Fork question

[erod1]

I recently changed my fork seals and oil on my 86 r65. I noticed that the forks are very stiff. Is that normal ? Before I was able to compress the forks with the handle bars. Not now.

[disco51]

What kind of oil did you use?

[erod1]

I used the BMW 75wt fork oil.

[Barry]

Stiffness could be stiction due to fork alignment or too much oil but it would have to be grossly too much.

I'm guessing that was a typo and you meant 7.5wt oil.   75wt would certainly stiffen them up  

[Bob_Roller]

What volume of oil did you put in each fork tube ??

Did you replace the original fork springs with aftermarket replacements, like Progressive springs ?

[Luca]

Well, after a long winded post on your other thread, I saw this one.

Here's a way to sort things out.

With the forks still in the triple trees, remove the large slugs, held in with the C clip, from the top of the forks.  You can remove the springs if you'd like.  They might want to drip oil on nice painted parts.  Try sliding the forks up and down.  If they dont move smoothly, take off the front wheel.  Now try to move each fork up and down separately.  If both move smoothly on their own, then fork alignment is probably your problem.  To fix this, put the wheel back on and play with the triple trees while loosely clamping the upper tubes until things move smoothly, and gradually tighten the clamp bolts down.

If one fork leg does not move smoothly on it's own there is an internal problem and you will have to take it back apart and figure out what is sticking.  Perhaps a piece of the plastic bushing in there jammed something up or the sealing rings on the piston somehow bound.  Or, (if it's possible) you put the piston in wrong.  It should be dropped in through the upper fork leg and then bolted through the bottom.

The only other thing I could think of is that you didn't put the springs back in and both forks are bottomed out... but that would make the bike sit pretty low in the front and the big slugs in the upper tubes would have nothing to keep them pushed up.

[erod1]

I did not replace the springs. I used the BMW oil and I left about one quarter of the bottle. It had ml's listed  on the side of the bottle and I used three quarters of the bottle. Half on each fork. I did not have a measuring cup. It is a quart size.

[Luca]

Best to use a fine graduated beaker or a large syringe to measure fork oil.  The specs are pretty tight on fork fluid levels and the markings on bottles of oil are usually not.

But if you can't compress the forks at all, I doubt the oil level is your problem.

[erod1]

The forks compressed too  much before. One side was leaking oil.

[Luca]

The forks compressed too  much before. One side was leaking oil.

and a leaky fork will get soft as it loses oil.  However, you should always be able to compress the forks by applying the front brake and pushing down/forward on the bars.

If you can't compress the forks at all, you need to isolate the problem.  With the bike on the center stand and a block under the engine remove the top caps from the forks so that they aren't under spring pressure and see if they move freely up and down.  If they dont move together with the wheel still on, take the wheel off and try moving each fork on it's own.  If both move on their own, you have striction caused by poor alignment.  If one will not move at all, you have an internal problem in the fork, either because something bound up inside or (if possible) you put it back together wrong, perhaps by not dropping the piston through the upper fork tube before bolting it to the lower fork slider.

[erod1]

When you say remove the top cap. Do you mean remove the plastic black cap that goes on top of the big nuts on the forks. Also I did not take the forks apart. I only changed the seals.

[Luca]

Sorry Ed, I was thinking of the previous generation's fork design.  Shame on me  [smiley=embarassed.gif]

Nevertheless, you will need to remove the fork spring retaining cap to properly check for striction due to poor alignment.  This is the piece that the spring pushes up against inside the fork.  The black plastic piece is just a cover.

BMW changed their forks in 10/85... so which type you have I'm not sure.  Here are the fiches (but you will need to scroll to the front suspension section 31 and look at the "riser pipe/absorber" picture)

http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51626&rnd=04302013

The earlier one looks like it is threaded and should come out when unscrewed with a large socket, while the later style will need to be depressed and the retaining ring pried out.  If you look at the fiche the caps are different on the two types of forks, so this should help you identify which ones you have.

[bruce_launceston]

I sounds like you may have added too much oil, from memory you only need about 180ml per side.

The other possibility is that when you changed the oil you may have disturbed the remains of the black rubber bush that commonly breaks down and sits in the bottom of the fork leg as sludge. If this has blocked the holes in the damper rod the forks would be stiff.

Did the old oil look black or was it nice and clean?

[Luca]

I sounds like you may have added too much oil, from memory you only need about 180ml per side.

our bikes take 190ml per fork, but starting with 1986 bikes the forks take 300ml of oil, so he should be reasonably close with his .  And since he has a big nut on the spring retainer we can safely assume that BMW didn't use an old set of forks on his bike, if that is even possible (are they the same size?)

[Barry]

(are they the same size?)  

They have larger diameter stanchions which I suppose is one reason for the much bigger oil volume.


Bruce,

I also had a "you have added far too much oil" reponse typed out and ready to post before looking to see it was an 86 model.