Hope some of you find this interesting. It's long, but there are a couple surprises and some interesting findings. The fork is the same on the Sport 1000 also.
Ever since I took possession of the GT I have been riding more and more "spirited" than I ever have before. Most recently I have noticed that the front fork is in need of some improvements to keep up with the pace in the corners and improve comfort on my daily commute. I have wanted to look into checking and adjusting the front fork preload & damping, and from my observations my theory was that the fork was under-sprung and over dampened. Most prominent symptoms were headshake, harsh ride even though the front was sagging, and some chattering. I ordered a triple tree lift adaptor for my front stand, and made a tool to fit the fork caps(
http://www.ducati.ms/forums/showthre...32#post145232).
Here is what I found and did today when I looked into it:
A friend of mine came over so we could check all the suspension measurements on our bikes. He rides an R1, so I thought it would be interesting to see how different the numbers were. We basically followed the same technique found on these websites to figure out our static sag measurements, and also outlined in the book "Total Control" by Lee parks, which we had on hand. They all are pretty much the same:
http://www.sasbk.co.za/suspension_setup_guidelines.htm
http://www.gostar-racing.com/club/mo...ion_set-up.htm
I weigh 160 pounds w/o gear, I did not wear my typical gear when measuring. Original numbers for the two bikes were as follows:
R1
Rear sag w/ rider: 27.8 mm
Front sag w/rider: 55 mm
GT1000
Rear sag w/rider: 28.0 mm
Front sag w/rider: 42 mm
We were surprised that the bikes were so close in measurement and that the rears were very close to the recommended 30mm. We simply cranked down the preload adjusters on the R1 and got the front sag on that bike to 43mm with them all the way in. He will need shims or new fork springs. The R1 has fully adjustable compression and rebound damping on the fork and rear shock, but they felt/rode fine so we left them alone. Of course it’s not so easy to adjust things on the GT.
I set about opening up the forks. I have never worked on an inverted fork, but had a manual for a similar non adjustable fork from a Ducat Monster on hand. The caps do not simply unscrew. They are screwed to the damper rods. Here is how I figured the best way to remove them:
1. Lift front of bike so wheel is un-weighted. This can be accomplished with the bike on a rear stand and using a jack under the motor. The front wheel does not have to be hanging free.
2. Loosen fork caps until they do not come out any further. I had to use a cheater bar on the cap tool to break them free. DO NOT keep spinning them though because they will start dropping metal shavings down the fork tubes!
3. Remove the handlebar because it is directly in the path of the fork caps (GT only). Slowly lower the front of the bike and the caps should lift off the top of the fork. You can lower the bike until to forks bottom out for the next few steps.
4. Hold the fork cap with the fork cap tool and loosen the 13mm lock nut underneath until you can spin off the cap.
At this point I removed the fork springs. I was excited to see how this thing worked because I have felt a scraping in the fork since new and thought it just need to break in. It was really noticeable when the bike was idling at stoplights and felt like a grinding in the motor, but was really a slight scraping in the fork affected by the vibrations at idle.
The first cap I removed had a washer that fits between the cap and spring. The second cap did not have this washer. I thought “just like good old Ducati to forget some parts”. Here is where I found it:
The second washer was mangled up at the bottom of the right hand fork spring. Well, there’s the source of the scraping.
I wanted to speed up the damping in the fork so I purchased some 5 wt fork oil. The stock oil is 7.5 wt. The oil level is measured with the springs removed and the fork legs fully collapsed. I measured the oil level from the top rim of the fork to be 95 mm. The manual I had called for 100 mm, and the forum/web browsing I did determined that typical measurements should be between 80 mm and 120 mm (depends on the brand of fork too). I was not planning to remove the fork legs so I simply siphoned out as much of the stock oil as I could with a little hand pump . I filled each leg back up to 90 mm with the 5 wt oil. I figure the total amount of oil removed & replaced to be about 1/3 of the total. I guess I now have a blend somewhere between 7.5 and 5, which is fine because I wasn’t looking for a drastic change, just wanted to go a bit lighter.
I found out something interesting: The damper in the right leg controls rebound damping, the damper in the left leg controls the compression damping. This means that if down the road I want to individually change the characteristics of either rebound or compression I can change the viscosity of the oil on that leg only! Cool!
I wanted to get my fork preload to be around the 30mm recommended so I need to make some spacers. Luckily I had some thick walled aluminum tubing laying around that fit the cap and spring perfectly. On the R1 we moved the preload adjusters about 12mm and improved the preload by about 12mm. I needed to improve mine by 12 mm to get to the magic 30 mm, so I made 12 mm spacers.
It was a challenge to get it all back together, especially since the lock nut would now be covered by the spacer. I found a large washer and cut a section out to make a slot to the center. I then compressed the fork by hand with the spacer on top down far enough to expose the nut on the damper rod. The idea was to slide the washer in between so I could then screw the top cap back on.
One problem is that on the leg with the rebound damper the damper wants to fall back into the fork. I wrapped a little piece of bailing wire under the nut so I could hold it up while compressing the spring and then slipping in the washer. Does it sound like you need more than two hands? It would have helped….I reinstalled the handlebars temporarily so I could wrap the wire around them. It also helps if you unscrew the nut to almost the end of the rod.
Once the washer is in place the nut will have to be screwed back down to make room for the top cap to thread back on. Screw the cap all the way on by hand and then lock it in place by threading the locknut against it using the fork cap tool and a 13mm wrench. I used a torque setting of “fairly snug”. The slotted washer can then be pulled out. Do both legs.
Next the bike is lifted back up until the front wheel is once again un-weighted. Tighten up the top caps. Once everything you loosened or removed is put back and tight, it is ready to ride!
I measured the new static sag at 28.5 mm.
TEST RIDE IMPRESSIONS:
The fork is totally transformed! I only took it around town and on the freeway a little, but could tell just pulling out of the driveway. Manhole covers and potholes that were once very harsh (I had even taken to standing up motocross style for some bumps) now could hardly be felt. The bike is tracking perfectly straight and stable, no wag or weave. Also, the fork dive under braking does not seem any different than before. I could not believe how much of a difference these little “tweaks” made. This is how it should have been all along. Can’t wait to get it in the twisties to see how it tracks leaned over! It is much more plush, and I think one reason is that mow that the preload is set correctly there is actually a bigger air pocket above the oil. There is also more useable travel. The lighter oil allows the fork to react quicker on both compression and rebound. Oh, and one less mangled washer in the bottom of the fork.
Just goes to show, once again it pays to fiddle and get your bike set up for you and your type of riding!
Thanks for tuning in, and don’t forget, “your mileage may vary"
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