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Discussion Starter #1
I modified a set of Monster S4 Showa forks to use the fork cartridge and valving from some Showa SBK forks (I was told they were from a 999 - they are 53/53 at the triples and have TiN sliders and have GD161 cast into the lower stanchion). In the original S4 fork the spring sits at the bottom of the fork tube around the cartridge with a spacer tube on top. In the SBK forks the spring is much shorter and there is a washer that sits on the top of the cartridge that the spring sits on and then there is a short spacer tube above. When I look at the parts book for the 999 forks, the spring looks like it should be at the bottom around the cartridge. Can anyone tell me what the correct configuration is?
 

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Discussion Starter #3
Does the spring sit down in the bottom around the cartridge or does it sit above the cartridge on a washer? The SBK fork I have looks different than this image. #7 is the entire compression valve with the adjuster and it is inserted through the lower fork stanchion and threads into the bottom of the damper tube. The damper tube does not have a ring at the bottom like is shown and the spring sits on a thick aluminum washer that is placed over the damper rod and sits on the top of the cartridge. Then there is a short preload spacer with a black plastic washer at the lower end that sits on the top of the spring and extends a little bit into the spring and into the spacer tube to hold it in position. At the top of the spacer tube is a white washer that extends a little bit into the preload tube and on top of that a small metal washer that the preload adjuster pushes on.
 

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Here is an exploded view of the donor 996 fork that I bought. You can see there was a spacer below the spring as well as above it (which was damaged).

985411
 

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Discussion Starter #6
Is the 996 and 999 fork similar inside? The 996 fork looks similar to how the S4 fork was configured except it has a short needle rebound circuit and there was no lower spacer.
 

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i'd say it really doesn't matter, as long as the cartridge tube can support the load and the spring is preloaded correctly.

but from memory - did this a couple of weeks ago - the 999 fork is like the other sbk forks in stacking, in that it has a steel tube maybe 100mm long under a washer under the spring, then the steel tube with plastic ends on top of the spring.

someone may have been in there before you too.
 

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Discussion Starter #8
On the SBK forks does the entire compression valve come out the bottom when you remove the adjuster bolt? Or does just the adjuster come out and the compression valve stays in the bottom of the cartridge tube?
 

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Is the 996 and 999 fork similar inside? The 996 fork looks similar to how the S4 fork was configured except it has a short needle rebound circuit and there was no lower spacer.
999 cartridge has the compression piston as part of the adjuster that goes in from the axle recess, and the cartridge tube screws onto that. in the 996 and most other (older) showa the compression piston slips into the bottom of the cartridge and is held in by a round circlip and a couple of dimple peens.

apart from that i think yes, the same. i have one here i can split if you really need a photo of it.
 

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Discussion Starter #10
When I get time I'll take some pictures of what I have and post them up for comment. I don't think it really matters either way how the spring is installed as long as nothing is rubbing and the fork is setup properly. What I did was have the lower stanchions from the S4 forks machined out to fit the compression adjuster from the 999 fork and I installed the 999 cartridge into the S4 fork tubes. I reassembled everything using the S4 spring and preload spacer and everything seems to fit ok but there was less preload on the spring because the 999 cartridge has more extension. I reinstalled the forks on my bike (a 2007 GT1000) and everything seems ok except I am getting a metallic clank from the forks on extension (like when dropping off the backside of a bump) and I was wondering if the spring is hitting the cartridge.
 

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the showa forks will often make a single sharp noise when they start to rebound. i walked around the workshop one day at my previous employer and pulled up on every sbk showa fork bike i could find to illustrate it to a customer. never found a cause of it, and once they're apart they don't seem to do it.
 

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Hello,
older SBK forks have steel cartridges and the compression adjuster nut from below in the stanchion, as in the picture above. 999 onwards has the complete stack / adjuster nut, that also holds the cartridge in place.
If you intend to take the compression piston off (to clean / change shims etc), be extremely careful when loosening the nut, as the alu tower is extremely brittle and breaks very easily.

While you have the forks apart, I´d trow away the hydraulic stop on the cartridge rod; it will give you a few mm of working travel.

It does not matter where the spring sits, I usually make a new bottom spacer from alu tubing if I need to adjust the total length of the package, and use the original top spacer tube.

Kind regards,
 

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Althought not directly linked to the original post, I'll post my question here since the title matches. I was under imperssion that 749S and the 749 base model (2004) have identical front forks but then I read from some old Ducati review they don't have. I would need some spare parts for my base model forks and I was planning to buy 749S fork for a donor.
 

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Hello,
older SBK forks have steel cartridges and the compression adjuster nut from below in the stanchion, as in the picture above. 999 onwards has the complete stack / adjuster nut, that also holds the cartridge in place.
If you intend to take the compression piston off (to clean / change shims etc), be extremely careful when loosening the nut, as the alu tower is extremely brittle and breaks very easily.

While you have the forks apart, I´d trow away the hydraulic stop on the cartridge rod; it will give you a few mm of working travel.

It does not matter where the spring sits, I usually make a new bottom spacer from alu tubing if I need to adjust the total length of the package, and use the original top spacer tube.

Kind regards,
torbjorn, do you put the aluminium tube in the bottom and a washer on top of it then the spring? what thickness aluminium tube?
 

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I don´t have any of it here, but if memory serves, it´s 38 mm outside Ø, 2 mm wall thickness. I´ll check next time I´m in the workshop and correct if necessary.

I crossdrill them at the bottom to make sue there´s no restriction to oil flow; don´t know if it really makes any difference, but id I do, it does not matter, so to speak.
I also crossdrill towards the top, so I can fish them out with a piece of welding rod or similiar, without draining the oil.

I put them in the bottom, use the stock support washer between the spring and the tube, and the stock pre-load tube on top.

I once tried smaller Ø tubing (approx 31 mm, with a 39 mm "foot" towards the spring. Not good, since it allowed the spring to wiggle around, rubbing against the cartridge.

2020-05-08 10.20.52 by torbjörn bergström, on Flickr
 

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Discussion Starter #17
Here Is a picture of what the original fork configuration was

985529


and her is how I configured it in the S4 fork

985530


I’m assuming from the comments here that the original configuration isn’t the standard configuration for a 999. Any ideas of what bike it might be from? I assembled the fork with spring and spacer from the S4 fork and since the 999 cartridge extends farther there is almost no preload on the spring. Should I cut a longer spacer so there is 10mm of preload on the spring in the assembled fork?
 

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Discussion Starter #18
Also, what is the correct torque value for the compression valve bolt? I found a service manual for the S4 forks that shows 30-40Nm but that is for the style where the adjuster bolt is bolted into the compression adjuster. It seems excessive for the 999 style where the compression valve is bolted into the cartridge tube.
 

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my 999 and 749 manuals also say 30 - 40, and they do show the correct internals. i think i used 35, didn't make a mess of it. i made a tool to lock into the top of the cartridge to hold it.
 

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Discussion Starter #20
Thanks for the info. I think I may have found the source of the noise. The SBK cartridge has about 25mm more extension than the S4 cartridge and when I assembled the fork using the spring and preload spacer from the S4 fork, there was still about 12mm of space above the preload washer and the fork cap when the fork was at full extension so when the fork would extend, the spring and preload tube could bounce inside the fork and I think that is what I was hearing. I bought some tubing today to make some longer preload spacers to match the SBK setup so hopefully that fixes the issue.
 
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