RaceTech Rebuid Front Suspension on 2007 F800ST - BMW F800 Riders Forum & Registry



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  1. #1
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    After taking my F800ST to a track day to learn more about high speed cornering (video: https://www.youtube.com/watch?v=d0R2bVl5OaU), I am beginning to realize just how important a proper suspension setup is to safe and enjoyable riding. The suspension on my bike was 100% original, that is to say 13 years old and setup for someone lighter than me. An experienced rider sat on the bike and confirmed that for my weight the forks were too soft and probably needed an overhaul. My experience is detailed below, and after the overhaul I can say the bike rides MUCH more confidently and feels better planted on the ground. Before the rebuild the front felt mushy, sharply reacted to high speed bumps and dove considerably under braking. But now it is like having a new motorcycle. Maybe time to upgrade the rear spring???

    I started at the Race Tech website, put in my bike information and ran their suspension calculator. I found that I definitely needed stiffer springs and that gold emulators could really improve resistance to nose dive when braking. So I ordered a pair of springs, gold emulators and two quarts of 15 weight fork oil. $330 USD

    Two days after the springs arrived, the right fork seal started leaking on the bike.... I think the bike knew she needed some tender loving care.

    The BMW parts were $220 USD for fork seals, dust caps and all seals and bushings for a fork rebuild. I found all the instructions I needed from Race Tech, YouTube and this forum. The only hard part was removing the C-clips that hold the cap plugs in the top of the forks. The trick I found was to place a 2 mm flat screwdriver in the groove between the ends of the C clip and rotate 90 to push the cap down and take the pressure off the clip. With the pressure off the clip it can be rotated in the groove. I cut a strip of 0.001 inch thick brass shim stock about 3 mm wide and placed it in the C-clip groove. Then I rotated the clip using another screw driver so that the other end of the clip was pushed into the loop of metal. Once the end of the clip was in the loop it could be easily pulled out. I couldn't get any of my picks to fish out the end of the clip.

    The fork rebuild went very well. The damper rod (tube) bolts came out easily, however they should be removed before you remove the springs. An impact driver will help but you need an extra long hex key adapter to reach the bolt. Drilling the damper rod per the Race Tech instructions was also easy due to the rod being made of relatively soft steel. A good vise, drill press, cutting oil and sharp bits are all that are needed. The Race Tech Gold Emulators come with a code you use on their website to get the full setup details for rebuilding the forks. It is a one-time use only code and specific for your bike, weight and riding style. The details include preload, oil level and emulator setup.

    The new RT springs are shorter than the original so longer spacers were required. The RT springs came with about 600mm of aluminum tubing to use for the new spacers. I cut them to length on a miter saw equipped with a metal cutting blade. I also measured the spring rates of the old and new springs. My new springs were about 20% stiffer than the originals.

    Driving the new fork seals home requires a proper tool. I found the last 2 mm of travel to require a couple of strong blows from a heavy hammer. I 3D printed a fork seal tool that allowed a piece of PVC pipe as a hammer extension.

    Setting the fork oil level was also made a lot easier by using a tube to suck out excess oil. Just insert the tube down to the correct height and suck out the extra oil until you get bubbles. I have a hand vacuum pump for bleeding brakes, but you can also use a siphon. The fork must be collapsed, the emulators inserted and the spring removed for setting the oil level. If you still manage to bottom out the suspension on those big dips, add more oil in 10mm increments until fixed.

    I cleaned all the parts thoroughly before reassembly, but got them both done in one evening. Luckily my steering head bearings and damper were still smooth and ready for more action. Reinstallation took about an hour to put on the forks, wheel, fender, calipers and fairings.

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    Last edited by Timskloss; 09-23-20 at 09:11 AM.

  2. Thanks Runmyownlife, Daboo, Buzzz, Willy, Kukopia and 1 others thanked for this post
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  4. #2
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    Fantastic post! I really appreciate the detail. Many will benefit from your efforts. Thank you.

    A few questions....

    1) I can't depress the right side fork cap. There is too much resistance. Did you remove the caps with the forks on the bike or removed? (TBH I can't recall if I let the suspension extend by using the centre stand and having the front wheel off the ground.)

    2) Is that fork seal file available?

    3) Was the bag of charcoal a part of the process? Perhaps afterwards....and with a drink?
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    Great detailed post and bonus points for doing the job right. You highlight the one thing I feel BMW cheaped out on with the F800GT, non adjustable front forks. I changed to a progressive spring and 15w oil to minimize the dive and front end stacking in corners, but you did the whole enchilada.

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    Thanks for sharing what you did. The details are wonderful to look through.

    I wish there was a way to test ride another bike with these emulators alongside my "stock" bike to see what the difference feels like for myself.

    I did a far less professional change to my front forks on my GT this past summer. Using the service manual YouTube video, I drained the fork oil, and then replaced it. I did a few things wrong, like not measuring the amount I drained...which made it impossible to refill to the same level again. The initial feel was the front was rock hard. Too much oil in there. So then I sucked out some oil from each fork...and now it feels great.

    But how great? And that's where I'd love to ride a bike with these emulators to see what a professional change would feel like. It isn't going to happen, but that's my dream.

    Chris
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    Ware, Herts, UK Pat H is offline F800Riders.org Supporter
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    I found the change (on my S ) to progressive springs was the biggest change but that did involve slightly heavier oil as well.
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    1. The caps should press. First try pressing with them on the bike but the front tire off the ground. I like to put the bike on the center stand on top of a strip of plywood. Then with some extra weight on the rear the front tire will come up off the ground. I put 50 lbs in my rear top case. The handlebars will need to come off for that. But I was able to remove both of them with the forks off the bike.
    2. Sure, I can email you the STL file. But maybe I'll post it onto Thingiverse. It should work for any 43 mm fork. https://www.thingiverse.com/thing:4605218
    3. The charcoal wasn't part of the plan. Just an innocent bystander.

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    Quote Originally Posted by Pat H View Post
    I found the change (on my S ) to progressive springs was the biggest change but that did involve slightly heavier oil as well.

    I have learned that fork oil is a consumable and it breaks down with use. As it breaks down the viscosity lowers and the suspension becomes more mushy from less damping. When you drain old oil and replace with fresh you will notice an improvement on both compression and rebound damping. On the stock setup the only adjustment we can make is the fork oil viscosity, with a higher viscosity giving more damping.

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    Even viscosity is not an absolute when you talk about fork oil. I learned a lot last spring when I changed mine. My assumption was that if you asked for a 15 weight fork oil, that's what you got. But there are charts on the Interweb that show the viscosity number is really not standardized across the different brands.

    You can also vary the amount of air in the forks. And the rear shock setting makes a difference in how the front responds.

    Chris
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    Quote Originally Posted by Timskloss View Post
    I have learned that fork oil is a consumable and it breaks down with use. As it breaks down the viscosity lowers and the suspension becomes more mushy from less damping. When you drain old oil and replace with fresh you will notice an improvement on both compression and rebound damping. On the stock setup the only adjustment we can make is the fork oil viscosity, with a higher viscosity giving more damping.
    Mine was definitely shot after 13 years even though just 12K miles. I'm just 150lbs but the ST was bottoming out under rigorous (not radical) braking.

    Hear ya on the track ride. Way to go! I rode the ST on the track a few times, as recent as ~ 2012 when the shock was fresher. Not so bad for sweeping turns and braking if you planned ahead and were smooth - but it was downright scary and chassis upsetting for tight side-to-side quick transitions. (bought a Ducati Monster after that for occasional track use)
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    Ware, Herts, UK Pat H is offline F800Riders.org Supporter
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    I changed my oil when I installed the Progressive springs (around 30K miles I think) And replaced that oil at around 80K miles I'm now on 127K miles and it seems fine.
    With a stiffer front end the oil seals no longer fail (had about 3 go before the spring change) none since.
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    Quote Originally Posted by Timskloss View Post
    .....

    2. Sure, I can email you the STL file. But maybe I'll post it onto Thingiverse. It should work for any 43 mm fork. https://www.thingiverse.com/thing:4605218
    Printing it right now. Thank you!


    Last edited by Runmyownlife; 09-26-20 at 09:27 AM.
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  20. #12
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    Cool. What printer is that? I don't recognize it.

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    Quote Originally Posted by Timskloss View Post
    Cool. What printer is that? I don't recognize it.
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    Q: Tim, How many miles are on your bike?
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    Quote Originally Posted by Kukopia View Post
    Q: Tim, How many miles are on your bike?
    I talked to him this morning because he lives only a few miles down the road from me. When he did the fork job in mid September he had 33,000 miles on it.

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  25. #16
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    That's a pretty cool design you made. Unfortunately for me, it costs over $100 to print on shapeways vs. the metal motion pro version that costs ~$45. It doesn't look like it would use too much material, so I'm guessing the high cost is due to a long print time? I'm not trying to knock your design or anything, just genuinely curious. If I had a 3D printer, I'd definitely print one myself.

    Also, kudos to you for posting it on thingiverse!

  26. #17
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    Quote Originally Posted by rodzghost View Post
    so I'm guessing the high cost is due to a long print time?
    I just checked my printer files and it says I used $3.87 worth of PETG to print with heavy, hammer-able walls.

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