bent forks R75/5

[chasbmw]

I also had this very useful piece of info from Andy B at the UK BMW club on checking forks for stiction, it's nice and logical.


"After years of messing with forks, this is what I do to keep forks working properly through the assembly process. Rather than trying to fix a problem later, I try to correct problems before they become a problem. This works for me.

When I'm putting together a set of forks, I never put the springs or oil in until the last moment. I'll assemble the forks into the yokes with out the brace or axle in place. Put the top nuts on without the springs (don't tiighten). Slide the axle in, leave the wheel off. Put the nut on the axle but don't try to tighten it as there's nothing to tighten to. Grab the axle in the middle and slide the forks up and down, how do they feel? If there is any stiffness, address it now. Try rotating the fork legs (one at a time) to see if there is any better movement in a different spot.

Now that the forks have been slid up and down a few times, tighten the axle pinch bolt. Slide the forks up and down, any change?

Tighten the top nuts, slide the forks up and down, any change?

Tighten the yoke pinch nuts, slide the forks up and down, any change?

Set the fork brace on and thread on the nuts but DON'T tighten them. Slide the forks up and down, any change?

Tighten one side of the fork brace, slide the forks up and down, any change?

Look at the other side of the fork brace, any space between the fork brace and the lower leg? If there is any space or if the brace fits crooked at all, the moment the brace is tightened, the forks WILL bind. The fork brace must be "tuned" to fit both lower legs perfectly. No shims, no nothing,... it must be tuned to fit perfectly.

Each time anything on the forks is assembled or tightened, the forks must be tested. If there is any tightening or stiffness, you have to go back that step and figure out what went wrong and fix it. The forks MUST move freely BEFORE oil or the springs are added."

[barryh]

That's a very good method to align forks and when it's right it's makes you very reluctant to dismantle the front end ever again. You have to eventually and I've been inside my forks since doing it that way but at the very least the stanchions can stay put. No reason to disturb them even if damper valves have to come out.

[jagarra]

Sounds like a very logical and relatively simple method. Love the term tuning the fork brace. When I was in a tech school learning how to fix a certain machine, there were no adjustments, levers had to be "reshaped" to achieve proper operation. I can just visualize how one would approach that with a fork brace, a big vice and pry/ bending / heating equipment.
When I tried my double hoop fork brace for a quick fit one could see the gaps at the mounting points, it could be a real challenge unless you did use shim material of a sort. After all it isn't called a brace for nothing,

[jjwithers]

So to get back on the topic of handling, it appears that a /7 or R100S set of dampener rods can be installed into a /5 set of forks.... right?

[chasbmw]

Do your /5 forks have the threaded collars at the bottom of the fork stanchions?

According to the Fishwick papers you can. Damping will be strongest from forks on a fairing equipped bike. When I went back to stock after my Racetech experiment, I bought a set of RT forks and reused the damper rods.

I had a real issue with damper rod stiction. This was due to the new damper rod wiper rings binding. Snowbum reckons that they are not sized right. I would either follow his advice to reuse old or to machine fork rod to fit later plastic wipers.

[jjwithers]

I think all the chrome fork tubes (Stanchions) have the threaded collars at the bottom.
I stopped replacing the new wiper rings a while back due to the same reasons.
I think I will source a set of late 70's dampeners and see how it goes. (anybody have a set to sell?)
The other question will be which springs to use... I am thinking Progressive springs...

[chasbmw]

Motorworks in the UK sell new damper rods, but I'm not quite sure what that includes, it may be the rod only not including piston.

[Dave Backmarker]

I installed a set of forks from Motobins that are made in Italy. I've had them on my R90S for about two years. They were pretty expensive and are beautifully finished and dead straight. I just checked and it appears Motobins no longer offers forks for airheads.

Dave
1975 R90S
2000 R1100RT

[Duane Ausherman]

I read so much information here that is about half right. Stop trying to take a short cut on alignment methods and hope it works. Just bite the bullet and do the full measurement procedure and then you can be sure.

Several readers here went through the procedure after lazy attempts to take the easy route. It is your bike and your safety, so do as you wish.

I listed many fork damper units on eBay and they didn't sell.
They were made in many versions. The number of holes varies quite a bit as does the damping portion. I don't know the total number of variations that they made. Neither does anyone else.

There is no reason to replace the rings.

One might get lucky with that alignment method above and then again, one might not. The /5 fork brace can and must be turned. The /6 type of stamped out sheet metal can't work correctly. One has to squeeze it to install it. It is then "bent" and will draw together the fork tubes.

I have several sets of used fork tubes that are quite good and are cheap. Some have a minor bend, say .003" and are matched with another tube. The high point of the arc is marked and if one places them both in the same plane, then they work just fine. This is straighter than some of the new fork tubes from BMW.

BMW didn't seem to know that they were using slightly bent tubes and just placed them to have the holes towards each other. There was no good reason to do it that way. It was to reduce the gouging wear from a burr on the holes against the castings. Never saw a single burr and neither did the factory techs that taught the classes.

The risk from using a after market upper brace is that the distance between centers (C to C) isn't exact. The C to C must be the same if you want the forks to work.

The fork design was excellent, but the quality control of the parts was terrible. We never found a single fork that was correctly made and assembled.

[Bamboo812]

I had a real issue with damper rod stiction. This was due to the new damper rod wiper rings binding. Snowbum reckons that they are not sized right. I would either follow his advice to reuse old or to machine fork rod to fit later plastic wipers.

Chas, do you remember what year those plastic wipers were used on?