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Front End Choices ?


jo1000

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Get a MightyVac, some 1/4 or 3/8" hose (whatever fits the vac), 24mm socket or flat wrench, and appropriate fluids. A front pin stand and a ratchet cinch strap is handy here but an alternate is to use (optional a traditional fork stand - under leg) and an automotive jack to reduce the weight on the front. Or you can accomplish the same thing with an engine hoist and suitable straps tied to the frame or in a pinch handlebars.
 
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I assume 220 -250 cc's is all the oil.  
Try ~450ml. In-place is only doable for partial fluid exchange. To fully replace (flush and/or clean) and then be able to properly bleed the cartridge, off-bike is a must. And you'll need to compress the spring to get the cap off and then back on again. 
You will need something like this: http://www.traxxion.com/Fork-Spring-Compressor-Kit-4017/
Or if you really want to get fancy: http://www.traxxion.com/Fork-Service-Tool-Kit/
 
Otherwise you need to come up with a similar solution.
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I got around to making this change yesterday and went riding today. MUCH BETTER! The compression is much more compliant now! No more harshness! There is still significant dive on braking, so I don't see much change there, but for the 2 hrs of work and $10, this is a significant improvment. Thanks Bruce!Glad it worked for you, pretty cheap effective way to improve the front end compliance & feel. Might try 5-10cc more oil per leg to reduce front end dive, or if you raised your forks a couple more turns of preload. Remember a seminar I attended a few years ago with a Factory BMW Tech talking about the S1000RR. An owner said he thought the front end had too much dive for him & the Tech said add 5cc at a time until it felt right! And for those who have asked, no I don't think you can do this properly without removing the right fork leg.
 
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Thank you... how lazy of me...did not read that through. Taking things apart sounds more fun anyway. Just have to see how to get, and keep the front end in the air.
I wasted more time trying to fit some small hose down the tube with the cap removed than I should have. Remove the right fork, period. It's a 2 hr process, if you go slowly and consume beer. Do NOT be intimidated by this job. It's truly easy. 
Bruce detailed the process nicely in his first post. Follow that, and you're gold. I bought some Rox Shox 2.5 wt fork oil from Amazon along with a Ratio Rite Cup and had a small syringe capable of measuring 15cc.
 
Let me know if you have any questions.
Piedmont of NC
'15 FJ-09
'94 GTS-1000
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What is the reason why I wouldn't be replacing all fluid in the right fork (or both)?... and am I assuming that I should observe volumes up to the maximum specified in the manual
 
re-read http://fj-09.org/post/50831
 
Frankly you should, but it's impossible to do that and keep things on the bike. IMO just buy the proper stand and the hand tools and take the frontend apart. It's not hard.
 
Oil volume is not an accurate way to set oil height. The most correct way is to add oil, bleed the cartridge, and then measure height with a ruler or graduated stick. add/subtract till you get to the number you want. I recommend starting with 160-165mm (stock is ~175) and going as low as 150 (track) but 130 works for more resist to bottoming.
 
If you're not sprung right (check rider and static sag), changing oil height to keep from crashing into the bottom is just a crutch. Do your best stop from ~30mph with a zip tie on the leg. If you can get close to 10mm from the bottom you're ok, maybe add 5ml the next time. If you're much under 10mm I would add 10cc.
 
Fluid level is not critical for normal street riding as long as you're in the ball-park. A *rough* rule of thumb for a starting point is 25mm+max travel. On sportier bikes somewhere around 18+max.
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What is the reason why I wouldn't be replacing all fluid in the right fork (or both)?... and am I assuming that I should observe volumes up to the maximum specified in the manual
re-read http://fj-09.org/post/50831 
Frankly you should, but it's impossible to do that and keep things on the bike. IMO just buy the proper stand and the hand tools and take the frontend apart. It's not hard.
 
Oil volume is not an accurate way to set oil height. The most correct way is to add oil, bleed the cartridge, and then measure height with a ruler or graduated stick. add/subtract till you get to the number you want. I recommend 150mm but 130 works (more resist to bottoming).
I started with 130mm and ended up with 150mm. 130mm was a bit harsh (not as much air cushion).  
A government which robs Peter to pay Paul can always depend on the support of Paul.
George Bernard Shaw (1856-1950)
Bikes:
2015 FJ-09, Seat Concepts seat cover and foam, Cal Sci medium screen, rim stripes, factory heated grips, Cortech Dryver tank bag ring, Modified stock exhaust, FlashTune with Graves fuel map, Cree driving lights, Aux power socket.
2012 Street Triple type R (Wifes)
2007 FJR1300 (Sold!)
 
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So why did I pick approx. 215-230cc's of fork oil to be replaced with 2.5 wt? The oil volume according to the Service Manual is 431cc's in the right leg. If you remove 230cc's of 5 wt and replace with 230cc's of 2.5 wt you end up with a 3.66 wt oil. Was afraid to go any lighter for fear of compression circuit getting too mushy or running out of rebound adjustment. Could probably remove 250-275cc's of 5 wt and still be OK but the 230cc's works fine.As far as adding oil to reduce front end dive during braking, SM says oil level on right leg is 175mm. Adding 15cc's of oil to a 41mm fork gives pretty damn close to a 10mm rise in oil level. So adding 15cc's brings oil level up to about 165mm. If what Pattonme says that 150mm is a good oil level (with a stock fork spring)? then adding 40cc's of oil per leg would get close to the 150mm level. My question for him... is the 150mm level he recommends for the stock springs, which are not linear/straight weight springs but progressively wound and therefore displace more oil than straight weight springs?BTW, it's very easy to add oil per leg. Loosen top triple clamp pinch bolts, loosen fork caps, raise front wheel off the ground, spin fork  caps loose, put a couple of 2x4's under the front wheel to raise it and get access to the interior of the fork, add Xcc's of fork oil per leg, take out 2x4's, tighten fork caps, tighten top triple clamp bolts, remove jack that raised the front wheel. 20 minutes max. Better to add 10cc's or so at a time til you get the feel you want under braking than put in too much and then have to remove the wheel & forks to drain it out! :-)
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If you remove 230cc's of 5 wt and replace with 230cc's of 2.5 wt you end up with a 3.66 wt oil. Was afraid to go any lighter for fear of compression circuit getting too mushy or running out of rebound adjustment. ...
[span style=font-size:12pt]level up to about 165mm. If what Pattonme says that 150mm is a good oil level (with a stock fork spring)? 
[/span]
'W' notation isn't a useful metric - it's not a standard. Not arguing with your math, just saying folks need to find the specs of the oil you want to use and use the cSt@40 values in the formula. Yamaha's default fork oil is ~16cSt@40. (at work, can't look up) 
yes, standard straight-rate springs. 
 
the compression circuit is so choked up you won't need to fear "mush" till you get down into the 'water' category.
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  • 3 weeks later...
they are inter-changable. Shock oil just has a much better VI so it's damping characteristics are more stable across a wide temperature range. It's a side-effect of very little quantity of fluid doing a lot of work, whereas a fork as a ton of fluid under very little stress by comparison.
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  • 2 weeks later...
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Guys, any value in removing the damper rod assembly (by way of the bolt, see #15 on diagram) in order to flush more oil out? Doing the @bruceintucson oil swap thing. Thinking this could just become a giant mess without any measurable benefit and I could lose sight of how much oil I actually have to replace. 
 

You don't need to do that in order to extract the amount Bruce was specifying. And you can see from the drawing that locktite (LT) is used on that bolt, so it doesn't break free without offering blood and skin to the motorcycle gods. Simply unscrew the cap and pour out somewhere between 220-250 cc's of the 5 wt fork oil . 
 
Piedmont of NC
'15 FJ-09
'94 GTS-1000
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It's alright @piotrek outer tube orientation doesn't matter. If you're going to up-end the forks for maximum drain and also not remove the fork cap, then there is a non-trivial chance you're going to have air in the cartridge and effectively no damping. Unless your name is Hulk Hogan trying to bleed the forks while fighting the fork spring isn't going to be fun. You either Mighty-Vac the forks right side up and replace with ~equivalent volume of new oil, or you bite the bullet and take the cap and spring out so you can do a proper bleed and oil height measurement.
 
Or you ride around with somewhat sketchy damping until it gets worked. out. Hard and deep static pumping of the fork using the bike's weight to help compress can work. Set preload to minimum and rebound adjuster fully CCW. You can tell it's good when you set the rebound all the way tight (CW) and it'll come up smooth the whole way and not have a sudden easy spot.
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@bruceintucson ....have you noticed a tangible difference in handling after dropping the front end 5mm?
Define "handling?" The FJ does turn in to a corner a little easier, but it didn't really understeer much before raising the forks. It holds a line better once in a corner and mid-corner corrections take virtually no effort; just look there and it goes there. It seems more balanced front to rear. The two things that are really noticeable are less turbulence-induced twitchiness or hunting from bad side winds or trucks on the highway. The second is much more stability at higher speeds, the front end doesn't get as light and the FJ feels more planted. ECU has been re-programmed so speed limiter is removed and 120+mph speeds are [em]generally[/em] a non issue. This is a stiff (slightly too stiff IMO) bike that has very little chassis flex so it's similar to a sportbike in that it's susceptible to occasional strange handling effects depending on the road & conditions even with upgraded suspension.Depending on your weight (and if you set the rear suspension properly for your weight-most people don't-) 5mm is a minimum. Try 5-6mm to start, then go up 2mm at a time until it feels right to you; you'll know when you've gone too far. It will start to understeer, ie it wants to turn too quickly given an input and will fall into corners and not hold a line. This is probably from my experience on other bikes somewhere around 10-14mm.For each 2mm you raise the forks, try adding 1/2 turn of preload. 
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