Yoken

~SPONSOR~
Oct 18, 2001
56
0
Hi fellow enthusiasts,

Could someone post the detailed stock shim stacks for the fork of the 05 CRF450 ?

- Base valve comp and reb stacks,
- Mid-valve float, comp and reb stacks.

Although the bike handles well in stock form, it bottoms out pretty easily on big jumps and charging through breaking bumps on lap 5 makes me feel really old (...maybe I am?).

I'm just curious to try a couple different shim stacks on my own and see how it goes. I'll give myself 2 to 3 trials. If it fails, I'll ship the forks to a professional tuner.

Thanks,
Yoken
 

Yoken

~SPONSOR~
Oct 18, 2001
56
0
Kawamaha,
I had a look at your link and like the idea of re-drilling the clutch perch for an easier pull. I heard about it but never saw a sketch. Thanks for sharing that with us. Although the Honda clutch is pretty good, I'll give it a try. I finally took the fork apart. Here are the specs I found :

BASE VALVE (id=6mm)
(from the bottom to the nut)
At this point I already have a question. The base of the stem is shaped like a cup and is drilled with 6 small holes. Those holes communicate with the exhaust ports of the needle circuit (LSC clickers). That "cup" is topped with what looks like a small/stiff valve stack
10 x 16.1
15.1
14.1
13.1
12.1
11.1
16.2
I can't figure out what it does. Any ideas?
The above stack is then followed by a stiff "base plate"
6x30.5x2mm
then a more standard (rather thick) single stage stack
18.1
19.1
20.1
21.1
22.1
23.1
24.1
25.1
26.1
27.1
28.1
29.1
16x30.1
PISTON
check plate 8.1x30.5x4.5mm
spring
cup washer
nut.

MID-VALVE FLOAT
Because of the fairly soft shim stack, it was quite difficult to measure it accurately with a feeler gauge. So I calculated it by measuring the thickness of the different components and found : 0.25mm (which feels about right with the feeler gauges)

MID-VALVE STACKS
(from the bottom to the nut)
Cup washer and spring
id6xod10x0.2mm spacer
id6xod10x0.2mm spacer
id6xod5x0.2mm spacer
id6xod8x2.25mm collar (on which the shim stack "floats")
COMPRESSION STACK (id=8mm)
4x17.1
6x20.1
PISTON
REBOUND STACK (id=6mm)
20.1
20.1
18.1
12.1 cross-over
16.1
15.1
14.1
13.1
12.1
11.2
3x16.3 spacers
washer 17x2.5mm
nut.

That reminds me a bit the WP setup of my old '02 KTM520. I think that the mid-valve float is a bit too large and causes the damping to come into play too late and/or at too high speed. To compensate, the base valve compression stack seems to be build quite stiff. This, added to a high oil level, is probably why the fork feels so stiff in breaking bumps.

So basically, I am thinking to :
- reduce the mid-valve float (0.15mm?),
- change the mid-valve compression stack to something more like
20.1
19.1
18.1 ...
- lighten the base valve compression damping. Something like
4x30.1
29.1
28.1 ...
- reduce oil level.

What do you think ?
Yoken
 

KTM-Lew

Member
Jan 26, 2002
428
0
MID-VALVE STACKS
(from the bottom to the nut)
Cup washer and spring
id6xod10x0.2mm spacer
id6xod10x0.2mm spacer
id6xod5x0.2mm spacer
id6xod8x2.25mm collar (on which the shim stack "floats")
COMPRESSION STACK (id=8mm)
4x17.1
6x20.1
PISTON

What does the "check-spring" push against & what is the ID & OD of the spring? The Twin-Chambers I've had apart didn't have a "check-spring" to close the floating shims but they were earlier models?

I'm assuming it pushes against the 17x.10?
 

KTM-Lew

Member
Jan 26, 2002
428
0
So have they lengthened the tap to allow room for the cup? Hmmmm? I guess since they always had those long post spacers there was enough room? Vedddyyy int er esting
 

russ17

Member
Aug 27, 2002
301
0
The showas doesn't have the cup like the KYB it's more like a base plate that has a groove in it. the spring rest in the groove on the base and pushes against the 17.1. In order to change the float you need to either add or subtract shims. or change the height of the collar. Of coarse this is dependent on the build and the amount of float you desire.
 

Yoken

~SPONSOR~
Oct 18, 2001
56
0
Marcus,
You're right, 0.25mm float is not too large. I went back to my notes and the float on my old KTM was around 1.25mm... (I should've read my notes before posting. Sorry).
However, I've see floats of about 0.1 to 0.15mm working fairly well with MV shim stacks like 20.1 - 19.1 - 18.1 - 16.1 - 14.1 - 12.1 - 10.1. My problem is that I don't know what base valve was associated with it. I'll have to make my own experience.
How would you compare the above stack versus the stock 6x20.1 - 4x17.1 ? Stiffer or softer ?

KTM-Lew,
I'll try to get you a pic of the MV as soon as I figure out how to link it to this site. Russ17 made a good description though. For info, the spring is ID13.5xOD14.5mm. It sits in the groove and pushes on the 17.1.

My goal is to get :
- more plushness in braking bumps,
- a bit more fork dive at the entrance of a corner (spring rate? preload? bleed circuit valving?),
- while maintaining stock bottoming resistance (getting a bit more would even be better)

...am going to think about it a bit more before I start messing things up.
Yoken
 

russ17

Member
Aug 27, 2002
301
0
Yoken said:
Hi fellow enthusiasts,

Although the bike handles well in stock form, it bottoms out pretty easily on big jumps and charging through breaking bumps on lap 5 makes me feel really old (...maybe I am?).



Thanks,
Yoken


your weight and ability could be helpful.
 

Yoken

~SPONSOR~
Oct 18, 2001
56
0
5ft11 (1m80) - 205lbs (93kg) with gear - Turning 36 next week.
B rider when the gate drops... C after 3 laps... and S (Soar) the next day... that fork is killing me!

Rear sag was set at 100mm. I haven't checked the front end though but the bike felt well balanced in stock form. Fork oil level was stock too (but not measured). The bike felt great the first time I took it out. It was on a smooth hardpacked amateur supercross-type track. Then my joy disappeared when I hit a fast MX track...

The stock springs should be about right for me. However, somebody mentioned that the fork spring pre-load was a bit on the high side and that he had positive results when backing it off 3 to 5mm. I'd like to check that out. I've always liked to have "stiff" springs with low pre-load on my previous bikes.
Thanks for your input,
Yoken
 

marcusgunby

LIFETIME SPONSOR
Jan 9, 2000
6,450
2
Yoken i would never go on this board and try to claim to know which stack is stiffer or softer, once you alter the float its very hard to compare, ive seen a few showa mid valves, and the ones on my 04 rm125 wanst nice with a stiff stack and more float(0.2mm i think) IMO a softer stack with less float(must be 0.1mm to be easily changed) works nicer.

I will admit i have not changed the mids much on the showas, i do know many claim it needs doing, but they are not a bad fork with just a base valve shim change.
 

Yoken

~SPONSOR~
Oct 18, 2001
56
0
KTM-Lew,
As promised, here is a pic of the MV base plate (1st trial. I've never made any attachments before...)
 

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Yoken

~SPONSOR~
Oct 18, 2001
56
0
Marcus,
I agree with you. The stock Showa is not a bad fork at all. It's in fact the best I've tried so far. The Kayaba of my old 99KX250 and the WP of the 02KTM520SX were far worst in stock form, IMO. However, by just softening the BV I'm afraid to have bottoming issues. I'm not a talented rider and I do land heavily quite often...

I've just checked the fork spring pre-load : 6mm! That doesn't seem excessive too me. I could back it off 3mm, but I don't think it is going to help much in breaking bumps though.

Please see attached pics. Is this what you've called in earlier posts "a shim stack on the bleed circuit" ?
I really don't understand how this works. How could the oil have enough pressure behind the needle to flow through those 6 ports and deflect the shim stack? The 2 exhaust ports of the needle circuit should be more restrictive for that to happen.
Plus, what's the point of having a shim stack in series behind a needle?... I feel a bit stupid to ask, but that thing has been driving me nuts for two days!
 

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kawamaha

Member
Mar 16, 2005
179
0
this is for the compression adjuster. first it's a check valve so it does not influence the rebound damping when you change the compression clickers. you ask "How could the oil have enough pressure behind the needle to flow through those 6 ports and deflect the shim stack". Of course it has enough pressure. it is only a small amount of oil (the needle is just for low speed compression) so the shims need to open very little.
but for me it is more a gimmick than a serious thing ;)
 

russ17

Member
Aug 27, 2002
301
0
try a set of .49 k/g first and start eliminating some of the 16.1's from the bleed stack. Then play with the base. This will give you a better idea of what the changes will feel like.

Russ
 

marcusgunby

LIFETIME SPONSOR
Jan 9, 2000
6,450
2
Yoken you really have 2 extremes of forks listed, the 99kx250 has a mid valve with no real lift and plenty of damping, the ktm is the opposite, it has alot of mid life and no real shim stack strenght, yet you notice both are bad forks, so this tells us we need the correct amount of damping, too little or much is bad, the advice given by russ etc will really help, i used to think every fork needed major work to get it perfect for me, then after about 5 tries on the kxf it was a stack very close to std that was the best.
 

bclapham

LIFETIME SPONSOR
Nov 5, 2001
4,340
0
i would tune with just the base valve on that fork. a big bike like a 450, if you take out too many shims its gonna ride too low and feel worse. Plus, its more likely gonna bite ya.
 

Yoken

~SPONSOR~
Oct 18, 2001
56
0
Thanks for your input guys!

Kawamaha, "gimmick" is exactly what I had in mind but I just didn't dare to mention it... I'd be curious to see how a bleed stack shows on a dyno though, if it does.

Russ17, you are the 2nd person to tell me to go stiffer on the springs. Interesting and quite confusing. I am not sure if I am fast/aggressive enough to use stiffer fork springs. With current springs, the bike won't turn unless I stay on the front break and sit on the gas cap! So I'm afraid to go stiffer at this stage. But I'll follow your (and Marcus') advise and will start by softening the BV stack and move from there.

For info, I put the fork back together on Friday and went riding yesterday. You can check a couple pics of the track at www.jbmotocross.com. That will give you an idea. Unfortunately, it was not a high speed MX track so I could not test the breaking bump issues... but here is what I tested :

FORK
Fork height: base of the fork cap 7mm above clamps
cartridge oil: Bel-Ray 5W
Valving: Unchanged (stock)
Spring pre-load: reduced from 6 to 3mm
Oil volume: 350cc ATF (stock std setting is around 382cc)
LSR 6 out
LSC 10 out
Dunlop 742F @12PSI

SHOCK
LSR 8 out
LSC 10 out
HSC full out
SAG 100mm
The rest (oil, N2pressure, valving,...) is stock
Dunlop 756 @12PSI

The bike handled pretty well. I had less vibration in the bars on small accelerating bumps (locals call those hardpacked bumps "riding over a wash-board"...). The fork didn't feel like diving more than before under hard braking (I guess because of the stiff BV stack). I still had to sit on the gas cap to turn but the front tire felt more planted throughout the turn.

Front and rear bottomed out a couple times when over-jumping the tables or hitting the face of a jump too fast and off the gas, but surprisingly it wasn't a bone-breaking experience...

So now I'm going to order some shims and will get back to you guys with some more test results... tuning is just as fun as riding!
 

Yoken

~SPONSOR~
Oct 18, 2001
56
0
Bclapham... I'm afraid I've been bitten already. Went down 6 times in 2 months! Fortunately with only bruises and scratches... you see I can land on my head even without messing up with suspension settings! Thanks for your concern though. I'll definitely go step by step and won't charge to the 1st turn before I get a good feel of what's going on.
 

bclapham

LIFETIME SPONSOR
Nov 5, 2001
4,340
0
the important thing we found for cornering was the rear spring. with a 200lbs pro on board, the rear would squat comming out of corners on hard accel, even tho the spring has the right sag numbers. we went to the next spring up and it was better- made the rear end a bit higher.
 

marcusgunby

LIFETIME SPONSOR
Jan 9, 2000
6,450
2
I too have found a 4 stroke will just not work well with a soft shock spring, it ruins turning and balance, i can go down a little on the forks spring rate.

How did you reduce preload on the springs, maybe it sounds like a little less(maybe 1mm preload) will work for you, you could also expriment with different ics springs-however with so many variables its easy to get confused.
 


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