Forks problem, no damping?

mikaels · Sep 14, 2008

Hello,

Last week I got the feeling that the forks don't work as they should.
I got the feeling that I have no grip and that the bike feels unstable in front and rear both. I am quite new in this business and would need some help to figure this out.

I decided to replace the oil too see if it would help. The oil in the forks had a rusty colour but all components looked good. This colour I have never seen before. I was surprised but thought that was moister/cracking causing the colour. The brand is Denicool and I have used it before. I put in new Motul, 140 mm as last time, and took a ride.

The forks seemed to be worse. I got the feeling of no or little damping but still not using the full stroke. I tried some different settings but no improvement of the handling. I even tried maximum return damping without feeling much difference.

I have taken the forks apart totally to check the components. The shims, springs and o-rings are all ok. Since I am not the only owner of the bike, is this the correct assembly of the piston?

I measured the rebound piston ring and it was similar as the new I have.
The inner aluminium tubes looked ok as well as the outer and inner fork tubes.
One of the Du-bushing 47 has a spot wear but very small. It is possible to see through the coating in two points of the size of 1x1 mm. All other du-bushings have a homogenous coating till the chamfer starts and you can see the brass material. Unfortunately, I have no useful photos of them.
Shall I replace all of them or only the one with wear?

The bushings in the screw sleeves are ok.
There are some small scratches on the piston rods. I can feel them with the fingers/nails.

Could this have an influence of the damping?

I have hard to understand why the damping is bad.
The only reason I can think of is internal leakage.
Could it be the inner aluminium tub which is outside the tolerances?
Does any one know what the tolerances are?
If it is the rebound piston ring I am confused since it has similar dimension as the new.

Any ideas of how to go on with this case?

Thanks for the help in advance.

ktmlew · Sep 14, 2008

mikaels said:
Hello,

Last week I got the feeling that the forks don't work as they should.
I got the feeling that I have no grip and that the bike feels unstable in front and rear both. I am quite new in this business and would need some help to figure this out.

I decided to replace the oil too see if it would help. The oil in the forks had a rusty colour but all components looked good. This colour I have never seen before. I was surprised but thought that was moister/cracking causing the colour. The brand is Denicool and I have used it before. I put in new Motul, 140 mm as last time, and took a ride.

The forks seemed to be worse. I got the feeling of no or little damping but still not using the full stroke. I tried some different settings but no improvement of the handling. I even tried maximum return damping without feeling much difference.

I have taken the forks apart totally to check the components. The shims, springs and o-rings are all ok. Since I am not the only owner of the bike, is this the correct assembly of the piston?

I measured the rebound piston ring and it was similar as the new I have.
The inner aluminium tubes looked ok as well as the outer and inner fork tubes.
One of the Du-bushing 47 has a spot wear but very small. It is possible to see through the coating in two points of the size of 1x1 mm. All other du-bushings have a homogenous coating till the chamfer starts and you can see the brass material. Unfortunately, I have no useful photos of them.
Shall I replace all of them or only the one with wear?

The bushings in the screw sleeves are ok.
There are some small scratches on the piston rods. I can feel them with the fingers/nails.

Could this have an influence of the damping?

I have hard to understand why the damping is bad.
The only reason I can think of is internal leakage.
Could it be the inner aluminium tub which is outside the tolerances?
Does any one know what the tolerances are?
If it is the rebound piston ring I am confused since it has similar dimension as the new.

Any ideas of how to go on with this case?

Thanks for the help in advance.

Would be nice to know what bike you are working on...I suspect you have some severely cupped mid-valve shims...need to remove all shims and inspect for cupping or cracks. The 24x.10 shim beside the piston in this picture shows evidence of cupping.

ktmlew · Sep 14, 2008

Also need to add that base-valve stack looks REALLY soft and harsh at the same time...

bushmechanic · Sep 15, 2008

http://www.husaberg.org/index.php?name= ... &start=165

second to last post has some BV stacks and MV configurations that should be an improvement

if the MV shims are ok and the little spring on the MV is OK (you can see it in lews picture)

and the check plate on the BV, ( thick shim under the BV nut) is not warped and is sealing off OK

then check that the rebound shims (delta shaped) are covering their ports correctly

sometimes its possible that the spring guides/ fork caps/ fork rod are not put together

properly and the rebound adjusters are not working.

the rod has to bottom out inside the fork cap on assembly.

thicker oil or more oil will make the forks stiffer.

could you possibly list the shim stacks for us? the MV float dimension and spring strength/prelaod are important too.

everything looks OK except the strange BV shimming, perhaps the MV set up is also strange?

regards
Bushie

mikaels · Sep 17, 2008

It is a FE501e -02.

The shim stacks are almost original.
Shims comp: 18*.2; 11*.2; 14*.1; 16*.1; 18*.1; 22*.1; 22*.1; 20*.1; 24*.1
Return: 4x24*.1 piston 2x24*.1 Delta; 14*.1; 22*.1 Delta; 20*.1;
18*.1; 16*.1; 14*.1; 10*.3; 16*.25

All components look good and that makes me a little confused.
I know that some have got problem with their fork springs. The spring could touch the hydraulic stop but I don't know how to detect or if that could cause my problem.
The only thing I saw was that the piston rod is not completely straight.
I noticed that when I was rotating the piston rod and saw a small movement at the hydraulic stop top.

Does any one know the tolerances of the inner aluminium tube? 28mm something.
If wear, the oil will pass the rebound valve in both directions without any damping effect.

ktmlew · Sep 17, 2008

mikaels said:
It is a FE501e -02.

All components look good and that makes me a little confused.
I know that some have got problem with their fork springs. The spring could touch the hydraulic stop but I don't know how to detect or if that could cause my problem.
The only thing I saw was that the piston rod is not completely straight.
I noticed that when I was rotating the piston rod and saw a small movement at the hydraulic stop top.

Does any one know the tolerances of the inner aluminium tube? 28mm something.
If wear, the oil will pass the rebound valve in both directions without any damping effect.

Not sure what yopu mean in the (red) question above? Some of the higher rate .48 and above, springs WILL sometimes rub the S-G but you can sand the guides down for clearance?

OK...I need to format this so I can read it...

Base=valve stack really, really, really soft!!!
24x.1-add (3)
22x.1<remove (1)
20x.1
18x.1
16x.1
14x.1
11x.2
18*.2

Rebound
(2)24Dx.1-add (1) here for atotal of (3) and another under the next shim
14x.1<change to 16x.10>
24Dx.1<add this shim>
20x.1
18x.1
16x.1
14x.1
12x.1<add this shim>
10x.3
16x.25

Mid-valve <was check-plate (4)24x.1>
(3)24x.10
20x.10
14x.10
10x.20
13x.10
16x.1
(2)20x.10
10x.10 or 10x.20 (?) use as many as needed to get float, to around 1.10mm.
ck-spring

Oil height 140. Fill to top and let perk, stroke rod until fully damped in rebound (return). Fill to top again but DO NOT pour oil into cartridge rod or it will leak out rebound knobs. Let set for 5 minutes. Suck fluid down to 140mm.

The Rebound Delta shims MUST cover the small triangular ports in the rebound piston.

Float can be checked by building mid-valve stack on stem w/o ck-spring, put piston on and either measure gap between piston and shims or add shims until the gap is filled, them measure extra shims?

Set comp & rebound clickers to 16 out.

This won't be the perfect set-up but will be a pretty darned good start. If it doesn't have any damping, then you have something assembled incorrectly...

ktmlew · Sep 17, 2008

http://www.husaberg.org/modules/gallery ... g_cone.jpg

You don't have to remove the bottoming cone to access the reb/mid-valve. Just clamp the cartridge rod below the spring-guide and unscrew the spring-guide from the rod same as removing the cap. Then the cartridge rod will drop out the bottom.

You get the cartridge rod bushings and piston bands with a PivotWorks fork rebuild kit...

ktmlew · Sep 27, 2008

Ummmm? You still alive?

mikaels · Oct 12, 2008

I am alive but confused.
I can only do the tests on Saturdays when the track is open so it takes some time to see if there are any improvements.

Last time I had a problem with the fork, the damping was gone.
I replaced the inner bushings and o-rings.
The performance was ok after that.
Due to this, I thought the old problem was back but now I think it is something different.

I have now replaced the springs to the old 4.2 N/mm and new 47 mm du-bushings, waited 14 days to get the bushings.
I have decreased the rebound and compression damping very much but I still not use the whole travel.

When I hit a stone or a root, the wheel will jump to the side.
I thought I used too stiff springs but yesterday, with the old softer springs in, it was no difference. This makes me confused.
All bumps are transferred to the handlebar.
The ride is so harsh that it is impossible to go with higher speed.

Today I got an idea, the friction in the dust wiper and the oil seal is too high.
Could that cause the behaviour?
Any ideas of what tests to perform?

When the forks work properly, I will start to test new shim configurations.

ktmlew · Oct 12, 2008

The valving IS the problem...it blows through the travel so quick it bounces off the bottoming cones plus the rebound is so softly valved it can't control the spring. You also should update the top-out springs to the 05 part before they explode and tear up everything...

bushmechanic · Oct 12, 2008

I have decreased the rebound and compression damping very much but I still not use the whole travel.

ahm maybe if your curiuous just for fun if you havent allready perhaps put the forks together without the springs and bottom them out to
check where full travel really is.

sometimes setting up the forks to use all the travel makes them really harsh
because they are so soft that they ride too far into the stroke and rest on the springs
might be an idea to try and set them up to be plush initially and ride higher in the stroke to float over the rocks

if initial harshness and deflection are the problems I would try to fix those things first with the valving but its not my bike...........

about 80% of bikes I watch at the MX track have stock valving or homebrew softer than stock and the owners have tried to set them up
to "bottom once a lap"
most of them want steering dampers because of initial harshness and deflection. "but I took out so many shims" they say.
try adding more shims ? just a thought

I'm not saying that your forks are actually working properly mechanically...
there is no way I could tell that without riding your bike.

whats interesting is that it seems the forks were fine with the current valving right?

and then they got worse with the same valving and worse again when you changed the oil ?

if thats what happened and they are put together right with no dammaged shims etc I have no idea as to the problem but I hope you can
get it sorted out.

regards
Bushie

edit

perhaps oil breakdown made it too thin to work with the soft stacks

and the new oil was even thinner ?

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