel, and in the same plane, and you have removed the seals, the whole assembly will move up freely, and go back down under its own weight. If the seals are in and new, it takes a bit more effort to move it up, and you need to tap the fender to get it to start down, but once moving should pretty much continue on its own. If everything moves easily you are done, if not, you need to find out what is causing the binding.
6) Remove fender, fork brace, etc. one piece at a time and try again. If you find a specific component pulling the sliders out of alignment replace it, straighten it, or shim it.
7) If the sliders are still binding with just the axle in, then the fork tubes need to be dealt with and that is where these tools are used.
The DIAL INDICATOR ADAPTER, used with the dial indicator, will tell you if the tubes are parallel (side to side) to each other. To use it unscrew the cap on the dial indicator that covers the back side of the indicator rod, and screw on the coupling nut in itís place. Make whatever threaded rod length adjustments that are needed, and put it between the two fork tubes. Once just below the triple clamp, and then just above the fender. Wiggle it about so as to get the smallest reading, making sure the threaded rod end is kept pressed against the fork tube. I guess the two readings should be within about .004î (.1 mm)
The ground flat PLATE is used to determine if the tubes are coming out of the lower triple clamp at different angles (front to back). Rest it across both tubes, and see if it will rock like a table with one of the legs too short. Use a feeler gauge under the ìhighî corner to see how non flat it is. Again about .004î (.1mm) is acceptable.
If one of the two checks above showed a problem, use the V-BLOCKS with DIAL INDICATOR HOLDER to check for a bent fork tube. The tube is taken off the bike and rotated on the blocks with the dial indicator used to measure the bow. It is possible to straighten a tube with a hammer and a block of hardwood, but people who don't want to get sued don"t recommend it. New stock and non stock tubes for just about everything are available from me.
If things are not quite correct, and the tubes are only a bit bent (within factory specifications), I loosen the lower triple pinch bolt and upper fork cap/bolt and rotate a leg or push and pull on the legs to lever them about the lower triple clamp. Pretty often that gets things close enough. If not it ís wood, hammer, or part swapping time.
My view is that the closer things are to in line the better the shocks are going to work, though there is no magic number above which they won't. BMW specifies that the tubes themselves be straight within .004 in (.1mm). That is the guideline I used for the suggested permitted out of line numbers above.
This whole thing is a time consuming process, and can easily take up an afternoon.