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F-Twins Tech - F800GS Renewing Fork Seals

We want to gently remove each of the pieces. Again I used the plastic tool, twisting in the slot of the brown bushing, and removed it from fork leg.

We can now slide off each piece, making sure to keep them in proper sequence and orientation.


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This is a picture of everything laid out in the proper order and orientation.

Note: #1 is closest to where the tire is held on and everything is faced down (if you were looking up at the handlebars from the tire's perspective).

1: Dust seal (new seal above)
2: Oil seal retainer ring
3: Oil seal (new seal above)
4: Metal washer
5: Silver bushing
6: Brown/black bushing

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We can now reassemble the fork. Again, please pay attention to the orientation and order of each of the parts. I use a thin plastic bag, coated in some fork oil as to not tear or mar any seals as they slip over the hard parts of the fork. You can buy special fork tube protectors, but I found that this method works fine and is a bit cheaper.

First, you'll slip on the dust seal (spring facing the axle part of the fork). Then, you slip on the oil seal retainer ring.


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The oil seal is next, making sure you have the correct orientation. The top "spring and lip" would face towards the axle, whereas the bottom "swimming pool" would face towards the bushings.

The arrow is pointing with the orientation towards the axle.

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We can now reintroduce the chrome fork tube into the gold top tube. Be gentle and don't force anything. The small amount of fork oil that was on the plastic bag when we installed the seals and bushings should help everything slide.

This picture shows the oil seal pressed into the recess of the gold tube. It is not yet driven down to it's final place.

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We can now assemble our fork seal driver tool and seat the oil seal into its proper place. It generally doesn't take too much force to drive the seal into its home. A helper may be nice to have here, as you need to hold the axle portion and the dust seal away from the area you are working on.

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We then slide the snap ring down and pop it into the machined groove in the gold portion of the fork. I found it works best if you get the opposite side of the opening into the groove first, then use your plastic tool to gently push the rest of it down. One way to know if the oil seal is in the proper place, with the snap ring also in the proper place, is to note if the ring will rotate in the groove with a little force. If it does, then everything is where it needs to be.

You want to be sure everything is in the proper place, because if it isn't, your first ride will have you and your bike covered in fork oil.

This is a hard photo to make out, but you can see the snap ring (which pretty much disappears) in the proper place, holding the oil seal.

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We can now slide down the dust seal. I found that a tiny amount of fork oil or rubber-safe grease helps the dust seal slide into place. Make sure you wipe off any extra on the outside and top of the seal, as we don't want to attract dirt.

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Now it's time to refill the forks and get them back on the bike.

The 2013 and newer F800GS's WP forks call for an air gap of 61 mm when the fork is fully compressed and the plastic inner damper rod is full. To measure this air gap, you can purchase the proper BMW tool from your dealer (BMW Tool number: 31 6 551), use an aftermarket tool such as Motion Pro Fork Oil tool, or the newly-released Thom Rieck's multipurpose, eco-friendly, and dolphin-safe amazingly wonderful Fork Oil Poker Tool (Patent-pending 2019) available at only the most exclusive of motorcycle dealers for $24.95 , which is also known as a chop stick with a red pen mark at 61mm.

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Slowly draw the plastic inner dampener all the way up and push it all the way down several times to move the fork oil into the damper. You will notice that as the damper rod is filled it becomes more difficult to move the damper rod.


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Once the bubbles in the fork oil have settled and you have made sure the damper rod is all the way at the bottom of the fork and the fork is fully compressed, slowly fill the fork with the remaining oil until you achieve a 61mm air gap. You may not use all 610 milliliters of fork oil, so continually check the air gap as you get closer towards the end of the bottle.

If you using the chopstick (DrNeo's wonder tool ), align the mark we made on the edge of the chopstick with the edge of the fork tube, and fill the fork with fluid until the fluid just touches the bottom of the chopstick. Take your time, as it's not easy to remove excess fluid.

Note: this picture shows the chopstick partially removed

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Congrats - you've replaced you fork oil! We can now install the top cover to the fork and begin replacing the fork onto the bike.

First, screw the locking nut on the plastic piston dampener all the way down. Next, pull the piston rod all the way up, so it's fully extended. Then, carefully slide the fork spring over the dampener rod. Finally, screw the top cover back onto the plastic dampener rod. This may take take a little bit of coordination as the dampener rod has a tendency to want to slowly retract down.
 

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Once the top cover is screwed all the way down, we can screw the locknut up tight against the top cover using the 13 mm open ended wrench and 24mm socket on the torque wrench. The torque for this locknut/top cover is 15 Newton Meters (11.1 Foot-Pounds, 133 Inch-Pounds)


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We can now put the top cover back onto the fork. Slowly meet up the bronze-colored upper tube to the fork tube and screw the cap down until it's about 80% complete. Using a bit of fork oil and your finger, lubricate the o-ring on the top cover with a bit of fork oil, then tighten the top cover to hand tight.

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We can now install the fork leg back into the bike. You'll notice that the top of the fork has a single grove machined into it almost at the top of the fork; this is where the fork should sit on the triple tree.

The process to torque the pinch bolts on both the upper and lower portions of the triple tree is a bit unique.

Tighten up the bottom set of two pinch bolts by using your T45 star bit. Each bolt is torqued to 19 Newton meters (14 Foot-Pounds, 168 Inch-Pounds) each time it is tightened. Starting on the top bolt, torque this pinch bolt, then torque the bottom pinch bolt, and continue going between each bolt for a total of six times (each bolt is torqued three times).

In the picture below, you torque bolt A, then bolt B, then bolt A, then bolt B, then bolt A, and finally bolt B. Continue going between each bolt for a total of six times (each bolt is torqued three times).


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Tighten up the top two pinch bolts by using using your T45 star bit and torque wrench.

This process is the same as the bottom pinch bolts:

Each bolt is torqued to 19 Newton meters (14 Foot-Pounds, 168 Inch-Pounds) each time it is tightened. Starting on the top bolt, torque this pinch bolt, then torque the bottom pinch bolt, and continue going between each bolt for a total of six times (each bolt is torqued three times).
(In the picture below, you torque bolt A, then bolt B, then bolt A, then bolt B, then bolt A, and finally bolt B.)

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Now we can tighten the top cover of the fork leg. So using your 24mm socket, tighten the top cover to 40 Newton Meters (29.5 Foot-Pounds, 354 Inch-Pounds).
 
Move on to the other fork leg and repeat the same process. (We will call this the "second fork" for the next process)

Second fork out, drained, refilled, and top cover screwed on hand tight.

To prevent the forks from binding as we ride, we will use the front axle to make sure that both forks are aligned properly.

Install the second fork leg so it's again properly lined up with the machined groove on the top of the fork leg/steering head yoke, and hand tighten the top two pinch bolts. Then install the front axle.

Next, loosen, and then tighten the top pinch bolts using your T45 star bit and torque wrench. Again the unique process: Each bolt is torqued to 19 Newton meters (14 Foot-Pounds, 168 Inch-Pounds) each time it is tightened. Starting on the top bolt, torque this pinch bolt, then torque the bottom pinch bolt, and continue going between each bolt for a total of six times (each bolt is torqued three times).


Then tighten the bottom set of pinch bolts using the unique process: Each bolt is torqued to 19 Newton meters (14 Foot-Pounds, 168 Inch-Pounds) each time it is tightened. Starting on the top bolt, torque this pinch bolt, then torque the bottom pinch bolt, and continue going between each bolt for a total of six times (each bolt is torqued three times).


You should be able to easily draw out the front axle without any binding. If you notice any binding, then loosen up both top and bottom pinch bolts on the second fork leg and torque them back down.


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