09 Forks Strip !

cimwill · Mar 10, 2009

Just pulled the forks on the 09. I have a new set of WP .46 springs to go in and thought I would take a look at what was there, with an eye to stop the fork running through the stroke as easy.

Oil height 135 Dumped first surprise. Should be 110 undumped by the book. Maybe this is part of the problem.

Base Stack
24.1 x 7
23.1
22.1
21.1
20.1
19.1
18.1
17.1
16.1
14.1
12.1
9.5 .3
16.25

Mid Comp.
18.1 Thought there would be 2 here a la KTM
20.1
18.1
16.1
11.4 float 0.6-0.7

Reb.
D20.1 x 3
12.1
16.15
14.15
12.15
14.25

The rebound looks very stiff in the high speed, I guess to control things after it get moving with the bleed shim.

I have two lines of thought know that I know the oil height. Put the stiffer springs in and add a couple of 24 to the base LS and set the oil to about 110.or pull the bleed shim in the mid redo the HS rebound set oil 110 and stiffer springs.

The shocks off too I think it will give it a 2.5mm limiting spacer to give the bike a bit of anti-dive, in the geometry.

Any input welcome.

Chris

Smorgasbord · Mar 10, 2009

If the stock springs are stiff enough to maintain a reasonable static ride height you might benefit from trying to sort the other things first, before changing the springs.
Adding shims to the base stack is generally a good idea, as many as you can stand.
Allows loosening on the adjusters a little bit (especially rebound adjusters) and making the suspension less taut but still resisting wild excursions like dives and such.
Pulling the bleed shim in the MV would weaken the stack so maybe its better to just replace it with a full 20 mm, or just let the 18 mm face shim and the 20 change place. Personally I think that MV bleeds should ideally be drilled holes through port walls as maybe rebound becomes somewhat less obnoxious that way than with bleed shims. If you need the MV bleeds at all.
Do have a look at how Bushmechanics did the BV high speed by using flexy stack deflection limiters on the base valves instead of rigid ones, very interesting reading.
Also, new oil will be firmer than broken in oil. If the forks are feeling a bit on the stiff side when the oil is new then just wait and see if they are not approaching the soft side when its time to change oil.

Just some thoughts. Have fun.

Regards

bushmechanic · Mar 10, 2009

FWIW those face bleeds don't make me happy in any application

I would be tempted either to use a 1 or 1.2mm bleed hole in the mid (SXS MV is identical to yours but gold and has a bleed hole)

or perhaps try moving the bleed one step out

20
16
18
18
11.4

rebound looks good though how it actually works is another thing, guess I like it because I prefer to soften the initial rebound and stiffen the HS if changing anything..

that BV is great for the 12mm rod, finally WP got soemthing right :lol:

another interesting read is smorgasbords post in the big fork thread hes got a different approach for rebound, I like it so much I stole it and use in a lot bikes

thanks for posting the stacks, have fun

cimwill · Mar 10, 2009

From what I have measured the free bleed is give and take about 2.4 mm2. I am thinking this is mostly for the rebound to balance the pressure and the float is for the LS in the mid valve.

The rebound with the current set up is fine if the clicker is well open if you close it down to say 15-17 the front tracks very well but it will also make the front tuck straight after you turn in and pack on braking bumps. The tuck will happen even at very low speeds as if the fork does not extend just as it is unloaded, so with the blead shim and an open clicker its not to bad any idea were I should go with this ? If I remove the bleed shim and drill a 1.2mm hole I will have less bleed and I my make this worse.

Chris

popup · Mar 10, 2009

i gather the 09 has a smaller piston &ports on the mv/rebound.
whats the rebound tap look like?does it allow more flex on the mv shims ,like the zp3 mod?
any chance of posting a couple of pictures chris?
..weed..

cimwill · Mar 11, 2009

Not sure how to post pics here, the taps are same as before with a longer 11mm shoulder so you don't need so many 11mm shims to set the float and the piston has a smaller dia. 22.67mm O.D. Mid spring is 0.6 wire with a free length of 8mm.

The more I think on this the more I believe the LS rebound is not fast enough hence all the the bleed, control on long stroke movement seems ok.

Chris

bushmechanic · Mar 11, 2009

doesn't the 20 fold over the 18 on rebound and almost close it off sometimes ?

whenever i tried a face bleed like above it packed inconsitently for long stroke movements. rebound becomes inconsistent.

just FWIW since ideas are cheap: my approach to rebound is to have it very soft initially but ramp up really really quickly so it neither packs on small bumps (not too stiff LS) nor wallows on long stroke LS rebound (not too soft for same speed but longer stroke).

thjis may be the idea with the 18 bleed shim but as you said it packs sometimes. so its a great concept poorly excecuted by WP who perhaps saaved money by not drilling a hole?

FWIW I just did a KX250

1.2mm bleed at mid,

rebound faced in lathe 0.5 degree prelaod
0.05 thick xover and V light first stage

without machining say the rebound x over is 0.11 thick, using 2 crossovers at 0.05 thick distributed through the face rebound shims makes the forks pack less without wallowing

could have done
2x18D
12x0.05*********
2x18D
12x0.05*******
16x0.11
14x0.11
12 pivot

I think if WP really wanted the bleed to be just for rebound they could have put it on the rebound side with the rebound shims like this

12x0.05
23
23
13
22
18
14
2x11x0.25

found in a cr500 fork tuned by well reputed aussie tuner

again just FWIW since there are a few zillion ways to skin a cat I find that initial harshness is reduced by a bleed hole in the mid without blowing through any worse. same goes for the bleed stage in the stack even though its a tiny MV spring taking up the float it can be felt

so

20
16
18
18
11

feels nicer than

20
18
18
16
11

just some ideas, perhaps not all particulary bright

its all fun this stuff

Smorgasbord · Mar 11, 2009

bushmechanic said:
doesn't the 20 fold over the 18 on rebound and almost close it off sometimes ?

Maybe a little bit of fold over, maybe a little bit that the stack support from the port edges doesn't go all the way around the port openings because of the 18 and that the entire stack flexes to shut the bleed at longer strokes.

The bleed shim in the MV can work a little like the waste valve in a ram pump at rebound.
Not so good in suspension perhaps, it slams shut.
http://www.lifewater.ca/ram_pump.htm
Regards

cimwill · Mar 11, 2009

Ok, here is what I am planning.

Reb. Original----------------------- Reb. New
D20.1 x 3--------------------------- D20.1 x 2
12.1--------------------------------- 12.1
16.15-------------------------------- D20.1
14.15-------------------------------- 16.1
12.15-------------------------------- 15.1
10.3--------------------------------- 14.1
14.25-------------------------------- 12.1
--------------------------------------- 10.3
--------------------------------------- 14.5

Piston, drill a bleed 1.2mm in the web instead of 2.4mm bleed from shim which is possibly varying.

Mid Origina-----------------------l Mid New
18.1------------------------------- 20.1 x 3
20.1 x3 --------------------------- 18.1
18.1------------------------------- 16.1
16.1------------------------------- 11.4
11.4 float 0.6--------------------- float 0.7

Oil height increase by 25mm and 0.46 springs.

On the right track or not ?

Chris

bushmechanic · Mar 11, 2009

On the right track or not ?

you'l find out

stacks look good but thats easy for me to say from here.

I think smorgys pointed out what happens with the bleed shim on rebound, the 18 falls into the valve body and the 20 seals off where it can.

I think without being fancy and using 0.05 thick shims in the rebound something like

1 20 face shim
16 0r 17 Xover
rest of rebound stack

could possibly have a similar result IF thats what you wanted.

cimwill · Mar 12, 2009

Thanks Bushie and Smorgas it's good to sound things out it makes you question things from different dangles and see the wood in the trees. I found a couple of 11s so I will drop them in to shore up the HS and build it up.

Thanks for the support.

Chris

cimwill · Mar 13, 2009

As Built:
Comp.
24.1 x 10
23.1
22.1
21.1
20.1
19.1
18.1
17.1
16.1
14.1
12.1
9.5.3
16.25

Reb.
D20.1 x 2
12
D20.1
16.1
15.1
14.1
12.1 x 2
11.1
10.3
14.25

Mid
20.1 x 3
18.1
16.1
11.4 Float 0.7 1.2mm bleed hole.

0.46 springs, oil 5wt 110 dumped.

Chris

bushmechanic · Mar 13, 2009

nice to see some real proper stacks

its a real bike after all

if its too harsh that bleed stage thing might be worth a try on the mid or maybe some small port BVs fill em with epoxy and drill a smaller hole through the epoxy

Smorgasbord · Mar 13, 2009

I hope that the rebound stack did not get too soft now. I was thinking that the -09 rebound stack was looking quite good. A 0.15 shim is very stiff in comparison to a 0.1 mm shim. About 3.4 times stiffer than its .1 mm counterpart. Replacing a 0.15 shim with a 0.1 mm shim is an enormous step in the softening direction.

I think maybe that if it had been my forks I would have kept the stock rebound stacks for now, if anything at all I would possibly have replaced the 12.1 splitter with a 16.1 with 2 or 3 mm cut off on one side to mimic a 12.1 splitter for ONE of the three delta shim stack flaps, or just replace it with a 12.05 if I had any, but basically start with the stock rebound stack.
With the 1.2 mm hole that you now already have, the mid bleed works a little in both directions and in which case the rebound stack shouldn't be too soft.

Apart from that I believe in your stacks, possibly with another 9.5.3 on each BV OR reduce the diameter of the 16.25s a little bit,? to soften extreme HS impact...?

Again these are just some thoughts from my side, easy to have them thoughts at this distance.

No, theories won't do, the bike is real so it's real trial and testing only that will provide the answers in the end, you are totally right about that Bushie,

Regards

cimwill · Mar 13, 2009

I have not done the maths, but release that the mid/rebound will now have a good bit less oil to work with owing to 23mm cartridges.It was still in my mind as I was building it that I had gone to soft on the rebound. I am not really sure of mid float and stack either 0.7mm would engage early on the 28 valves with a 12 rod but this is new to me.

The original HS just seemed to be more or less a stop with the 10 pivot and the 0.15, with this set up the clicker was very aggressive between 20 to 15. At 15 the fork would just sort of stall for a second before extending causing a tuck after turn in, even spinning the bike round at a stand still it could be felt. Also at 15 the ride starts to get chattery on the small stuff.

I think I will be very lucky if I have nailed it first time round but its a start.

Chris

cimwill · Mar 16, 2009

Tried it with the 0.44 and the old oil at 130 just to see, rebound is not right does not hold a line well and feels like it wants to wheelie of every thing . Open again I think I will add an other 14 and move the crossover back behind the deltas, it still dives a lot under hard braking so will also put the 18 back in the mid stack as Smorgasbord suggested.

Chris

bushmechanic · Mar 16, 2009

I would do this

Reb.
D20.1 x 2
14.1 or 16.1 or 18.1
D20.1x1
16.15
14.15
12.15
10x0.3 (or remove if still too soft)
14.25

if too stiff swap the 16.15 for a 17.1 or 18.1 and a 16.1

my logic is that with the bleed hole its softer initially so has to do more later to catch up

just an idea may not be particulary bright

thanks for letting us know how its going

Smorgasbord · Mar 30, 2009

Cimwill, how are you doing, any progress regarding the diving? Any bike would dive when using the front brake. But maybe yours is diving more and faster than expected?, so that it feels like your going to fly over the bars or something. Diving is slow speed compression, excessive clicker flow. Shut the compression clickers a few more clicks and try on smooth ground to find an acceptable dive reaction to braking.
The forks will now possibly be too harsh in the rough stuff in low speed compression. That can be softened, while retaining much of the the dive resistance, by adding a splitter shim, for your stack it could be something like this:

BV piston
24.1 x 5 <-------(This part now has more mobility up to a point and allows you to shut the compression clicker a bit more.)
14.1 <--------(This is the split shim added.)
24.1 x 5
23.1
22.1
21.1
20.1
19.1
18.1
17.1
16.1
14.1
12.1
9.5.3
16.25

The split shim can be moved up and down in the stack to change the characteristics of it.
This is only a wild guess of what might work, let's hope that some one have got a proven split stack for the 09 to show us.

Any thoughts, anyone?

cimwill · Mar 30, 2009

Well as of now I still have not tested with,my new 0.46 springs and a higher oil level, normal **** with the customs here, however I had a call this morning and I can now pick them up.

The diving was not the sort of thing that would put you over the bars, a lot of it I am thinking is in the geometry hence the addition of a shock spacer, I liked the feel this has given me on older KTM's.

The stock fork used a lot of it's stroke, no bad thing but if you are going down hill or braking going into heavily cross rutted ground it will bottom and be very uninspiring as the fork will already be low in the stroke, I think the stock low oil level, slightly soft springs and the heavy HS rebound stack were all part of this. I like to ride standing forward (I lead and the bike follows type of style) if you sit back on the bike and keep it in the power the stock setup works very well.

As for the new stack being to stiff, I do not think it will be, if I had more shims I would have added them, with the stock setup and clicker setting the bike was bobbing around I think I ended up at 13 to 15 out and it was still ridiculously soft and fluffy, you could start to get some feed back from trail trash if you go in on the rebound but the Comp clicker had little effect.
I think the change in mid valve piston diameter has a lot to do with it, I run 6 LS face shims and similar looking stack but without the odd numbers as it starts to tapper, in my 07 smoker and it is supple yet stands up well, all be it on a much lighter bike. I had thought as both have 12mm rods the results would be similar but it seem not to be the case, so from what I see now the older large dia. mid is doing a lot more work than the new 22mm mid .Does this make any sense to you or is it just the differences in the two bikes weights.

Chris

Smorgasbord · Mar 31, 2009

One reflection when looking at the oem -09 MV stack of your forks is that to get the same action as in the 28 mm cartridge the float should have been smaller, not just proportionally smaller but perhaps even smaller than that. I dont know really, its just a feeling... Maybe .4 or .5 mm intuitively... ? and no bleed shim in the MV!

Yes, throw in even more in the BV, as much as you can stand.

Maybe reduced MV float would help?

Regards

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