edited by Kristian #562
Updated by Scott, ID, #1244
Please read the Disclaimer before attempting any work in this FAQ.
Last updated 21 July 2006, Winter #1935
For FAQs related to forks, shocks, maintenance and aftermarket options:
This FAQ is in addition to the main Aftermarket Forks FAQ. There are many more options for the fuel injected F650's, and where possible these have been included in the main FAQ.
by Iceman #975
Since most GS's are relatively new bikes with lower mileage, I'm going to skip the fork seal replacement for this upgrade, to make the discussion simple. If you want to replace the fork seals, the procedure for changing them is the same as for a pre-GS F650. The Fork Oil Change FAQ (for Classic F) and the Fork Seal FAQ GS Dakar may also be of some use.
This FAQ is limited to the GS/GSA at present as on the Dakar, the fork tube caps are threaded. I'm also not positive the damping tubes have the same holes in them as the GS's. See below for more information on the fork tube component differences between the Dakar and the GS.
|The Parts you receive from RaceTech|
2# Emulators Part #FEGV S4101
I also ordered 2# Springs Part #FRSP S344380, which are rated at 0.8, however these have not yet been installed as I want to test the effect of each component separately.
|Tools you'll need||Working Supplies you'll need|
Start by lifting the bike off the ground to remove the forks. Remove the two bolts holding the front brake caliper to the fork leg, using the 8mm Allen. The caliper can be kept out of your way by tying it back with some wire. If your bike has ABS, you'll need to remove the speed sensor. Remove it with the 10mm socket, and pay attention to a small spacer/washer that may be between the sensor and the fork leg.
On the bottom of the fork, there's an Allen bolt, which holds the damper tube to the bottom of the fork leg. Loosen it enough just to break it loose, not enough to let fork oil drip out. This bolt can be tight, so loosening it when the fork is out, or with a worn Allen socket can be difficult. Loosen the axle clamp with the #45 Torx Bit. Unscrew the axle with the 8mm Allen, and slide it out to release the wheel. Watch for spacers, there's one on each side, that can drop down when removing the wheel.
Now's a good time to drain the forks of their fluid, OEM fluid is 7.5 weight. With a 10mm socket, loosen the drain plug. Have a drain can available, and while holding it close to the drain, remove the drain plug and allow the can to catch the fluid. If you set the can on the ground first, you're going to miss the can, Murphy's Law applies. After they are completely drained, re-install the drain plug and tighten to 4.4 ft lbs or 6 Nm.
Remove Fork brace with 6mm Allen.
Next, loosen the three fork clamping bolts on the upper (1# for each fork, marked yellow) and lower (2# for each fork) triple clamps with the 6mm Allen. The Allen socket you use should be fresh, a worn one can strip the Allen hole when loosening or tightening. When loosening the third bolt, keep a grip on the fork tube, as it will slide down and drop on it's own, once loosened.
If you decide to hold the fork tube in a vise, you'll need to use wooden
or plastic protectors, to protect the finish of the fork tube. Any nick in the
fork tube is bad, it can ruin the fork seal. Clamp it toward the top of the
tube, and just snug enough to hold it still. Remove the black plastic dust
cover, it pops out with your fingernail. With one thumb, push down on the fork
cap against the fork spring pressure, to expose the inside retaining Circlip.
While pushing down slightly, use the mechanics pick to get behind and pop out
the Circlip. Be careful to have a hand on top, so it doesn't fly into orbit.
Remember, Murphy's Law takes no day off.
This will release the fork cap up above the fork tube with the pre-load spacer under it. Remove the fork cap, the pre-load spacer (looks like a piece of exhaust tubing), the washer and then the spring. Remove the fork from the vise and compress it to bottom it. While it's laying flat on a work surface, remove the Allen bolt from the bottom of the fork leg, and notice a copper washer that should be on the base of this Allen bolt. While keeping the fork compressed, slowly tilt the fork upside down till the damping tube slides out, and set the fork assembly aside.
Carefully remove the damper tube piston ring, and set it aside. Trial fit the emulator to the damper tube top cup. If the fit seems loose, there are snap rings in the kit that fit around the base of the emulator. This expands it's diameter, for a closer fit, and I used them on mine.
You'll notice the two 12mm holes at the bottom of the damper tube.
Measure from the bottom of the tube 2 5/8" or 66mm, and on the back side of the tube
(opposite side where the two factory holes meet), drill a 12mm or 29/64"
hole, starting with smaller sizes first. Chamfer the inside and outside of the
new hole to remove the rough edges from the drilling. Clean the tube from
shavings, and reinstall the piston ring.
Note: For more detailed information on calculating the size of hole to drill. The flow through an orifice is commonly expressed as:
Flow in GPM = 19.636*C*(D)2*(h)1/2
C is the discharge coefficient which is equal to 0.61 for a sharp edged orifice,
D is the diameter of the orifice in inches, and h s the differential head across the orifice in feet.
All that really tells you is that the flow is proportional to the square of the diameter of the orifice and the square root of the apparent head. In this case the larger orifice will have twice the area of the two smaller orifices combined. Flow is proportional to the square root of the apparent head and the coriolis force would act to reduce the apparent head at the orifice." Scott C, posted by Flash#412.
If you are curious enough to want to know the 'spring rate' of your springs you can learn how to calculate it by reading the Spring Rate FAQ.
Clean the hole at the bottom of the fork leg, and the Allen bolt that holds the damper tube in place. I use a dab of RTV black silicone at the base of the Allen bolt. When dry, it helps seal the bottom of the leg. You can re-use the copper washer on the Allen bolt, or replace it if the forks have previously been apart. While holding the compressed fork assembly upright, start to re-thread the Allen bolt up into the damper tube, and make snug.
The emulators need to be adjusted before their installation. Loosen the 3/8" locknut on the bottom side, and unscrew the Allen adjuster until the adjuster spring is neutral. Turn the adjuster to two turns in, for an initial setting.
Re-mount the fork into the vise, and leave the fork compressed. Pour 550cc of fork oil into the fork tube, and pump the fork assembly to get the air pockets out of the fork. When you can't see bubbles looking down into the tube, you're done pumping. Drop the emulators into the fork tube, and let them settle down through the oil. With the fork compressed, measure from the top of the fork tube to the top of the oil level. RT calls for a fluid height of 120mm from the top of the fork tube, so adjust this fluid height accordingly. You may wish to consider changing the weight of your fork Oil to 10 wt.
Extend the fork leg, and add your choice of spring, RT recommends their springs for a higher tension. The washer goes back in, then the preload tube, then set the fork cap on top.
If you want a factory pre-load, you need to cut off 12mm (the height of the emulator) from the pre-load tubes. Hacksaws rarely cut straight lines, so if you have access to a tubing cutter, use it to make your cut. Many owners may not have a large enough tubing cutter available. If you must use a hacksaw, fit a stainless hose-clamp around the pre-load tube and tighten it down at the line to be cut. The hose-clamp will act as a guide, then use a flat file to clean off the sharp edges.
RT calls for a pre-load of 20mm, which means you're going to compress the spring 20mm as a head start. Measure the distance from the top of the fork cap, to the top of the fork tube. Since the top of the fork cap sits recessed into the fork tube by 10mm, cut the pre-load tube so the top of the fork cap top will sit 10mm higher than the top of the fork tube. Now, when assembled, the pre-load is 20mm. Push the fork cap down against the spring, and re-install the retaining Circlip.
Slide the fork leg back into the triple clamps, and tighten them to 18 ft lbs, or 25 Nm. Refit the front wheel, making sure your spacers are in place, and tighten the axle to 58 ft lbs. or 80 Nm. Do not tighten the axle clamp yet. Install the caliper, and tighten the mounting bolts to 37 ft lbs or 50 Nm (I use Blue Loctite here, and on all critical fasteners). The ABS Sensor has a tightening Torque of 4.4 ft lbs or 6 Nm.
Install fork brace and tighten bolts to ____ ft lbs or ____ Nm.
Take the bike off the stand, and compress the forks a few times to set the axle to center.
Now tighten the axle clamp to 17 ft lbs. or 23Nm. Tighten the damper tube bolt on the bottom of the fork leg to 14 ft lbs or 20 Nm. Pump the front brake lever until the pads meet the rotor, sometimes the first pump feels like there's no brake.
Now you're ready for a test ride, then a re-check of your fasteners.
1) To adjust your forks, note the following:
A heavier Fork Oil will increase Rebound.
Tightening the Emulator Adjuster will increase Compression.
More pre-load will raise the front ride height. I've re-adjusted mine to 2.5 turns from neutral, and will keep experimenting as I feel necessary. David #476 says it only takes 15 minutes to re-adjust, but I've had less practice.
If you have a Dakar, there are a couple of differences. First, the fork tube caps are threaded in, like the Classic F, not held in with circlips. Loosen the upper fork clamps first, so you can remove the caps. If you don't loosen the upper clamp, you'll end up stripping the hex off the cap, since the clamp squeezes on the threads. When tightening the cap during re-assembly, tighten the lower triple clamps first, then tighten the fork caps, and finally tighten the upper fork clamp last.
Another difference may, or may not, be a difference in the Dakar damper tube holes. Since I've never seen a Dakar fork apart, I'm assuming the damper tubes are probably longer, but have the same holes. If they do, drill the same 12mm hole in the same place in the tube. If they're smaller, you'll need to a drill different sized hole(s). Basically, if there's a difference, post the difference, and I'll reply with an answer.
Since the Dakar has a longer travel in the fork, It may require more fluid for an initial fill, and perhaps a larger distance from the top of the fork tube, for the fluid height. Since the stroke is longer, it may require a larger air volume in the top of the fork. I'd guess 140mm from the top, or the factory setting. The higher the fork oil level, the more resistance to bottoming (inner fork, air compression).
After searching through the Race-Tech site I was surprised to find no listing for the for the 04-06 GS. All the FAQ's also seem to only address the older models. Does anyone know if the FEGV S4101 emulator's will fit into the 06 GS (non Dakar) forks or are springs and oil my only choice? ... It appears after looking at the parts fiche on the A&S BMW website that the 99-05 GS and the 05-up Dakar models use the same damper rods. The 04-down Dakar model has a different part number for the damper rods. cadhopper #2041
I just received the TT springs for my GS. Next step is to get fork oil and decide how much to use. I've read the spent-shun knowledge and experiences in the FAQ which were very helpful. The reason for the upgrade is excessive dive and sag. First I should say that I am a big boy - scaring the h*ll out of 300 lbs., just over 6 feet tall with a 32 inch inseam - seat height is not a problem for me. My fork sag is about 2.1" (~53mm). The bike has about 10k mi. and is mostly road ridden. The FAQ says it should be set to about 1" (~25mm). Touratech recommends 575ml of SAE 15. The FAQ says 600ml of SAE 7.5 or 10. I think the 25ml difference is because the TT springs are larger. I guess I'll start with 575ml of SAE15 and see how the bike handles and see how much sag I have. If the sag is more than an inch, should I add a little more fluid or put a longer preload spacer in? The rear seems to work fine with the re-bound and the pre-load both set at max. Any wisdom is appreciated. Kevin #1092 Black 02 GSA
I just finished my conversion. Ohlins Dakar shock and Dakar forks with Touratech springs. I did not have any problem with the shock, other than working around the abs box. I have got around 200 miles on the setup so far (mostly dirt) and it seems to be working fine. I still have the 19" front wheel. I bought the complete legs. I wanted to keep the standard GS parts intact in case I wanted to switch back. Got the shock through Mr. Eds at a good price, 750 versus 1100 list. Forks were around 800 versus 2K for the Touratech w/p forks. So far I love the change. Much more confidence inspiring on rough roads. I have only bottomed out once in a few hundred miles instead of the previous 2 to 3 times every ride. A small price to pay for my lack of foresight in not getting the Dakar in the first place. Mike819 in Reno 01 GS
Another thread I started earlier today discusses this. Not stated there is that I used 10 wt oil and my riding weight is about 200. First I would get the oil level correct as Richard and Mark suggest doing in the other thread. Then I would make some PVC pipe pre load spacers starting at the same length as the OEM ones and start testing. The PVC is easy to cut and if you screw up you still have the steel ones for back up. My spacers ended up as short as I could make them and still have any tension on the spring. Yours will need to be longer of course. Adjusting the oil level is going to have a different affect on handling than changing the spacer length. Too much oil results in a smaller column of air and that compresses less so it has the affect of stiffening the forks during the compression stroke. The spacer length will let you dial in the sag you want. I'm no expert of course so YMMV. In my opinion, if you use the bike on a variety of roads, especially off road, precise tuning is not practical. The requirements vary too much between them. In keeping with the design of the bike itself I just aim for a decent compromise. BTW I'm not sure setting the rear compression damping to maximum is the best way to go. If you have not tried it yet I would back it off some if you find the bike hops around any on the bumps (1/4 - 1/2 turn). Another thing I would suggest. Compare the length of the OEM spring and the TT ones. I betting the TT springs are longer by noticeable amount. I can't recall exactly by how much but mine were longer which added to pre load so much I couldn't get the caps back on. Brad, N. CA., 2001 F650GS - Inmate #1002
I added the Ohlins to the rear and LOVE IT! I also did a RACE TECH cartridge emulator install to the GS fork tubes and added a bit of preload to the front suspension. I still have the 19" front wheel but am considering moving up to a 21" front wheel. The front has only bottomed out once or twice. I did not add a chain roller but you will have to modify the center stand. I have 6000 miles on this set up and it works great. Race tech added 20 mm of preload to the fork and so the forks are now 15mm shorter than the Dakar forks. That's about a 5/8 inch difference. The forks may not have as much travel, but they work a lot better and are less bouncy. I would like to eventually get the whole Dakar set up for the front end - but so far I can't decide whether to go with the Touratech setup or not. chrislindau
My big question is for Chris. How does the RACETECH modification add to front suspension length? Did this include new upper fork tubes or does the cartridge change include a longer rod which lets the slider move down on the upper fork tube? As for pre-load, all that is going to do is reduce sag. The bike may sit a bit taller as a result but no way reduced sag alone makes up for the ~1.5" difference between the GS and the Dakar (the BMW web site does not seem to display the Dakar specs any longer but I remember 1.5"). Brad, N. CA., 2001 F650GS - Inmate #1002
Maarten, I'm looking to do the same thing to my bike. I emailed Touratech in Germany about this, asking the same questions as you; they return emailed me saying I needed a new "lateral upright" which shed no light on the matter and Touratech USA was of little help. I'm guessing that one of the rear suspension components (either of the smaller levers connecting the swingarm to the shock) must change but don't know which one although from reading this string, it seems as though people are doing just by changing the rear shock. There's a little on this topic in the FAQ's but it's limited. Iceman says you need to weld a chain wheel bracket to the frame; he doesn't say where but I'm guessing it goes below the bottom edge of the chain to keep it from hitting the frame when the swingarm is down though reading this string, it would appear this is not necessary. Do you have any more info on this? I would also think a different calibration may be required for the ABS controller and maybe the ECM if you change to a 21" front wheel. It was mentioned that the front forks could be modified, but not how. I was hoping to hear from someone who'd actually done the conversion. You seem to have answered my question in part. I guess I really need to take one fork apart and do some measurements to figure out what to do. I'd go down to the dealership and compare part numbers on the microfiche but the dealer here is pretty hopeless and getting the parts people to help out like that is unheard of. I want to do the conversion but want to spend as little money as possible doing it so hopefully converting my current forks rather than buying new ones will save me some money. Thanks, Nathan 02GS
I guess Touratech
wants to sell their WP suspension setup. When installing their 250mm rear WP
shock on a Dakar, no new parts are necessary. I tried to find any differences
between the GS and Dakar parts but couldn't find any. As some people explained
here the longer shock should fit the GS, no new parts needed. Does anyone know
how much longer the Dakar shock is? My guess it's about 10mm longer. As for
the chainwheel bracket, you don't have the weld it to the frame.
Fabricate a piece of metal strip and connect one side to the two lower bolts of the right footrest support. Bent the strip upwards following the contour of the frame and connect the other side to the rear brake cylinder support. Now weld the chainroller to the strip. (not so great explanation but i hope you get the idea) There's a picture on DHP site under modifications showing the Touratech footrest and the chainroller. I don't have ABS on my bike but i guess there is no differences in ABS hardware between a GS and Dakar. Hope this helps a little. Maarten.
The real differences between the GS and Dakar suspension are the fork tubes and damper rods. Might be some spring rate or coil dimensions difference, too. Damper rods for a classic are about $90 if memory serves, so that's ballpark. No idea on the fork tubes, but I'll bet they're pricey from Bring More Wallet. You'd probably be better off buying DHP's Dakar forks. Harl #380
Used forks are certainly a way to go. They may not always be available. I'm pretty sure there are a few people out there that would do it if the cost was reasonable. The whole new fork is $475 each (per BMW). Here are some prices for the big items: Down tubes ($172 ea. per BMW); Caps for them (the Dakar's are threaded, or buy Hondas with pre-load adjustment for $40 ea.) springs (go aftermarket on these anyway, about $50 ea.) Damper rods ($109 ea. per BMW) That may be all there is to it. The bottom sliders are exactly the same. The diameter is exactly the same. So for $371 ea. you can convert. That is only a saving of $104 ea. or $208 on the set. You might get a discount on the $475 so it might be less. Unless you like working on stuff yourself it is obvious the way to go is a whole new fork or a good set of used ones. I would do all the work and a Race Tech mod at the same time so personally I would just buy the parts. It could always be converted back if need be. Brad, N. CA., 2001 F650GS - Inmate #1002
You may want to check with Forks by Frank to see what he might be able to provide in the way of NON-BMW fork tubes. Marty #436.
Parts list error. The Honda adjustable fork caps will not fit the Dakar tubes. The Dakar has threaded caps but use a coarse thread. The pre GS fork tubes use the same fine thread as the Honda's, and are also identical to the GS tubes in dimension, except for the threaded cap (the GS uses a non threaded cap held in by circlip). If you want preload adjusters on a Dakar, the caps can be center drilled for air fittings. If you bend your non threaded GS fork tubes, you may get threaded fork tubes (pre GS style) as replacements from BMW by accident. When I ordered mine a year ago, BMW had the wrong numbers and were sending the wrong tube. I spent two weeks trying to figure out what was up, and no one connected to any part of BMW knew why the new ones were threaded. They may have updated the part numbers by now, or perhaps not. If you want adjustable Honda caps, you need to use pre GS tubes. If you want to run a 19" front wheel, and want improved suspension, keep it simple. Buy good springs, Race Tech emulators, and use 10w fluid. This is what I run, and I rarely bottom the forks, if ever at all, and it's the best front end action I've ever had. If you want taller Dakar suspension for more travel and to use the 21" front wheel, the true cost is only fork tubes and damper rods (BMW calls them tubes). The cost of real springs and the emulators are an improvement to any of the F650 front ends, and should be considered for anyone wanting an improved front end. If you want to cut corners, have a sleeve welded in the GS damper rods to extend them to Dakar spec. A properly welded sleeve will be no weaker than the 8mm bolt that holds it to the fork leg. If I remember correctly, they have a factory weld on them to begin with. Iceman.
Thanks for the clarification on the fork caps. Too bad. Installing air valves in the OEM ones sounds possible. Wonder if anyone has done it on a Dakar. No matter what, the conversion to Dakar tubes will require a new cap. The standard GS tube cap is clipped not threaded. I'll have to get a price for it. I think you're going to need new springs for the Dakar conversion. You could install a longer pre load spacer but will the shorter spring have the compression range needed, I don't know. That's 6.69" v. 8.27" (or 40 mm increase in travel). My Touratech springs were longer by 20mm than the standard OEM springs. That might be close enough. Brad, N. CA., 2001 F650GS - Inmate #1002
I have the TT springs (Orange Props to K7lro - Thanks, chief!) and I use 15wt oil.
Yes, it's a stiffer set up. Yes, the bike will require more rider attention. The TT springs/15wt set-up is best suited for high speed riding over two track terrain. You'll track through stuff a lot better without feeling like you've surrendered rider input to the terrain's desires.
Flipside.....In technical terrain, you'll need to be up on the pegs a lot to prevent getting bucked off. Mashing into steep transitions will have a tendency to wake you up from the total bike rebound. At your weight, I suspect you'll be fine. My little bantam a** (160lbs) has to really be 'nuts-on-tank' to mitigate getting tossed off.
The trade off......Anything less in the forks will have you bottoming out on those sharp transitions in technical terrain and schwacking your wheels when you gotta hit the throttle to power through stuff. With a soft (near stock) set-up you'll stall your momentum trying to clean an obstacle. For the times I've been bucked off, I gladly accept those for the times I've been able to clean some tough stuff and the hundreds of times I've ridden two-tracks at insane speeds.
From Touratech website:
Fork springs BMW F650GS Dakar $111.30
Progressive and harder than the original springs
Better damping with off-road use
Easy to fit
Use 575ml, SAE15, Install with tighter-wound coils down
And that's it. Don't forget to anneal your copper washers if you're not able to run to the store and get some new ones. That tip came from the ever-helpful Haakon. -NothingClever
Installed a set of TT fork springs today. The stock Dakar spring is 475mm long, and the TT spring is 470mm. I'm starting with #10 oil, and will try the TT recommended #15 if I still bottom out with the #10. Also, I'm using 575 ml of oil (per TT), not the 550 ml shown in the BMW owner's manual. After installation I have 30mm of sag, whereas I had 25mm with the stock spring. I suppose this is because the stock spring is 5 mm longer than the TT? -Scott, ID, #1244
The stock springs I removed were certainly not wound progressively.I replaced them with 'progressive springs'(Wurth actually)from Touratech ordered through Motorworks(www.motorworks.co.uk)About £65 IIRC.Handling on tarmac much improved and dive on braking much reduced.Well worth fitting IMHO.Not tried offroad yet. -tall tony, '02 F650GS Dakar