How to adjust stock 89/90 (maybe 91-93) forks ? No owners manual

[capitanoinsano]

Hello
I don't have an owners manual for my 89.  I know what to turn to adjust preload and damping, but it is not obvious what the positions are.   I am thinking that if you line up the red dots  (outer ring, to preload ring) that the lowest setting is when the red dots line up (slots with red).  If so, is CW more preload?  For the damping is the first position after the damping screw red dot passes (CW) the outer ring red dot?  If so, is clockwise more damping.  Not sure why I've never adjusted these.  I have progressive suspension springs up front (not that it matters).

[ren-dog]

I don't have an owners manual for my 89. 

Maybe this Yamaha site can provide you with an owners handbook.
Cheers

[pdxfj]

The outer ring has three marks, each is a different width.  The thicker the line the more pre-load/damping.

The inner ring with the dash adjusts the pre-load.  Line up with the larger dash on the outer ring.

The piece inside the inner ring that looks to take a flat blade screwdriver and has the small dot on it adjusts the damping.  Again moving it to line up with the dashes on the outer ring gives more or less damping.  Move it around and you'll feel where it wants to stop for each adjustment. 

You can't hurt anything by moving the adjustments around.  Sit on the bike adjust them to the minimum level, grab the front brake and work the forks.  Then set to the max level, and work the forks again.  You'll feel the difference.  Fiddle with the adjustments to get a feel for what they do.

[andyb]

As a note, the preload takes a big screwdriver and a fair bit of muscle to set higher.  You push into the fork quite hard and rotate it.  There's 3 settings, and if memory serves you can't go past them, you have to go 1-2-3 or 3-2-1, you can't go from 3-1 or 1-3.

The damping adjustment can go around and around, and requires very little force to set.  Just experiment with it in the garage and you'll see where the settings are.  If they all feel about the same, odds are you should drain/flush/refill the forks, and it's a good bet that you should just tear it apart and stick new seals in while you're there. 

My 90's front end is stock, and I run both as hard as they go, with stock springs.  Fork oil is 15w (stock was 10w) and my airgap/oil height/oil volume is at the stock settings.  Works just fine for the street, with decent tires I can drag the centerstand/pipe at will with pretty good feel from the front end.  If this was to be used for more sporting riding or trackdays or such, I'd definitely consider modifying things for better control.  Most street riders will be likely quite happy with the front end set like this, and I'd imagine that a scratcher would probably want a different bike in the first place.

As far as changing the feel of the front end, far and away the biggest change you can make is to the tire.  Different tires have different profiles, and it makes a world of difference to how it feels.  A rounder profile tire such as the Avon will be a little nervous when leaned over, but dead stable and true in a straight line.  A more triangular profile tire will feel slightly unsettled in straight lines, and be dead stable when leaned over.  Choose accordingly.

Before writing off the stock parts (of any bike!), make sure they actually are working the way they were intended to.  Fork seals, dust caps, some oil, and an afternoon spent dinking about in the garage can absolutely transform the handling of the bike depending on what you started out with.

[threejagsteve]

...an afternoon spent dinking about in the garage can absolutely transform the handling of the bike depending on what you started out with.

Note that Andy said dinking not drinking.
An afternoon spent drinking in the garage, and it might take a week to undo what had seemed like a good idea at the time!

[SlowOldGuy]

One thing to consider about the damping adjustment. 

If someone busted the "damper rod locating screw" (located at the bottom of the fork, it looks like a second fork oil drain screw) during a fork rebuild, then the marks for damping may not line up correctly.

You should still be able to feel the three ball bearing detent positions, but you won't know the absolute position.

DavidR.

[capitanoinsano]

Thanks for the help.  I can use an M12 Allen tool to adjust preload, have done that.  But the damping adjustment still has me confused.  On the left fork I can line up the red dot on the flat blade screwdriver damping adjuster so that the dot reaches a detent on each of the 3 settings.  But on the right fork the detents for the damping adjustment do not line up with the detents.  So I checked a spare set of forks and found the right fork on that set was the same way.  Does the right fork wind up with the dot pointing opposite the desired detent?   My forks were apart once, but pretty sure they were put back together right.  Seems odd that my spare right fork would be the same way (red dot doesn't land on detent pointing at a hash mark on outer fork tube ring

So I can set preload and damping on left fork with confidence, and preload on right fork.  I have no confidence in what my damping setting is on the right fork.

[capitanoinsano]

I may see the problem.  I looked at the shop manual and on the 89/90 it looks like the damping adjuster is connected to a bar (rectangular cross section) rather than a round rod.  This must be so that it can turn something in the damping rod assembly.  So it would be easy for someone to get this adjusting rod 180 out of position, and it may work fine either way.  But it means the dot on the wrong side of the flat blade screwdriver adjuster now (for damping).

Does this make sense?

[andyb]

The damper bar is a D shaped crosssection if I recall right.  Only goes one way in, though can be jammed sideways and made to fit but not work.

The Haynes manual has a good description of how the adjustments look, because they really don't make a lot of sense until you've seen inside and understand how they work.  They almost assuredly won't match what you may think they should.

Easier answer, can you post a picture of your forks with the caps off?  Easy to tell you where you're at that way.

[capitanoinsano]

I'll try to get a pic, but not sure how to upload.  But the red dot on the damper adjust thing (with slotted head) does not reach a detent position with the red dot pointing at any of the hashmarks.  If the red dot were 180 reversed (across the slot), it would face a notch at every detent position.  That leads me to believe that something is reversed.  I have a spare right fork (that is the same way) also.  I will try playing with it and see if the damping seems be related to the what the setting would be if the red dot were 180 reversed.  Maybe the piece that the d-shaped shaft goes into is reversed?   The mechanism feels to be working correctly, just like the left.  You can hear the clicks at detents also.

[capitanoinsano]

I think I've figured out the problem, and I bet half the forks out there have the same problem (or more).  There is a screw in the lower leg that must pass through a part of the damping rod for the damping adjuster to be aligned right.  I have rebuilt 1 set of FJ1200 forks and caught myself not lining up the screw with the hole in the damping rod.  I finally got that set right.  My present FJ1200 has progressive fork springs.  I could not install the caps due to the high force required so I let a shop put the springs in and do the seals while they were in there.  They had better equipment for doing that and the price was low as it was winter.  I think they got the left fork aligned right but not the right.  The Clymer manual states that if the screw is not aligned properly, the damping adjustment won't work.  I may be able to just remove that fork, loosen the cap part way to relieve some spring tension, and turn the screw while holding the leg still until I see the hole line up.  Then put the alignment screw in correctly.  The alignment screw is near the drain screw, low on the fork leg.

I checked out another guy's fj1200 forks and they were both wrong.  The fork dust covers looked new, so I'm thinking whoever did those, did them wrong too.

[SlowOldGuy]

Sounds like I had the correct guess earlier.  You should be able to correct the alignment of the damper rod as long as they didn't bend or break the locating screw.

If an impact wrench is used to break the damper rod allen bolt loose when the locating bolt is still installed, it can bend or break the locating bolt.  You can still get it lined back up correctly, but you will need to hold the damper rod in the correct position while you're tightening the allen bolt.

Even if the rod is mis-aligned, the damping will still work.  You just won't be able to tell what you're setting the damping to.

DavidR.

[Shaun]

I had the same issue with my forks, apparently somebody had been inside and actually installed one part upside down, not good the piece was jammed into the bottom of the fork leg. The other thing I noticed when I took the forks apart to rebuild them was that they had missed the proper location of the damper rod. The rod was not in the matching D shaped slot it was located in one of the passages instead. And yup the locating screws at the bottom were bent, so multiple things to look out for to get them together right. Once I had gone through the stock forks carefully the front end was a whole different beast, it used to feel like a wheel barrow that was over full and now it is a pleasure and hangs on in corners just fine. I also tried a variant on fork oil it is a blend of the shelf 10-15w. Apparently as the weather and forks warm up the fork oil changes viscosity kind of like engine oil, seemed okay this summer and fall always felt good and consistant.

Just some things I have experienced.
Shaun

[capitanoinsano]

 The damping screw moves smoothly and hits detents, so I probably don't have as bad a situation as you did (upside down part).  But I probably have the alignment screw not installed right.  I called the guy at the shop who did it, and he will take care of it.  He is actually a well known local expert and setting up competition dirt bike suspensions.  How ironic is that?  I have a spare set for parts.  Or I think if I bought the gold valve cartridge emulators the hole mess is removed right? 

[capitanoinsano]

OK! Now I think I really figured it out...really, I hope.  In order for the alignment of the outer hash marks on the cap to mean anything to the damping adjustment the middle adjustment (medium sized hash mark), must be facing forward (toward front wheel).  My right fork is not installed that way, it is 180 out, so no hashmarks are pointing forward.  If I were to grab the tube and rotate it 180 in the bike on the right fork, the hashmarks would line up right.

It didn't make sense to me that a suspension expert like this guy would make a mistake, but everyone's human.  So he probably did not make any mistake. 

If forks are off the bike to see if the stuff is aligned right you have to put the fork in front of you with the fork brace thing pointing the right way, rotate the tube so that position 2 is pointing forward, then see how things line up, because that's the way it's supposed to be installed in the bike (THIS IS A THEORY though, I'm working without an owner's manual and the Clymer book doesn't say squat.