changing fork oil Part II Help, I'm baffled

[Dr. Jay]

Hi Gang,

I usually consider myself a halfway decent mechanic but this fork oil change has got me totally baffled at this time. Everything went fine until it was time to reassemble the first side. My factory service manual shows a picture of the cap bolt assembly and emphasizes that the damper adjusting rod must fit in the indent which actually puts the cap bolt assembly threads farther from the threads in the top of the fork tube. It emphasizes that you should turn the damper adjuster in the cap bolt assembly with a screwdriver until it falls and that you will then be able to screw the cap bolt assembly on. In a separate section on assembling the fork it again says that the adjusting rod has to be fit in the semi circular indent in the top of the damper rod and that "if the adjusting rod is not put in this hole the cap bolt assembly will not touch the fork spring." This is counterintuitive, but it's not the biggest problem I'm running into. Regardless of what hole (indent) I put the adjusting rod into, the cap bolt assembly gets about an inch from the spring and the rod runs into something solid deep in the fork. I am not talking about having to index the tip of the rod end with the hole deep in the fork, but rather that after indexing it in that hole it acts as if it is hitting something solid.

I am also having real doubts about my factory service manual  since it specifies that the fork spring length is 14.88 to15.08 and my actual fork springs are 18.88. Additionally, when I drained the fork oil it didn't seem to actually be terribly bad and there was 9 ounces of it. The manual specifies 14.3 ounces, but given the tremendous discrepancy in the manual specification for the spring length I am wondering if even this information is right. I agree with the advice that I have been given to refurbish the whole fork, but right now I am hoping that I can simply get some advice on how much oil to put in and what is going on with the damping rod that is preventing me from even being able to assemble the side I have been working on.
I just want to get it back together and go for a ride tomorrow.  Please help me out with this.

Thanks in Advance!

[andyb]

Would be helpful if you included the fact that you're working on an 87.


That being said:  The damper rod adjuster (the long bit from the fork cap with a D cross section) has to fit in the center of the adjuster in the bottom of the fork.  When you have it right, the fork cap will more easily slide deeper into the fork (closer to the threads).  What can happen is it can get stuck around the outer perimeter, and then a little force to put the cap on bends the crap out of the rod, needless to say things work poorly after this.

According to my Haynes, you're somehow reading the wrong page on the fork specs.  The FJ1100 forks had spring minimum length spec'd as 14.88" when used with a spacer.  The FJ11 without spacer and the FJ1200 through 90 has a listed spec of 19.09" with a service limit of 18.90" (480mm).  So you're likely ok there.

Fork oil capacity for a 1986-87 1200 is listed as 424cc (14.3oz) of SAE10W in US models.  I also see a spec for an oil height of 5.55" (141mm) from the top of the fork tube (with springs out and forks compressed).

Expect that putting the caps on the forks requires a fair bit of shoving to preload the springs and get the threads to catch.  It's a good time to have a helper, and be careful to not put yourself in the line of fire, a fork cap to the face will hurt a fair bit.

[Dr. Jay]

Thanks for the speedy reply. Sorry I forgot to mention that my bike is a 1987. The information about the quantity of oil and the apparent discrepancy between my actual spring length and what the manual said is very helpful.

I probably didn't explain it clearly enough in my first note, but what is really weird is that on installing the cap bolt and damper rod into the leg, the cap bolt lower section (threaded part) will stop approximately 1 inch above the threads in the fork tube as the damper rod hits the top of the damper in the bottom of the fork. If I then wiggle it around a little bit and get it to index with the hole in the damper it will slide in approximately another half-inch but then appears to bump into something solid again before the cap bolt quite contacts the top of the spring. I have tried spinning the damper rod after it apparently is indexed into the damper unit in the hope that there is another hole below the one it first slides into and have repeated this process at least 20 times without being able to eliminate the sensation that the deep end of the damper rod is running into something solid despite the fact that it feels that it is indexed in a hole before it hits this point. Also, assuming I can eventually overcome this problem it is still not clear to me if the cap bolt has to have the damper on the position shown in the manual  (the highest spring preload position) since this will make starting the cap bolt into the threads of the fork tube that much more difficult because of the greater spring compression required. As far as I can tell it appears that the damper rod when it is in the upward position in the cap bolt spins freely relative to the cap bolt and really should not "care" what position the spring preload adjustment is in, but the manual warns in bold print that this is a no no. I know that compressing the spring to get the cap bolt threads started is going to be a bear, so what is the reason that it is supposed to be done this way.

So the really, really big question is, since it appears that I am getting the damper rod started and centered in the damper unit for about a half an inch, what is causing it to stop cold at that point?

I really appreciate the help so far and don't want to be a pest with what is probably a simple problem to someone with FJ 1200 expertise, but I'm still stumped.

[Klavdy]

Matey,
have a look at the actual damper rod itself.
Look at it in cross section.
It is "D" shaped.
There is only one "D" shaped hole in the damper in the bottom of the fork leg.
There are OTHER non "D" shaped holes.
You are sticking it in the wrong hole and yes, there IS something wrong with that.
It is an absolute bastard to get it lined up with the "D" shaped hole.
Just keep trying, it will eventually slide in and you'll know it.

Oh, yeah, try not to lose an eye, the entire assembly can shoot out like a speargun if you're not careful.

[andyb]

Definitely return it to the lowest preload setting at the adjuster before trying to get it in.  Anything past that is just causing more work than is necessary.

If it's stopping cold AND it's in the proper orfice at the bottom, seems that something isn't right and sadly you're going to have to take it apart again.  It does seem to me that you may want to assemble the fork without the spring in it though, just to see how things fit without fighting against the spring tension.

I recall on the 90 it was a right bastard to make things align properly at the bottom, as you're quite blind and have to go by feel.  When you get it right, you'll know it's right, and things should feel correct.

I don't remember how it all works right now, it's been awhile since I was inside an FJ fork.  I wonder if the actual adjustment within the fork needs shifted around a bit though.  If you assemble things without the spring, you should be able to freely adjust the comp/rebound settings with the fork extended as well as compressed though, as the entire assembly slides up and down on the damper rod during normal operation.

[Marsh White]

Andy and Klavdy are spot on.  Just one more tip to add: if you have not taken off the handlebars yet - DO IT!!  I have found that it is about 500 times harder to get that D shaped rod into the center hole with the handlebars on - they block the angle JUST enough to make it a real bitch.

[Dr. Jay]

Thanks again guys I'll be riding tomorrow due to your help. Your knowledge and kindness are greatly appreciated
Based on the information and suggestions that I've gotten, I drained all the oil out of the forks removed the springs and used a strong pencil light to peek down in to the tube to see what I was dealing with. As all of you probably know, and I didn't, the top of the damping unit in the bottom of the fork has a D shaped hole in the center surrounded by additional oval holes which will allow the damping rod to start in but are too slim for it to fully enter. With the springs out it was pretty easy to peek in and properly orient and insert the damping rod into the D shaped hole in the center. It is extremely hard to do so however when you can't see and when the forks are full of oil. Additionally, I noticed that on my particular unit there was a very slight raised burr around the D shaped hole as a result of the damping rod having moved up and down inside it for so long. Furthermore, the slightly tapered end of the damping rod was sharp on its periphery which made it very difficult to get in the D. shaped hole with its raised burr even with the springs out and I was able to see it visually. The sharp edges of the rod and the burr around the hole created an actual barrier so that the rod had to be lifted not slid in. What I did was to very slightly knock the sharp edges off the very tip of the damping rod, and notice the exact orientation of the rod when it was engaged in the hole in a damper. I then reinstalled the spring and without any oil in the forks (which makes it easy to wave the tip of the damping rod around) made sure the orientation of the damping rod was the same as noted when it fit into the D hole and managed to get it to successfully slipped in. Using a small funnel I was able to fill the forks with oil without having to pull the cap bolt far enough out of the forks to disengage the damping rod.

I'm relaying all this minute detail in the hope that it may help somebody else who has a similar problem. Without having been able to see what I was actually trying to accomplish and without deburring the end of the damping rod I don't know if I ever would have been able to get the job done. Most of all, I wouldn't have had a clue as to what I needed to do without the leads that I've gotten from all of you. Many, many thanks.

Dr. Jay

[andyb]