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Old 04-22-2009, 08:45 PM   #1
davidpetersen OP
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F800GS Fork Clacking Noise

There's been lotsa speculation on the causes of F800GS front end clacking. I think I may have found one cause, and I came up with a solution.

I was installing new Ohlins front springs so I had the upper tube caps off, and the old springs removed. I noticed that there's a black plastic inner spring guide, on the upper damper rod, at the top of the tube. It's got 4 ribs on it, and it's about 8" long. Refer to part #3 in the diagram below (these drawings are SIMILAR to the actual parts in my forks, but not identical).

Photo being updated 3-29-10

The spring guide has some free-play on the damper rod. It can move up and down a bit as it guides the spring and keeps it concentric on the rod. The lower position is limited by internal stops, but the upper position is determined by a 13mm jamb-nut that keeps the upper cap affixed to the end of the damper unit. The upper cap is threaded down onto the end of the damper unit, and the jamb-nut keeps the cap from coming loose off the end of the damper unit.

It's difficult to loosen that jamb-nut because you have to grip the damper unit at a point below the spring guide so it doesn't turn when you torque the nut. You'll need a long pair of needle nose pliers that can fit between the coils of spring. Or, you can turn the jamb-nut one way as you turn the upper cap the other way, and they'll break free of each other.

My curiosity was stirred by the free-play of the black spring guide, so I reassembled the guide, the jamb-nut, and the upper cap, without the spring itself, so I could see how things fit. I worked the spring guide back and forth on the damper rod, and lo-and-behold I heard a familiar sound! The spring guide made a clacking noise at the top of it's travel, when it hit the jamb-nut. Maybe I was onto something here.

Here's what the spring guide, damper rod, jamb-nut, and upper tube cap look like, when the spring guide is in the lower position:


And here it is with the spring guide in the highest position:


When the free-play is measured, it's about 1/4":


I have a bunch of prototyping bushings and spacers around the shop, so I picked our a couple 1/4" x 1" diameter thick buna rubber bushings with a 5/16" center hole, just the right size to fit on the upper threaded end of the damper rod. The bushings were smaller in diameter than the 4 fins of the spring guide, so they won't hit the spring.

I threaded the jamb-nut on the end of the damper rod, and slightly compressed the bushings, then threaded the caps in place. I then tightened the jamb nuts up against the bottom side of the caps and checked for clearance between the bushings and the jamb-nuts. Perfect.

I took it all apart, installed the springs into the tubes, fit the rubber bushings and jamb nuts, and top cap in place, and tightened them against each other. No more free-play of the spring guide, it was snug and comfy.

Here's what it looked like:


The rubber bushing can be seen below the jamb-nut and the spring. There's a bit of grease on the bushing, which I found necessary to get my wrench onto the jamb-nut. The rubber bushing cuts down on your available working space, so my usual 13mm wrenches wouldn't fit. I used a grinder to thin out the end of an old 13mm wrench, until it was about 3/32" thick and could slip into the gap between the bushing and the plastic cap, and onto the 13mm nut. I replaced the fork caps and tightened the pinch bolts.

Now for the test ride. Before the new Ohlins springs and my rubber bushing mods, the front end would clack like a barnyard goose everytime I hit a sharp bump. But now the clacking sound is gone. Silencio. Shhhhh.

A hush falls over the crowd... could this be the solution we've been seeking? Well, it worked for me. YMMV.

Update: I had so many requests for these bushings, that I put them on the website. Click here: KlackStoppers

PS. The new Ohlins front springs work great, as does the new rear shock. Money well spent. I got them from Stig Pettersson at PPS.
http://www.bestrestproducts.com/t-links.aspx

Update: The Griz has taken the noise investigation to the next level! Scroll down and read his postings, they shed more light on the possible causes (and fixes).

We're getting there!




.
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davidpetersen screwed with this post 03-29-2010 at 03:47 PM
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Old 04-22-2009, 09:28 PM   #2
Bayner
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Excellent diagnosis and repair Dave!!
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Old 04-22-2009, 09:59 PM   #3
The Griz
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So can this fix be accomplished without removing the forks completely? Can I just remove the fork tube caps and get at these parts? Also, where can I pick up a couple of those bushings? Thanks a ton!
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Old 04-23-2009, 05:03 AM   #4
davidpetersen OP
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You don't need to remove the forks completely. Here's the drill:

1. Bike on centerstand

2. Fit a floor jack under the bash plate, the jack will be used to carry the weight of the front of the bike when the caps are removed. Crank up the jack until the front end is slightly off the ground

3. Loosen handlebar clamps and remove bars

4. I had an overhead rack and ran a couple bungees from the bars to the rack so the bars were kept up and out of the working area

5. Loosen the upper pinch bolts on the fork tubes

6. Unscrew upper fork caps

7. Gently and SLOWLY release the floor jack; as you lower the jack the front end will go down and the ends of the springs and caps will move out of the forks.

8. Continue lowering the jack until the forks are "bottomed out"

9. The ends of the springs, the caps, the threaded damper rod, and the jamb-nut will be exposed.

10. With a 13mm wrench, slip it between the coils of the springs, and try to loosen the nut while you keep the top cap from turning.

11. #10 didn't work for me, so I used a pair of needlenose pliers and slipped them between the springs at the lower end of the black plastic spring guide. I held the rod from turning, while I loosened the jamb-nut.

12. Once the jamb-nut is loose, the end cap spins off the threads at the end of the damper rod.

13. Remove the plastic spring spacer, pull out the spring. Do it slowly and twist it counterclockwise so the oil runs off the coils into the fork body, instead of all over the bike.

14. Black plastic spring guide will be exposed and free to examine.

Note - The damper rod will want to slowly retract down into the fork tube. If this happens it's a real pain to retrieve, so keep an eye on it, or better yet tie a piece of string or ziptie on it so you have a tail you can grab and pull it back up.

15. Without the spring, fit the spring guide on the damper rod, fit the the jamb-nut on the threads, and spin the top cap on the threads until it bottoms out.

16. Finger tighten the jamb-nut against the bottom of the top cap.

17. Observe the up-and-down free play of the spring guide, between the lowest position, and the upper position where it touches the jamb-nut. Listen to the sound it makes when you really whack it upward.

18. Measure the amount of free play between the jamb-nut and the spring guide.

19. Select an appropriate rubber bushing to match the free-play. My bushing was 1/4" thick, 1" diameter, with a 5/16" hole. ** see bottom of page.

20. Take everything apart again, and fit the spring into the tube, along with the spring guide.

21. Slip the rubber bushing onto the end of the damper rod.

22. Fit the jamb-nut and finger tighten it down onto the bushing; you will be compressing the bushing a bit.

23. Fit the top cap to the end of the damper rod, and spin the cap down until it bottoms out. It should not be touching the jamb-nut.

24. Tighten the jamb-nut firmly against the top cap.

25. You may need to modify a 13mm open end wrench, by grinding the sides until it's less than 1/8" thich. Otherwise it's impossible to fit the wrench between the rubber bushing and the top cap.

26. The rubber bushing should be in a very slight compression between the jamb-nut and the spring guide.

27. Elevate the floor jack; as you do the fork springs will retract into the tubes.

28. Lubricate the top cap's rubber o-ring seals with a bit of grease.

29. Press the caps down until they engage the inner threads of the tubes, and tighten the caps to recommended torque settings

30. Tighten the pinch bolts of the triple clamp.

31. Elapsed time: less than an hour.

32. For safety reasons, always remove the floor jack before riding the motorcycle.



** The rubber bushings I used were from a prototyping project, and needed to be modified to fit by cutting off a shoulder. I'll offer these for $7.00 PPD thru my website. They're called the KlackStopper. Click the link to go to the ordering page.

Please don't bust my chops for "selling them" here, instead of the vendor forum. They're being offered as a service to my fellow F8GS riders, not as a moneymaking venture.

Or you could make your own. But whatever you decide, use rubber, not something hard like stacked washers.

.
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davidpetersen screwed with this post 04-24-2009 at 08:29 PM
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Old 04-23-2009, 06:53 AM   #5
itsatdm
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It is easier to take the forks off, imo. My home made "hold the spring down thingy". Depress the spring and slip under the lock nut..

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Old 04-23-2009, 07:11 AM   #6
marc morgan
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Dave:

Way to go. I think that is exactly what it is. I've had that since day one. I guess now , I see that it is not really a problem so if I can live with the rattle, at least I'm not doing any harm to the bike. Thanks.
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Old 04-23-2009, 07:13 AM   #7
davidpetersen OP
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Taking the forks off the bike is easier than removing the top caps?

The spring thingy is a good idea, but it's gotta fit in the same space as the new rubber bushing. That empty space is what allows the black plastic spring guide to move up and down and clack. So the spring thingy may not fit once you've inserted the new rubber bushings.
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Old 04-23-2009, 08:26 AM   #8
The Griz
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Dave,

I'd love to buy 4 of those rubber bushings from you. 2 extra in case I screw something up or they wear out! Let me know if this is possible. Thanks again for this write-up. I was convinced the clack was from the rotors and calipers. But your diagnosis makes a lot more sense.
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Old 04-23-2009, 09:00 AM   #9
sillymike
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Tag for interest!

The GF just brought her new F800GS for servicing and she was complaining about that 'clacking' noise...

Mike.
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Old 04-23-2009, 09:12 AM   #10
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I think I'll try this at the weekend.

Being really lazy I might even try and split a rubber spacer with a sharp blade, push it onto the shaft and use a little blob of super glue to rejoin as once in place its looks like it can't go anywhere and it'll save wrecking a 13mm spanner.
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Old 04-23-2009, 09:45 AM   #11
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Thanks Dave, a great thread to be added to the Index thread.

So this cure is purely for the sake of eliminating this noise and there's no other "issue" with the forks?
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Old 04-23-2009, 09:49 AM   #12
The Griz
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Quote:
Originally Posted by svowles
I think I'll try this at the weekend.

Being really lazy I might even try and split a rubber spacer with a sharp blade, push it onto the shaft and use a little blob of super glue to rejoin as once in place its looks like it can't go anywhere and it'll save wrecking a 13mm spanner.
That's a good idea! Only, how are you going to hold the spring back while you slip the split rubber spacer on?

I'd just go to the hardware store and buy a cheap 13mm open end and sacrifice it. For me it's a small price to pay for silence riding over the bumpies. Especially when I'm riding this beast off-road! That's when the noise rears its ugly head the worst for me.
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Old 04-23-2009, 09:51 AM   #13
The Griz
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Quote:
Originally Posted by Gadget Boy
Thanks Dave, a great thread to be added to the Index thread.

So this cure is purely for the sake of eliminating this noise and there's no other "issue" with the forks?
Yeah, the forks will operate completely normal without this cure. It's just that they'll operate noisily. This is just all about killing the annoying "clack, clack, clack" when driving down the road.
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Old 04-24-2009, 11:13 AM   #14
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Instead of sacrificing an expensive Craftsman 13mm spanner to the grinder, you could get one or a set of these:

http://www.lickbike.com/productpage.asp?PART_NUM_SUB='2402-13'



You'll probably find uses for them later on too.
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Old 04-24-2009, 02:19 PM   #15
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As I reached the apex of my very first flight on my F800,
I had time to think to myself "oh dear, I've really launched her,
I hope I don't bottom out upon landing" (maybe not the exact words)
To my pleasant surprise, she landed nice and level, and very cushy.

It was kind of an accidental flight but kind of not. I found a hidden dirt
road on my way back from camping, with a long line of oversized whoops,
spaced about 20 yards apart. I think it's ridden a lot by four-wheelers.
They were actually dried out pools with a nice big berm in front.
I hit the first few conservatively then they got a little steeper and I got a little braver until finally snapping the throttle in second gear like I was on a CR250.

I swear I was 10 feet in the air if I was an inch.



ok, maybe not. probably 4 or 5 though, and it really handled it well,
with my 185 lbs. + gear and about 20 lbs. of camping gear on the back.

I don't remember hearing a clack.

Also, after careful inspection, my drawers remained unsoiled.
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