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Discussion in 'Some Assembly Required' started by MotoPolo, Apr 22, 2016.
Man you really did it. And you didn't even have to chop up my old WR450.
Hey Parx how are you??
That old WR is too nice to cut up and it really helped having a working bike to check things out. That was always the plan - just took a while.
I disassembled everything (again) and checked all the suspension travels to see what modifications I might need to make. Here is what I found and my conclusions - please let me know if you see any calculation errors or something doesn't seem right.
The frame was designed to preserve the WR front rake angle with the engine sump parallel to ground so I jacked up the bike, keeping the sump parallel, until both wheels were off the ground. Ground clearance to sump = 298mm
Rear wheel: I measured clearance to ground under rear tire, removed shock linkage, and then raised wheel until it hit something (chain slider on swingarm hit the chain rub block on the tank) and blocked rear wheel. Total wheel vertical travel = 273 mm. I installed Luke's shock emulator and connected linkage. Shock eye-eye = 283mm. Stock shock eye-eye = 395mm. Shock stroke required to hit something = 395-283=112mm. Shock stroke = 95mm.
Conclusion #1 - shock will bottom before suspension components hit
Conclusion #2 - with sump parallel to ground, rear wheel will be below the sump when shock bottoms
Conclusion #3 - I don't need to mess with shock - just tune it and maybe spring rate
Front wheel: I measured clearance to ground under front tire and then using two ratchet straps I compressed the fork as much as I dared. Total compression = 192 mm. I stopped there because one of the ratchets started to bend and I realized that to decompress the spring all the load would have to be one one strap for a bit (spring rate approx 1Kg/mm= 192kg=425 lbs) I measured the change in wheel height at 171mm. Total compression available =300mm equates to 267mm of vertical wheel travel.
Conclusion #4 - steering angle looks right -27 deg (caster or rake)
Conclusion #5 - with sump parallel to ground, front wheel will be below the sump when fork bottoms
Top of Forks are presently about 15mm above triple clamp (lowered to the max). Bike is still too tall. I think I'll try shortening the forks with the Zeta lowering inner kit - this looks like a well designed kit. A couple of the inmates have used it when doing BMW fork conversions. It looks like zeta lowers the fork by reducing the length of the spring perch (30 or 90 mm). That is a pretty slick way to do it as no change in spring length required. A nice bit of engineering as the perch is also a slider??. A spacer (30 or 90mm) is installed inside the cartridge. The damper rod slides inside this spacer. So apparently the mechanism for adjusting stroke length is the damper rod bottoming on the cartridge. So if I just wanted to reduce stroke I could install spacer only.
Conclusion # 6 - try 30mm lowering and investigate revalving for super plush forks.
What ya think?
Take into consideration the possible distort/flex of the tire's sidewall due to different air pressure setting and /or excess force acting suddenly on the tire.That will shorten sidewall height and the ground to sump distance.
If your rear suspension bottoms out, ground clearance will be :
(Ground clearance to sump = 298mm -Total wheel vertical travel = 273 mm )= 25mm
If your rear tire sidewall height reduced by 25 mm (possible scenario for an off-road tire) then your sump will give a sweet kiss to the ground
Is 273 mm your rear wheel travel?
Looking again at your measures : Wheel travel 273 mm with shock stroke 112 mm = linkage ratio of 2,43
With your shock stoke of 95 mm that will give you 95 x 2.43 = 230 mm of rear wheel travel.
What is your rear wheel travel? 273 mm or 230 mm?
Anyway ,even with 230 mm travel a bottom out rear suspension will give you 298-230=68 mm of sump to ground clearance.
A 140/80 tire has a sidewall height of 112mm apx.
Check tire flex if you haven't already , doing that for the front wheel too.
For the rear, maybe look into different shock stop bumpers. If you're not racing/jumping I think it would be worth a try. Make a skip plate to protect the sump, if you don't already have one.
I like that idea - are those available almost anywhere? - Racetech?
Skid plate will be mounted before any serious off road use
Good points Plumer - I supposed good design practice would be to keep the rim below the sump
Disassembled the forks - KYB 48 mm SSS (Speed Sensitive System) sometimes also referred to AOS (Air-Oil-Separate) twin chamber forks. Once they are apart it is pretty clear how they work in general.
Components from top left to right: Inner chamber cylinder, shortened Zeta spring perch (blue), main spring, compression Assy, original spring perch, piston rod with piston assy on left, then Zeta shortening slider (blue), push rod, rebound adjuster lock nut, rebound adjuster, outer tube, inner tube, toes.
Shortening the fork is pretty straightforward. The shorter spring perch (30mm) allows outer/inner tubes to compress 30mm more than stock before achieving stock spring preload. The slider prevents the inner tube from fully extending, maintaining spring free-length preload. The slider appears to be well thought out as o'rings keep the slider centered in the inner chamber cylinder, AND importantly, keep the ID of the slider from contacting the Kashima coating on the piston. So lowering the fork is accomplished by reducing the fork stroke at the full extension end.
The stroke at the full compression end is controlled by the rebound adjuster lock nut.
The rebound adjuster lock nut and the rebound adjuster thread onto the end of the piston rod and lock it to the bottom of the inner tube. If the fork bottoms (fully compresses) the rebound adjuster lock nut hits the bottom of the inner chamber cylinder as shown below.
So shortening the stroke on the compression end just requires a longer rebound adjuster lock nut. There is one small problem which might be overcome. To disassemble the fork you need to compress the spring enough to get the rebound adjuster lock nut clear of the inner tube so you can get a wrench on it. The longer the rebound adjuster lock nut the more the spring needs to be compressed. I am thinking you might be able to machine a step in the longer rebound adjuster lock nut which would allow you to capture it with the little "H" tool.
For the experts on suspension - please correct me on anything I got wrong here but that is what I found from disassembly and looking at a lot of diagrams.
I am going to just install the Zeta kit to start and see where I am. I may install a longer rebound adjuster lock nut if needed. I will probably instal gold valves after I make sure my spring rate is correct.
You need the Zeta fork caps with inbuilt air bleeders to top off the bling factor.
These are a great fork. I am about to fit a set of KYB cartridges to my 4CS forks in my Husaberg.
yes that would add some bling - hard to see those pretty parts on the inside.
Just ordered some more inside bling - The other fork leg had a blown free piston - ordered the Zeta Lt free pistons
Wow, those forks are almost exactly the same as my CRF450R KYB forks internally!
I solved the issue around compressing the forks to fit the rebound adjuster by using a ratchet strap, 1 hook though the axle hole and the other end on the fork cap (rubber coated hooks of course) and works a treat. Just keep plenty of pressure on when you release the strap.
Great idea - I bet the forks are almost or maybe exactly the same
I have an issue with my forks that I could do with some advice on. When I'm gunning it on the dirt they work brilliantly, 10x better than the Racetech'd CRF250L forks, but slow things down and the front becomes difficult to keep in a straight line, its really sensitive to any input. I am assuming it has something to do with the longer forks and the change of triple trees meaning I have changed the bike geometry?
Any thoughts? Maybe lowering them like you have done would fix it? I see Zeta do the same kit for my forks (30mm and 50mm lowering).
Sensitive, or you can't hold the bike in a straight line?
Speed above 50 km/h (where the gyroscopic effect works) without touching the handlebar.
The bike moves to one direction only : bended frame or rear wheel not aligned.
The bike goes left then right then left again and you are unable to hold a straight line by moving your weight : clean,adjust(too tight),change the steering stem bearings!
Touch the handlebar and repeat ,trying to change line with your weight only,.Do you have the feeling that you are going to loose control?Check and measure fork stiction.
Usually symptoms like the one you describe are perceived due to slow response feedback (high latency or lug)
Stiction and tight bearing setup are the main causes.
Ok, I'll check that - thanks!
I thought I had my bearings adjusted correctly but this is quite new to me. I do have a terrribly flattened rear tire at the moment and that's probably not helping. I'm going to change that this weekend first to make sure thats not the issue (or part of the issue).
An old mechanic told me once how to adjust the bearings.
"With the front wheel in the air,put the handlebar in a straight position and leave it.From the time that starts to move to either side it will need 1 sec to reach the stop.Handlebar must have everything -levers -switches- but movement must not interrupted from cables/hoses. "
Since then ,adjusting the bearings become a piece of cake for me.I never got back from a test ride and needed to adjust again.
You may have increased the steering head angle by having longer forks if you did not raise the rear to compensate. I noticed sort of the opposite effect on pavement when I get to speed (>100k/hr) the head starts to shake and the slightest input gets amplified. I'll let you know if shortening the forks helps.
Also are you running a steering damper. I have not installed mine yet but in sand they really help.
I have definitely improved my issue when I swapped out a very, VERY flat MT21 rear tire. I am hoping I can tune the rest out with fork adjustments. I did raise the rear about an inch and the new 120/100 section tire raised it again, maybe the balance has been restored.
I am keen to hear how you get on though with the shortening as it is something I could do as well.
Got my frame back from the plating today. Pretty happy with result. It is so hard to find anyone that will deal with motorcycle or automotive DIY parts. I had several shops tell me they won't even look at my job. TFC plating in Clackamas OR (ask for Luis) did a good job. This is electroless nickel (EN) plating which seems easier to scratch than electrolysis plating. However checking with wikipedia, EN should have good wear properties. I failed to really research what I was getting as I was happy to find someone willing. The frame was bead blasted prior to plating so it has a frosted look. The frame is not as pretty as say the Matisse frames which look to be polished. But I am happy with the result - we'll see how it holds up.
The basic frame kit.
The whole enchilada
Now to re-assemble