Posted 26 May 2006 - 06:32 pm
I'll give it a go. I've done this on a TDM900, but not on an 850 so some of the details may be slightly different. I've also checked the Haynes manual, but this is well known as the "Haynes book of Lies", ie its not always correct.
I'm assuming you've got the forks off the bike.
You will need just over 1L of fork oil, so you'll probably have to buy 1.5L. The standard oil is 10W, buy some good stuff like Castrol Synthetic.
You'll also need a ruler.
1. Slacken off the preload adjuster, ie fully out.
2. Undo and take off the cap bolt - the big nut at the top of the fork tube. The damper adjuster rod (thin rod) comes off at the same time.
3. Remove whatever washers and spacers you find, followed by the spring. I think the 850 just has a spring seat (like a big washer) and the spring. Lay them out on clean newspaper so you know what goes where, and to keep them clean.
4. To drain the oil tip the forks upside down and a lot of the oil will drain out. Pump the forks 10-20 times to get as much oil out as possible. If possible, leave them for an hour or so, upside down, to drain.
5. Before you go any further look at the shape of the damper adjuster rod thats connected to the cap bolt. On the 900 its "D" shaped. Now compress the forks and look inside the fork tube. Deep down is the damper rod, with a similar "D" shape hole in the middle. When you come to reassemble the forks the adjuster rod has to slot into this hole. Mark on the outside of the fork slider the position of the flat part of the "D" so you've got an idea how to align them.
6. Pour about 400ml of oil into the fork, and then pump it up and down 10 times so you get oil past the damper.
7. Compress the fork tube fully, and slowly pour in more oil. Use the ruler to measure the distance between the top of the oil level, and the top of the fork. When you get to 130mm stop. Pump the fork a few more times - the oil level may drop so you'll have to add a little more to bring it up to 130mm (with the fork fully compressed). You will find bubbles in the oil, in an ideal world you would let them disappear before doing the final measurement.
8. Extend the fork tube fully, then put in the spring and spring seat (+any washers etc). If the spring has somes coils closer wound at one end (I don't think the 850 has this) then these go at the top.
9. Take the cap bolt and adjuster rod. You're now going to refit the cap bolt, but to do this you've got to align the adjuster rod into the damper rod. Try to poke the adjuster rod into the hole in the damper rod (you can't see it now cos its covered in oil). It can be tricky but you've got to get this right. Try turning the damping adjustment screw - does it feel right, or is it too loose? If its too loose then you haven't got the rod into the hole so try again.
10. Screw on the cap bolt. This can be tricky. I usually hold the slider (lower part of the forks) in a vice, fully extend the forks, and use a large socket/rachet to push down on the cap bolt against the spring pressure until you can tighten it. Correct torque setting is 24Nm (not especially tight for such a big nut).
