fork tuning for enduros

Taffy
fork is aprox. 5mm taller now its same length as KTM
if you stand 04 and 07 side by side footpeg to footpeg the 07 stands taller and front
axle is 15- 20mm forward of the 04
smorgy
I newer checked the swingarm mounting pos.
these changes is what the factory did for the works bikes Joakim talked about his frame
extended 15mm behind steering head and bjorne was 25mm
so long VIKING

viking

sounds like they extended the steering head by around 15mm plus the taller forks = 15-20mm longer wheelbase.

on 'the doc' we have a photo of the pre '04 and an '04 together. the '04 is 35-40mm shorter wheelbase due to steeper head angle. of course the headers rubbed the tyre and the shorter base must have made the handling 'interesting'!!

marko tarkalla was running a raised swingarm pivot three years ago by basically 'jacking' the rear and then fitting a lowered subframe.

i'm suprised that the swedish R & D weren't doing thie extended headstock back in '03 or '04. very slow....

thanks Per for the heads up on it.

regards

Taffy

Did the two Ø5mm holes to the sides at 170mm mod in the lower leg, as seen in Taffys "The Doc". This mod could be more of a spell than anything really useful. The gap between the upper leg and the lower leg is 0.5mm on the 2000 Ø43mm fork legs, as the upper leg bore is about Ø44mm. In theory the pressure/suction created by the lower leg movement would be depending of relative speed and of viscosity. How extended the fork leg is also a factor and the gap width would probably be a very strongly influential factor. If the fork leg is nearly totally extended the two mod holes would vent any pressure/suction very well. But when collapsed, the unvented bit is quite long and the two hole mod would be less effective. The thicker the oil, the more pressure/suction. I don't know wether the 3 bushings forks would benefit more from the 2 holes mod than the older Ø43's with 2 bushings? Since people do these two holes mods I have done it too, more as a matter of course than that I understand what actual benefit it would ever offer.
After beveling the edges of the holes, they were polished with a little cratex abrasive rubber wheel in the dremel and then fine polished with a little felt wheel and some flitz metal polish. They came out very nicely and with little effort and may with some luck not damage the seal. Maybe, when by mistake you are exposing the two holes outside the seal when working with the fork legs, they will it cause lots of oil spilling on your garage floor and soaking your pants too (fork oil, hopefully!) and cause a lot of foul language. Regards.

Re: fork rebuild

Taffy said:

i started testing two weeks ago and it's all still on going as i speak.

the first week i kept the shim stack the same and did four changes that i'd describe as 'free mods'.

1) i did the 17cm oil hole mod
2) i drilled the bottoming cones
3) i polished the cartridge rod
4) i machined the rebound tap to look like ZP3's

i kept everything else the same regardless. the forks were slightly plusher with a lot less spike. the midstroke change felt like it came from the drill mod whilst the spiking will be from the rebound tap.

one thing they don't tell you (although i found it in an old thread only last night) at k-talk is that if you do the drill mod you need an even bigger air gap because oil is filling each side of the chrome tube. the gap may be 125mm like viking says but with this mod it becomes 150mm i suspect. i shall know this sunday!

regards

Taffy

Click to expand...

well, this is what i found....

regards

Taffy

RE: Re: fork rebuild

i just want to bring you up to date on some stuff that i think is relevant here. i've been racing a katoom 520 from '02 for 3 from 4 weekends. i've been setting up the suspension for my mate.

i went straight to ZP3 front mod, drilled bottoming cones, the 34mm top-out springs, .46s and shim stacks to suit. these are 43mm forks so i'll be breif here. they need as little as 110mm air gap as per the book (i've written in the doc that this is 'bull') which the 48's on a huseyon't - more like 130mm.

anyway, the rear end!

well i fitted my old PDS8 (81/99) to it and it was better than his previous PDS2. good so far. i have the stronger PDS4 (85/111) on my bike and so really wanted to try it on the katoom next. alas it's all that's holding my bike up as the engine is out at present.

so i fitted the straight 95 which i'd bought for me! brand spanking and orange to boot! i broke it in last week, and even more so this week so there's a lesson there for us all! after no preload for last week i gave it a full turn for this week and another at the lunch interval. it's now about 245mm which is about it's optimum. new sags will be found after tonigh'ts wash.

anyway, it was very spikey last week but this week on a softer track it was lovely except on a couple of fast third gear corners, whap! whap! whap! with the throttle pinned.

being used to progressives it make you feel that you have too soft a spring fitted on the deeper hits and on hard throttle whilst cranked over a bit.

however i believe it needs the stepped needle that RT(?) in the USA are known for and is now fitted OEM i believe? the spring also makes the rebound ultra difficult to get right.

i'd like to try it on mine but my mate likes it coz it's orange!

if i do try it though i think i'd better get the needle....

it's also an interesting comaison: straight with the stepped needle v progressive and the std OEM needle?

regards

Taffy

Taffy, I was thinking of your two MV shims getting all the beating. Going a little bit overly philosophical here as well as lengthy, but please take a deep breath and dive in because I value your input. I've stuck to the subject anyway.
I like the idea of the MV stack acting like a gail-wrung umbrella, sparing tube, rim and yourself at the sharpest hits. But after having taken apart the CP of my 2000 OEM 43 mm fork and looked at the shims I'm concerned about the piston facing shim getting sucked out of shape at rebound.
If I get it right you are concerned about what the compression hits does to the shims.

The shims getting sucked through the piston ports.

Looking at the deformed shim from the OEM stack and holding it against the piston, you realize that it just can't seal until the pressure is high enough to force the shim to adapt to the port edges. The port suction causes a sealing problem as it deform the shim, even if it doesn't totally wreck the shim. Is this BTW the reason why some people prefer the stronger MV spring?, to iron out the port facing shim by spring force rather than letting the port suction do the job. Even if you don't know what is happening exactly, you might still feel the difference to form a preference?

There are only 3 ways that I can see.
Use a thicker shim facing the piston ports.
Use more and smaller ports in the piston to give better support at rebound.
Replace the fatigued MV shimming at every oil change, at least the port facing one.

If it true that the shim bending resistance is proportional to the cube of the thickness, then the equivalent of your 2 x 0.1 mm shims would be one single 0.126mm. There is hope to find such stock since it is very near.005"! It should be only 2% stiffer. 0.15 mm shims are then 3.4 times stiffer and could perhaps replace a 4 x 0.1 stack. Japanese 0.11 mm shims would then be 33% times stiffer, if you can find the same size that is, for instance you'd use 3 off of them to replace a 4 x 0.1 mm stack.
Of course a thicker shim would not take as much bending at sharp hit compression without damage. That is the back side of it.

It would be possible to add a wagon wheel "spoke" or two in every MV port and that would offer a lot better support for the poor MV face shim. One way would be to braze sheet metal spokes in there and then file off excess material and grind the whole thing flat again so that everything is at the same level. (Flat like a smorgasbord...) Additional spooks would increase oil flow resistance at sharp hit compression, but it may be that you would not notice the difference since there are other places of resistance that possibly are worse, or perhaps not?.

Considering how much is taken apart anyway and cleaned, it may not be such a chore nor expensive to replace the MV piston facing shim at every oil change. I have no idea how quickly the MV face shim deforms though. If it deforms at the first bump then the replacement might be in vain, at least regarding the sealing properties of the shim.


The strain of the shims at compression.

After having bent the shims several times over the zp3 like mod, it feels like the stack wants to Pringle crisp or saddle shape over the "zp3" rather than umbrella. Of course i could be wrong, but I don't think so and it's tempting to connect the piston to a compressed air hose somehow to verify. It feels emphatically that they will saddle and they have a lot of freedom and willingness to take that particular shape on the tap. Maybe at extremely hard pressure they would take the wrung umbrella shape but the risk is that it will get a lot of sharp bends if it does, perhaps not as sharply pleated as a traditional Scotsman's kilt, but you might know what I mean when you think of that gail-wrung umbrella. If you could control the radius of the saddle shape you could also use the shim material to its full potential.
Suppose that you used that single 0.127 mm shim as your MV. It could not bend to the same small radius as the two 0.1 mm shims that you use, not without breaking it. You'd have to restrict the bending radius of it, in the same way the reeds in 2-stroke intake are limited and for the same reason. It is not impossible that on the zp3 the radius will be on the safe side, but it would feel safer using a saddle shaped former to guarantee that the bending does not get too sharp anywhere on the shim. A former that the shims can bend around in a more controlled manner. It could either be the tap machined with the radius or, maybe easier to make, a washer or very thick shim carefully bent to radius and added to the MV stack and upon which the spring could act as a return spring for the whole package.
The stress on shims of different thickness calculated at two different bend angles and radius of former, it's just all theoretical of course but could serve as an indicator of what to expect:
Modulus of elasticity = 210000N/mm2. Length of curvature = 24 mm (shim diameter).
30 deg bend from mid to edge. Lift = 3.1 mm. Radius of former = 22.9 mm. End-end = 22.9 mm.
Thickness mm / material stress would not exceed
0.1 mm / 458.149 N/mm2
0.11 mm / 503.964 N/mm2
0.127 mm / 581.849 N/mm2
0.15 mm / 687.223 N/mm2

45 deg bend from mid to edge. Lift = 4.5 mm. Radius of former = 15.3 mm. End-end = 21.6 mm.
Thickness mm / material stress would not exceed
0.1 mm / 687.223 N/mm2
0.11 mm / 755.946 N/mm2
0.127 mm / 872.774 N/mm2
0.15 mm / 1030.84 N/mm2


60 deg bend from mid to edge. Lift = 5.7 mm. Radius of former = 11.5 mm. End-end = 19.9 mm.
Thickness mm / material stress would not exceed
0.1 mm / 916.298 N/mm2
0.11 mm / 1007.9278 N/mm2
0.127 mm / 1163.6985 N/mm2
0.15 mm / 1374.4470 N/mm2

Then how much strain can the shim material take? I have not a clue!

Regards

Smorgy

cheers for your in depth views and all the things you've said have at some point concerned me.

Dangeroo on k-talk has often harked on about shims being sucked through.

sorry to say though that the shim is supported at 5 'star' points and around the vast majority of the circumference. and the oil isn't being rammed through on rebound. what you have is oil sitting on top of the shim that is free to stay above the piston; (in your own time gentlemen please!' and the oil falls through at it's own speed. sure, the piston is hurtling up at the oil but as i say it's free to move up into the spring area if it can't 'fall through'.

also the proof of the pudding is in the eating and i have just done my friends forks after he raced for a day with no oil in one leg. all 4 x 24MV shims were fine. just one delta on the rebound had had enough. the first 24D. also would you believe the 4th or so shim in the compression stack - so work that one out!!!!!!

CV; 24, 24, 12, 24 (buckled) etc.

talk later, off to work and let you know the stack i've finished with in the 43s on this katoom.

regards

Taffy

well ktm lew helped me as did others on the orange side. haven't ridden it like this because i've got it ready to give back to it's owner. as i understand it we dopn't run 43s at all on husey's - correct?

the bike i finished 2/39 last sunday has since been revalved. it pogo'd on long rises and on chop it gave in too easily and couldn't keep up so more comp was needed.

the MV has changed from 24, 24, 18, 14 to 24, 24, 22, 20, 18, 15 and the rebound from 24d, 24d, 14, 24d, 20, 18, 16, 14, [email protected], [email protected] and added a 13 and then a 12 between the 14 and the 10. i also have gone from 1.3 float to 1.0 by removing tiny, tiny washers to the inside of the piston which i had made.

all adjusters set to 15 out from in. lew asked me to add a 16 into the MV for 18, 16, 14 but i don't have any so i igured i'd put 2 in for this time and one more could wait - but the 14 became a 15 to help a little. it has zero preload and this might go to 5mm sometime.

so that's it. might have to do more but we'll see!

regards

Taffy

Hi smorgasbord
I warned Taffy about MV shims getting sucked through piston port a thicker shim would
fix that but will hurt performance, solder a support bridge would fix that problem
solder in cast iron is tough and can fail
in 04 I had custom mid valve/rebound assembly which had a custom made piston to
address the problem with shim support knowing what know 12mm cartridge rod is
much better than the old 14mm rod in terms of performance
so long VIKING

Interesting things that you say, VIKING. If for instance you compared the 4 x 0.1 to the
3 x 0.11 CP stack, if the cube theory was true with these two CPs equally stiff, then there is more to it than shim stiffness when you use thicker shims. Could it be that thicker and fewer shims more easily are getting permanently deformed and that people actually can feel a difference in performance because of it? In that case the shim former would cure it, or is there even more to it that we don't understand? Yes, there must be.

It does not seem to be cast iron, gray iron would be more easily "carved" with a knife than this material seem to be. It could be some sort of investment cast steel or something. I think it will braze well, but the idea of something coming lose in there in case I'm wrong puts me off.

Taffy, I'm following your progress closely and with great interest.

Regards

smorgasbord
here is the skinny on shims a .11 shim is almost as fragile .10 the difference is negligible
you have to go up to a .15 to get durability problem is that .15 shim is stiffer than
two .10
problem that can be experience in mod piston port with bridge is that you are reducing
surface area of port which alters low speed and break away
I have to wipe the egg off my face I stated earlier in this post that 07 frame was extended well I measured last night 04 and 07 are identical from swingarm pivot to
fork axle and swingarm length the 07 frame is taller in order to fit the longer fork thats
the only difference that I could see
so long VIKING

Another free mod. Base valve check plate nuts drilled to help the weak conical spring shut the check valve faster by avoiding any suction cup effect. And to open full wide faster by reducing oil cushioning in nut head. Used a Ø2.5 mm drill for the holes. (Ø .1")

.15 shims are, if the qube theory is true, 3.4 times stiffer than .1 shims.
And the .11 ones are 33% stiffer than the .1, hardly negligible. The fragibility might be about the same though. I do not know, but if the .1 doesn't shatter but get out of shape, then the .11 wouldn't shatter either but might get less deformed thanks to the greater stiffness. Or is it the other way around? .125 might be the way to go, being twice as stiff as the .1 but just moderately thicker.
One weakness in using fewer but stiffer shims would be that any unflatness of a shim would be very dominant in the stack, while if there are many thin shims in the stack, the shim unflatness would average out to a great extent. The Ø12 rod BVs with their necessary thick stacks with lots of shims must be very good for stack flatness.
Then again if the MV shim facing the piston is a .1 doughnuting heavily, then a just slightly thicker face shim might be less bad even if it is not perfectly flat to start with either.

Regards

Taffy said:

sorry to say though that the shim is supported at 5 'star' points and around the vast majority of the circumference. and the oil isn't being rammed through on rebound. what you have is oil sitting on top of the shim that is free to stay above the piston; (in your own time gentlemen please!) and the oil falls through at it's own speed. sure, the piston is hurtling up at the oil but as i say it's free to move up into the spring area if it can't 'fall through'.

also the proof of the pudding is in the eating and i have just done my friends forks after he raced for a day with no oil in one leg. all 4 x 24MV shims were fine. just one delta on the rebound had had enough. the first 24D. also would you believe the 4th or so shim in the compression stack - so work that one out!!!!!!

CV; 24, 24, 12, 24 (buckled) etc.

regards

Taffy

Click to expand...

the best place to answer questions is to test and test again!

regards

taffy

Yes, indeed, we'll see how it works out. Regards.

Taffy said:

well it's taken 6 months of hard testing but i'm just about there now!

the result? SUBLIME!!!!

i changed the MV to that proposed by ZP3 from k-talk and that was as follows: 23, 23, 18, 13, 10-post seat. ZP3 post.

i kept the BV the same so that i could clearly define the changes made and their effect.

BV: 24, 16, 24, 22, 20, 18, 15, 11, [email protected]

i altered the float from 1.5 to a conservative 1.25mm by taking out the three home made shim spacers from each leg (read previous posts) fresh oil and then i set the level to 155cc and added the 30cc i'd found improved the bottoming out (i.e. stopped it!). i scotchbrited out alloy from the bushes as the shop is closed at the moment that is near me. one of the bigger bushes has a chunk out of it and i expected to see the fork seal also damaged - but it wasn't!

everything was set equally and then rebuilt.

as said. 155mm air gap then add 30cc and measure. this equaled 135mm when checked.

the forks didn't leak during this the most viscious of courses!
butts quarry IS A toughie!!!! it had jagged rocks, one foot tall were the norm, bolders - big *******s!!!!

the straights were slow and very, very rough. there were 3 motocross jumps and a drop over a 4' (yes 4' wall!) which had a 'facial' landing to a halt and turn left!

the forks absorbed everything faultlessly! i couldn't fault them on this terrain - fantastic! i need to thank ZP3 and all the crew at k-talk as well as viking here for their help. it's been hard work but it's been worth it.

i bottomed out twice when i got it slightly heavy on the front when landing so this wouldn't normally happen in an enduro. however this was a SLOW enduro and as i've learnt before, the faster you go the more suspension you use so i may have to alter it all a bit again. maybe some more oil taking the air gap to 125mm?

the rebound seems fine but again i may reflect on the difference between a slow track and a fast one.

one other thing. whilst the forks were split and on the bench i rebuilt them so far as getting the spring free length gap to the underside of the cap correct (see photo in the forks section of 'the doc'). the gap is 15mm with these .48s so i can either put 15mm of packing over them OR i can put longer top out springs in. by 'packing' them i raise the bike and slow the steering. by putting longer 'top-out' springs in i lower the front end and remove any slack when in mid-air.

the husey has 22mm top out springs but KTM have 37mm (i believe) which will virtualliy eliminate any slack.

so this will be the next thing i may try.

do later huseys have the same as katooms? around 35-37mm long?

regards

Taffy

Click to expand...

well i haven't ridden the mo-cheen since the above - july 23rd. felt good to be back i can tell you. i've been on a katoom 520 towards the end of the season and the 3/3 finishes helped me forget the blight of my gearbox woes.

i've quoted the above because i described the suspension as spot on really yet today i was testing my '04 frame for the first time. i put the original 22mm offset yokes back on and left everything else as was. back to standard low seat - not even a tall seat let alone my super tall one....!

it bottomed out a lot! it just wouldn't stop.

so that's the difference a frame makes!

had to put the comp in 12 on the front and even the rebound in 9.

plenty to do to it again to get it right.

regards

Taffy

Merry Xmas Taffy
I think that 03-06 chassi puts more weight on the front wheel that would explain your
woes raise the oil level and add some shims in the middle of the stack and run the
chain adjustment short and go out there and test the setup

have jolly Xmas Per

yes i was going to go from 23, 23, 18, 13 to 23, 23, 18, 15, 13. i will go to 125 air gap and also in an immediate test i will try 5mm of preload. i have the top out springs to fit as well. the rear wheel is in the middle of it's adjustment and at least i'm not getting through inner mud flaps now. a new chain is imminent and i want to try an extra link to lengthen the wheelbase, yes i know, more weight on the front again but i'll check wether the bike tracks well or not.

reading your posts, you said that the '07 frame is the same but that the forks are 5mm longer and therefore the front sits higher (front end kicked out)? is this right?

i need to ride on drier surfaces to make real improvements but that's what makes the bottom ing such a suprise!

merry xmas and regards

Taffy

Taffy
there is not enough holding power even with a 15mm shim you need at least 22or 20
to get some edge control on 24 shims that makes better mid speed control
the fork angle is the same one other thought on the weight on the front wheel the new
tank holds the fuel further back on the frame compared to the old tank that has to account for some of lighter feel of the 07

HAPPY NEW YEAR Per

hi smorgy

that drilled nut is standard on SX forks - but you knew that didn't you!

been and bought a load of shims from the importer today and done the forks.

this is what i've done:
i've gone to 23, 22, 20, 18, 16, 14 on the MV with a corresponding drop in the float from 1.25 to a corrected 1.1mm. i've fitted the taller top-out springs (34.5mm) and the clearance over the fork spring was 3mm so i settled on a 5mm spacer and therefore 2mm of preload at this point. i've also gone to 120mm air gap. for the rebound i have added a 19mm after the first round shim (a 20mm) to stop the deltas bending too far. one was buckled upon inspection as previously reported.

i get the feeling i've gone too far with the MV and may need to remove one and spread them out a bit.

we'll see.

as i'm starting to pop wheelies in first even when i don't want to now i'm going to go back to 50T rear and that will push the wheel back. a new chain with an extra link will take it even further so i'll have the SP on wheelbase issues i hope.

then we move to offset!

anyone tried husqy's eccentric wheel spindle? (via rekluse i believe).

regards

Taffy

Drop the float to .70...