3rd gen fork assembly ?

Last night i finally had the time to change my springs (Sonic springs 0,9 kg/mm) and oil (Motul 7,5w) to forks of my my 20 year old black beauty. And it really did need the oils changed, cause the old "oil" looked like muddy black water when poored off from the forks.

Everything went fine, except that the first time I assembled the left fork together I might have tightened the locknut and the cap  a bit too tight and this caused preload adjuster to jam. So I took it off and opened it again and got it loose and after that I started to wonder, how tight should I screw the top cap to the rod ?

I just tightened it hand tight and gave it a little push with a tool and at least the preload adjuster works now. This may be a dumb question, but how is this supposed to do ? Cause if I remember correctly, the amount of thread to be tightened depends on the position of the preload adjuster screw and when you screw the preload adjuster everything changes ?

Or have I got something wrong here ?
Is the locknuts only job to prevent the rod from falling or what ?

And yes I am quite mechanically minded and actually I am an engineer (of a different field), but this really started to puzzle me after I got all back together yesterday and started to drink beer...

Oh yeah...I test drived it in random preload setting (3 lines from the top) and it felt a lot better and firmer than before.

[image: View Post]Xtreme, on 01 May 2012 - 06:24 AM, said:

Cause if I remember correctly, the amount of thread to be tightened depends on the position of the preload adjuster screw and when you screw the preload adjuster everything changes ?

Is the locknuts only job to prevent the rod from falling or what ?
To start with your last question: yes. I back off the locknut and screw on the preload adjuster as far as it goes and then tighten the locknut (hand tight).
The amount of thread you screw into the preload adjuster only influences the position (heigth) of the rebound damper in the fork cilinder assembly. But that doesn't alter rebound damping or anything else as with the correct amount of fork oil it will always be submerged in oil and do what it is supposed to do.

Thanks for fast answering Rosso!

So I think I dont have to tear it apart again then :)
And I would have, cause when something worries/wonders me, I cant stop thinking about it.
So then I guess, it doesnt matter if they are tightened in different "heights" compared to each other either...

Does it make a difference whether the rod is up or down while measuring the oil height ?
I had it down, Dont know if this is the right way to go ?

And what about pumping the fork to remove air...should the rod be also "pumped" up and down or only the cartridge to get the air out and fill all the "holes" ? I think that I did more complete "bleeding" on the other fork pumping picking the rod up and down also and witht he other one I did this only a couple of times but did pump the fork itself a lot...

By the way, my bike is a 1992 (FN) model and the big book claims that it should have a groove on the top of the fork that should be aligned with the top triple...well mine doesnt have one, so I just installed the forks on the same level that they were (thank god I did one at a time), which was about 40mm from the top triple to fork or about 42 mm to fork cap.

Forks might be changed by the previous owner, no way to be sure...

[image: View Post]Xtreme, on 01 May 2012 - 07:02 AM, said:

So then I guess, it doesnt matter if they are tightened in different "heights" compared to each other either... It will only make a negligable dfference in oil height between the two fork legs.

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Does it make a difference whether the rod is up or down while measuring the oil height ?
I had it down, Dont know if this is the right way to go ?
Interesting thought, well maybe only to an engineer :laugh:
I never thought of that but always had the rods down and my guess that when the service manual mentions "compress the fork fully.." this includes the rod to which the rebound damper is attached.
I used to put some rope around the top so I could easily retract them. Now I use one of these very handy €1 tools.
[image: Posted Image]

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should the rod be also "pumped" up and down or only the cartridge to get the air out I am not sure what you mean by "only the cartridge". You mean you try to get the air trapped in the compression valve out by pumping the fork lower? I only "pump" the rebound damper rod to get the air out of the fork cilinder assembly (and this also clears the rebound valve of air). I suppose a tiny amount of air (or old fork oil) can still be trapped inside the compression valve. Then again I don't follow the service manual when it comes to oil height. I think stock is 175mm and I have set it at 130mm.

Maybe the groove is only on the 90-91 model as my 93 doesn't have them either and the forks between the 90-91 and 92-93 model differ.

Thanks again Rosso!

Yeah, I set it stock (178mm) by the book.
Have you noticed improvement after cutting down the air gap that much (whit what springs ? ) ?

I now experience less front end dive while braking. The springs are aftermarket that I bought as a complete set together with a new rear shock.

Just to be sure, I think I'll take the caps off (front jacked up) and make sure that both forks have the same level of oil using the one I know that I bled well as a reference point. Might add a bit of oil too while I'm at it. Although I got mostly rid of the excessive brake dive with the spring change.

Ok, checked the oil levels and those were identical, but I decided to add 30mm oil height while I was at it, so riding now at 150 mm.