FAIL: fork compression - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 21 (permalink) Old 09-22-2014, 09:40 AM Thread Starter
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FAIL: fork compression

Somehow, I've lost all compression adjustment in my fork.
I was starting the Hwy 36 ride, got about 40 miles in, and as the road got tighter and slower, I noticed it was getting harder to hold my line thru the turn, it wanted to run wide. It got real bad, to where it wont hold any kind of lean without feeling like it's going to slip out wide. I ended up turning around and babying it back.

Yesterday, I checked the fork legs for responsiveness. I had the compression set at 8 clicks out. When I hold the brake and shove downwards, the fork makes a squeegee-type of noise, very loud, and the front is very bouncy. Using the ziptie, I measured 50mm of travel that I could get by bouncing the front.
Then I turned the compression knobs all the way closed. It made no difference, I could still bounce the front end, and still got 50mm of travel.
Then I opened the compression all the way up. 16 clicks open. Same thing.

There's no signs of leaking seals. Something must have happened internally. But what?
What would you guys do at this point?

I could take off the caps, remove the springs and check the oil level. I'll change it out anyway.
What more should I be looking for?

John, 2000 RC51 #000100

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post #2 of 21 (permalink) Old 09-22-2014, 09:58 AM
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Garage
Look for metal shavings in the oil... Use a filter when draining the oil, inspect it for foreign objects. Sounds like a piece of crap is stuck in a valve.

-2001 Honda RC51 sp1 " Slightly Modified "
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post #3 of 21 (permalink) Old 09-22-2014, 01:38 PM
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I would personally take apart the forks completely, looking closely every step of the way.

Duckhunter has a good point there.

However it is odd that this happened to both fork legs at the same time


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post #4 of 21 (permalink) Old 09-22-2014, 03:20 PM Thread Starter
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That's what I thought. Both legs fail at the same time?
Problem is, I don't have the shop set-up or any of the special tools.
I'll start with the fork oil, and see how that checks out.

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post #5 of 21 (permalink) Old 09-22-2014, 03:34 PM
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By what I get from your description, since the forks are bouncing, it should be a rebound damping issue.
The spring does it's work but the oil isn't hydraulically controlled to eliminate that bouncing effect.
The compression damping valve is irrelevant I believe.

So it is mandatory for you to take them apart and start looking at the bottom of the inner rebound hydraulic tube (#18) and it's pointy valves on the fork's bottom.



On this part (18) the outer tube has sealing agents with the inner tube and between itself and the fork's inner tube. Check those as well.


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post #6 of 21 (permalink) Old 09-22-2014, 04:59 PM
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At a minimum, you could pull the fork off, up end them to prevent oil loss, and remove the compression valve assembly at the base of the forks to inspect the compression valving.
Beyond that, will require pulling the internals to inspect.

Is your fork action that of insufficient compression damping, where the forks dive excessively under braking or cornering, or are they rebounding too quick?
Neither is a safe condition, but I was curious which action was being affected.

Low speed damping is via a needle valve, while high-speed damping is the shim stack.
If the nut that secures the rebound or compression valve stack loosened and backed out (or completely off) on one or both forks, then you'd have pretty much a greatly reduced or total loss of dampening on the affected circuit (not good ).
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post #7 of 21 (permalink) Old 09-22-2014, 07:27 PM Thread Starter
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The rebound adjusters work as they should. When I close them up, I can shove the front down about 50mm and it takes a couple seconds for the rebound to let the fork legs extend back up. The normal setting for my rebound is right about 8 or 9 clicks out. At that setting, it returns to normal height as it should. Bottom line, rebound and adjusters seem to be working.

The forks really got ugly handling when I started getting into second and third gear turns, lower speeds. That's when it felt like the front tire was completely flat, like it was rolling on the sidewall. (Tire was warm and proper psi) Is that a feeling you would get with lack of compression?

I'm headed down to my garage now to inspect fork oil, and I'll take SubSailors advice to look into the compression valving. I'm assuming that's what I'm calling the adjuster? The unit on the bottom of the fork leg?

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post #8 of 21 (permalink) Old 09-22-2014, 09:53 PM Thread Starter
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The fork oil looked fine in both legs. It was right at 135mm, so exactly the right level. It was a dark color from use, but very clean, no debris or shavings. I dumped it out and strained it to see.
I took one of the compression adjusters off, looked thru the two holes and spun the knob. I couldn't see anything moving up or down, no movement at all. I tried to take the top off of the adjuster, but it's on really tight, and I didn't get it off yet.
Is it ok to remove it? I has four shoulders that look like for a wrench, but I didn't see anything in the manual about servicing it other than replacing the two o-rings on the side??

John, 2000 RC51 #000100

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post #9 of 21 (permalink) Old 09-23-2014, 03:39 AM
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The compression valving is inside the housing.



Use a 19mm wrench to unscrew the valve assembly from the housing.
Don't lose the two o-rings for the housing, there's no part number for them.


Last edited by SubSailor; 09-23-2014 at 01:59 PM.
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post #10 of 21 (permalink) Old 09-23-2014, 08:59 AM Thread Starter
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^Got it, thanks SubSailor.

John, 2000 RC51 #000100

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