Evolution suspension did a similar conversion on my Multi with great results. Totally changed the character of the bike.

 

Howdo!

Be interested to see how you get on

Totally agree with you, the K5 forks are a good piece of kit on the road, I've got loads of confidence in mine. If this feel can be transferred to the SS forks I would be impressed.

Best of luck Pablo

 

I have the forks together. The gsx-r spring diameter is too big for the ss fork tubes (38mm and the fork tube internal dia is 37mm). The length of the 900-ss springs (I have race-tech 0.85kg/mm, the same rate as the gsx-r stock springs) is 340mm. They fit to the gsx-r cartridges but require only 10mm spacers to get 15mm preload. The hydraulic stop rings on the gsx-r cartridges will rub on the inside of the 900-ss springs, so I removed those (race-tech recommends removing them anyway when re-valving forks, so I dont believe it is an issue as long as you keep enough comp damping to prevent bottoming).

I had a test ride and I think the forks now feel a lot like the gsx-r. They seem to just swallow most of the bumps and still feel settled enough.

The modification really requires aftermarket aftermarket springs, the stock gsx-r springs are linear 0.85kg/mm but wont fit to the 900-ss forks. The stock 900-ss springs are about 0.6kg/mm (I measured it with a scale and progressive, the rate changes to about 0.9kg/mm at roughly 70mm of travel). I wouldn't try this conversion with the stock 900-ss springs.

 

I was thinking about sticking the whole forks from a late GSXR in to my SS. I think they use the same diameter yoke so should slot in. Not sure about front wheel though.

Would be great if you could do a full picture report on the fork build, this sounds like a great cheap-ish upgrade

 

I have now disassembled a pair of cartridges from K0-3 gsx-r 750 and they seem to be better built than the k4-5 cartridges.

pics here:

https://picasaweb.google.com/102766334876883285574/Gsxr750K2Forks#

The reason I did this was that I found out that there still is a design fault in the rebound circuit of the k4-5 forks, might be easily fixed, but if someone is planning this mod, the K0-3 are the cartridges to get.

reasons:
- the bleed circuit on them are flawless
- the bottom cup washer diameter is the same as on 900ss, so no need to leave it out

More on that later, when I have tried them on my forks.

 

Well, the K2 internals went into my forks today and they fit without any modifications, as long as you have the fork caps from the gsx-r.

No spacers at all, just the metal washer over the 900ss spring gives 10mm preload.

If you want to keep stock looks, use the 900 ss fork caps and preload adjusters, but the center part the damper rod screws into must come from the gsx-r because the damper rod diameter is 12 versus 10 mm. You can use the 900 ss rebound adjuster screws, but the part below the threads must be cut off to work with the gsx-r rebound adjuster rods.

With the k0-3 internals, the cartridge bottom to fork cap distance is exactly the same as on the 900 ss internals, so the fork length doesn't change.

 

I kept the GSXR fork caps when I did mine. I thought they were a little nicer looking. What oil level are you using ?

 

120mm. I also added 4 17x.15mm shims to the rebound stack. The comp stack is stock. The damping should be now comparable to race tech c34 and r18 stacks.

Oil is 5w

Race tech stacks

http://www.mahonkin.com/~milktree/re-shim-project/racetech-shim-stacks.html

 

pajazo, thanks again for the help with my SportClassic Marzocchis!

You mentioned you did Shim Restackor calculations on the stock stacks... and that the stock GSXR piston port-size different from Gold Valve made the RaceTech shim setups too stiff. (Not enough "flow".) You also said the K5 GSXR shim stack was too stiff as well, and the K3 was a lot softer.

Could you share those calculations here?

Also, how should I modify my (K5 shim stack/GSXR-showa piston) to be the equivalent of a (RaceTech C34 stack/ "gold valve" piston) in terms of your stiffness calculations? You said how to fix a K3, not a K5.

Or can I just work off the picture you took of a disassembled stack? (I think K3/K5 share same base shims, only top is different.)

In a K5, I also found 100mm air gap was a bit too much... the fork will never get full travel. I think 120mm may work better, some GSXR people say the same thing. I will have to remove my fork from the bike to do this... or do volume calculation, unload front forks, and remove oil volume via syringe.

RaceTech recommends leaving the physical stop in but disabling it by drilling hole at bottom of "bucket". I compromised and drilled a <3mm hole 1/2 way down.

Finally, you are right -- on the K5, I can screw in the compression screw, but as long as there is even a LITTLE bit of rebound open, the fork will not lock up compression. If I screw rebound in, the fork WILL lock up compression.

There is something going on with that bleed hole at the top. I think the K5 is indeed a hybrid internal-external bleed, and this "flaw" you mention is actually a forced-minimum value for compression/bypass.

What has your investigation revealed?

 

Just rode 100km of bumpy countryside twisties. Now when I have the fork settings dialed in, I feel the first time that I have a fork setup that is doing the same things as the öhlins shock in the rear.

My settings are comp 4 clicks out, rebound 1 turn out.

An oil level of 100mm is very high. Race tech recommends 120mm with the ducati forks. I'm using 0.85 kg/mm 900 ss springs from race tech.

I would not say that the showa pistons don't have enough "flow". The port size is large enough to absorb fast bumps without harshness. The port size just has an effect of the deflection of the shim stack with a given pressure, so the shim stack needs to be matched to the valve port size and number, you can't just copy a shim stack and use it with a different valve with the same results.

If you want to match the C34/R18 stack stiffness (and k2 comp stack), remove 4 17x.1 and one 16x.1 shim from the k5 comp stack. I suggest to leave the rebound stack as is. I made an error with the k5 rebound stack in the previous calculations I pm'd you. The K5 rebound stack is pretty stiff as is and very close to the R18.

Keep in mind that the port dimensions are measured from the pics on Peter Verdone's site, I don't have gold valves to measure. And the port dimension inputs in Restackor don't take into account different port shapes (sector/round) so this is really an approximation.

I guess I'll take apart a K5 cartridge now I have them lying around to find out how the rebound circuit on them really works. I'll post pics when I have the time to do it.

 

Here's the shims I had in my K4-5 cartridges, check that you have the same before modifications

k4-5 750 showa comp
17x0.10x5
16x0.10x4
15x0.10x2
14x0.15
13x0.15
12x0.15
11x0.15
8.5x0.20x2
11.5x0.40

rebound
17x0.10x5
17x0.15
16x0.15x2
15x0.15
14x0.15
13x0.15
9.5x0.20x2
11.5x0.40x2

 

Hm.... mine seem to be different. This is really concerning.

Link to my compression stack teardown (05 GSXR 600/750)​

Do K5 GSXR-600/750 have different setups? I need to speak with the person I bought my forks from.

What shim stack did you use in your calculation?

k4-5 750 showa comp

[Yours]		[Mine]

17x0.10x5	17x0.10x10
16x0.10x4	
15x0.10x2	15x0.10
14x0.15		14x0.15
13x0.15		13x0.15
12x0.15		12x0.15
11x0.15		11x0.15
8.5x0.20x2	8.5x0.20
11.5x0.40	11.5x.04

 

Your original stack calculates about 12% stiffer than mine with restackor.

I can not be sure that the one I had wasn't already modified but I think it's unlikely. Maybe there are differences between the year models or 600/750 models.

 

https://picasaweb.google.com/102766334876883285574/GsxR750K5Cartridges

The K5 cartridges have a loose fit of the rebound adjuster needle shaft to the rebound valve holder bore. The bore diameter is 4.49 mm and the needle shaft is 4.32 mm. This leaves about 1.2 square millimeters of gap for the oil to leak out of the cartridge during rebound and compression strokes. Compare that to the 1.3 mm compression bleed hole (1.5mm2) race tech specifies for gold valve applications for some non-adjustable forks. This explains why I needed 0 to 1 click open comp setting on these cartridges to get enough compression damping.

The K2 cartridge is otherwise similar in design but it has a non-existent gap between those parts, the fit is air-tight.

Plugging the "weep hole" in the fork cap would prevent the leak but leave some air trapped inside the damper rod. I'm not sure if that would have a noticeable effect on the damping function.

 

if you go to Suzuki Motorcycle OEM Parts, Babbitts Suzuki Parts House you can check the oem part #. the 2003 600 and 750 cartridges are different #.

2003 Suzuki GSX-R600 FRONT DAMPER | Babbitts Suzuki Parts House

2003 Suzuki GSX-R750 FRONT DAMPER | Babbitts Suzuki Parts House

 

Valving

We use to install Showa cartridges in mid 90's 900/750's all the time. The trick for those was machining the lowers for compression adjusters...lol

Please also remember that the washer below the clamping shim is not always flat, and this causes abnormal damping. One area which you might check is the preload on the check washer, and also to ensure the washer is not grooved. It is important to make sure it seals.

100mm will not work. I do not know your weight, bu .85's are in the ballpark for a lighter rider, however a fluid height of 100mm will not give the proper feel at the transition of trail braking to full lean. However, this appears to be a street ridden unit, so you may not feel it...

It is common to have one leg slightly longer than the other due to machining and also the different cartridges. It is then important to set the ride height with one leg and alter the other slightly higher or lower to ensure the axle slides through smoothly. Then before tightening the pinch bolts, bounce it up and down to be certain everything settles in. Since you seem to understand the rest of it, I would imagine you already know these simple items.

Good Luck,


Thor

 

100mm will not work. I do not know your weight, bu .85's are in the ballpark for a lighter rider, however a fluid height of 100mm will not give the proper feel at the transition of trail braking to full lean. However, this appears to be a street ridden unit, so you may not feel it...

Thank you , Thor. Are your recommendations for "spring in" or "spring out" when doing oil level?

The 2005 K5 GSXR 600 shop manual (PDF) gives bad instructions (100mm spring out)... or perhaps that only applies for the (longer) GSXR stock upper.

I weigh 150lbs/68kilo without gear. In order to remove 20mm of oil without removing the forks from the bike, I need to do some math:

GSXR damper rod OD:	12mm
Showa damper rod OD:	10mm

			Marzocchi SC	Showa 748
Lower ID:		40 mm		(40mm??)

Lower OD:		43 mm		43mm
Bushing notch:		42 mm		(42mm??)
Bushing thick (x2):	1 mm		1.5mm

Upper ID:		44 mm		(45mm??)

pi * [ (44 mm)^2 - (43 mm) ^2 + (40 mm)^2 - (12 mm)^2] / 4 * -20mm in cc = 24.24 cc

Assuming when fully compressed the fluid fills the gaps between (the upper and the lower) and (the lower and the rod), I need to remove 24.24 cc using a syringe and PVC tube. This will save me having to remove the forks from the bike.
(I will need to measure and account for the inner volume of however long PVC tube I use.)

Bradblack did something similar and MEASURED 27cc per 20mm for Showas.

Likely scenario: pi * [ (45 mm)^2 - (43 mm) ^2 + (40 mm)^2 - (10 mm)^2] / 4 * -20mm in cc = 26.33 cc
Works out perfectly.​

I have a photo of the compressed cartridge showing the fluid will not expose the top of the cartridge proper even at 120mm.

Your original stack calculates about 12% stiffer than mine with restackor.

I can not be sure that the one I had wasn't already modified but I think it's unlikely. Maybe there are differences between the year models or 600/750 models.

I think you are correct. I contacted my seller. Mine came off a 2004 GSXR 600. They were likely not modified... my stack holders showed no signs of marring/tampering (until I did ).

 

i'd be running them much lower than 100. probably 140 or so. the difference it makes is in the last 1/3 of travel

 

You can use this trick to remove the springs with the cartridges in bike.
https://picasaweb.google.com/102766334876883285574/GsxR750K5Cartridges#6043966198319013394
https://picasaweb.google.com/102766334876883285574/GsxR750K5Cartridges#6043966280730280226

Putting the spring back is easy, you dont need to compress the spring much, threading in the cap will compress it.

 

Could you check the permissions on the links in your last post? They do not work.

Edit: Check that, I found them in the normal album, the mobile link was the issue.

https://picasaweb.google.com/102766334876883285574/GsxR750K5Cartridges#6043966198319013394
https://picasaweb.google.com/102766334876883285574/GsxR750K5Cartridges#6043966280730280226

Great idea! But, I thought you have to unload the front forks to unscrew the caps safely? And the oil level needs to be measured when vertical.

A trip to my mechanic may be in order. I do not have a center stand, or front-triple floor stand.

 

I have 2 sets of GSXR cartridges:

The first I bought are reportedly for a "GSXR 600 750 K4 K5 2004 2005" and are similar to the Duc cartridges in general layout; specifically the top nut is the same style but has the M12 thread:



The other one is for a "GSXR 600 750 2006 2007" and is a bit different: The rod is M10 at the top and would fit the Duc top nut if the length was correct, and has a much simpler top nut:





The basic cartridges are otherwise similiar.

 

does anyone know if the 96 - 99 forks are any good?

 

My brother has a 98 750 gixxer, but he told me that closing the comp adjuster doesn't make the forks rigid on compression. I can probably inspect his forks next weekend to find out.

Torbjörn, do you know if the rebound adjuster needle for the k6 cartridge would fit into the ss fork cap? At least the k4-5 and 900 ss rebound screws are interchangeable in the fork caps.

Impulsive_duc: you can easily open and close one fork cap at a time without unloading the forks, but to measure oil level the forks need to be fully compressed. But if you know how much oil to subtract, then you could use that trick without a front stand. Just do one fork leg at the time.

 

Torbjörn, do you know if the rebound adjuster needle for the k6 cartridge would fit into the ss fork cap? At least the k4-5 and 900 ss rebound screws are interchangeable in the fork caps.

Sorry, but I don´t have much of a clue as to which K model GSXR is which. I tried the top part of the needle from the "...2006 2007..." cartridge shown previously. Though totally different in style (no clickers, for one thing), the thread is the same.

One other thing; I used to think that a fork that locked up on closed adjusters is a good fork, but I don´t think so any more. The important thing (in my humble view, that is ...) is that it reacts to adjuster settings. Assuming no "external bleeds", a fork that really locks up on closed adjusters is a fork with a pretty stiff shim setup. For comfort reasons, this might not be what you want.

 

Showa

Sorry for the slow reply, I did not know there were so many suspension engineers on this forum.

My recommendation would be 130, fully collapsed, spring out, per the SMC manual.

No Showas get stiff when the compression adjuster is fully seated, as the factory must account for the adjustment range that it does not become unsafe. You will find a couple major things (besides oil wieght) that affect this.

-Cartridge bushings, this is the upper bushing in the cartridge, if worn, the cartridge does not seal very well, and their is no control of the fluid
-Internal Damper Rod size, early (steel Cartridge) 8mm, Late (Aluminum Cartridge) 10mm damper rod. The larger rod displaces more fluid when entering the cartridge, so you have more fluid to work with.
-Valve stack stiffness, this is self explanatory
-Valve face, the portion that the shim rests against is critical. Some valves (reb and comp) have a small angle in the face, this is to preload the shims, this delays the opening of the shim. However, they are typically flat, especially in the standard pistons. On 600 grit and a flat plate, face them by hand, finish with 1000 grit. Press evenly, move in a circle, rotate the piston every 3 circles. This will ensure the piston face is flat so the shims seal properly
-Check valve (Comp and Reb) these must seal, if they (the shims) are not perfect, they will leak when they are supposed to seal.

So endeth the lesson....LOL

Thor

 

Thank you all for great advice.

Unfortunately on my SportClassic, "trick" did not work. Fork did not have enough preload to reach nut. Gap was too small to fit tube. See attached.

Even the 3.25mm OD tubing I had was too thick. It would not fit in gap between (preload spacer/lower) or (spring/lower). Syringe needle tip was metal (16 ga) and fit, but was only 2cm long.

So it is possible to do bradblack way, but you need a very fine, very long metal tube to connect to end of rubber tube/syringe. Finer than plastic tube at end of wd-40 can... (tried that too.)

Also, be careful. Probably should loosen top triple bolt if undoing/redoing cap nut. Otherwise compression makes it very difficult to turn, may damage cap.

Edit: McMaster-Carr supplies this precision miniature tubing (aka "hypodermic tubing") in 3ft lengths for around $15.

If you know the stanchion diameters, and use my calculation above, it should allow you to play with different oil levels completely externally.​