All the Showa forks for 50 mm / 54 mm triple clamps have the peculiar hydraulic layout that causes inferior function of the compression adjusters as described in Showa Blues part 1&2.
All, that is, except the forks of the 1000DS successor to the 900SSie from 2003 onwards. These forks have the normal hydraulic layout like any other cartridge fork, but all specimens I´ve worked with has a very soft valving set-up.
I had not had the opportunity to work on these forks before, but when a friend bought a 1000DS to use as a track day bike, he also wanted to upgrade the forks. Since I knew roughly what the forks looked like, I ordered what I expected to be the right kit from K-Tech, the 20SSK-INT-SHO3, which has a rebound piston holder with internal threads for the piston rod.
Fig. 1: 1000DS piston rod with stock and K-Tech rebound piston / shim assy.
Except, when we got the forks, it turned out that one leg was from a 1000DS, the other from a 900SSie. Externally the legs are almost, but not quite, identical:
Fig.2: 900 SSie and 1000DS upper fork legs.
Internally, they are different since the 900 leg has the inferior hydraulic layout. Since I wanted to make both legs the same, I would have to make a new piston rod for one of the fork legs whatever K-Tech kit I decided to install. Having bought the 20SSK-INT-SHO3 kit for the case, I decided to use that kit for both legs.
As it turned out, this was the wrong decision, since the 1000DS cartridge for some reason is shorter than in the M900 fork, for instance, and with the K-Tech kit installed the cartridge bottomed out at 115 mm travel. Not good, since the fork itself bottoms out at appr. 120 mm travel.
There are several different combinations of cartridge tube length, cartridge rod length, and then there are the shorter Monster / ST forks, and the longer SSie forks. I suppose there is some sort of system to it, even though I have not been able to discern it.
Fig.3: Various cartridges
It is possible to shorten various components in the Piston/shim kits enough to make up for the 5 mm of missing travel, but it´s easier to change to the 20SSK-INT-SHO13 kit instead, and make another new piston rod, this time with an internal thread for the rebound piston holder.
Once I got this far, the whole thing was pretty straightforward, but it had been one of the more labour intensive conversions I´ve done, due to the fact I was supposing things instead of checking first, and due to the fact two different fork legs were involved.
First some general notes:
Since this forum is a Monster forum, and these forks are only found on SS1000ie, strictly speaking this story does not belong here. However, since the family resemblance of these forks is so strong, I proceed here anyway.
Assuming you have a SS1000ie, and want to improve the forks action by installing a K-Tech kit (presumably, there are other kits around that will work just as well), what follows is one way to do so. Most of the general disassembly and assembly is the same as for the Showa forks described in Showa Blues, part 1&2. Therefore, refer to them for general information; in the following mainly the SS1000ie specifics will be described.
Compression valve conversion.
The Compression valve holder in the 1000DS fork is basically the same as in the “fake” Showas, but it is slighty upgraded design-wise: The valve holder is slightly longer, with a counter-sink in the hole for the hollow M6 screw; the screw itself is shouldered and is so supported by the holder before the threads begin. Good basic engineering, but hard to believe that the slightly simpler design in the “fake” Showas really save any money worth mentioning.
The conversion itself is pretty straightforward: With the valve holder in a 3-jaw chuck or similar, use a hot air gun on the stock assembly to loosen any Loctite, screw out the screw holding the piston/shim assy, and put the parts aside, making sure you keep track of the hollow screw.
After cleaning, put the kit piston / shim assy on the screw, making sure you put it on the right way. It is surprisingly easy to get it wrong, so take care: The shim stack is toward the valve holder. Put a small drop of Loctite on the threads, and torque down to some reasonable value. That’s all there is to the compression valve conversion, really.
Fig.4: M900 / ST4 / 900SSie and 1000DS compression valve assys
Rebound valve conversion.
This is slightly more complicated, depending on what you decide to do. Logically, one would like to exchange the rebound valve holder since you can then use the kit adjuster needle which has a much finer taper and thus, presumably, a finer adjustability. However, as described above, this leads to a problem with too-short cartridge stroke.
Fig.5 : Different K-tech rebound adjuster needles.
Fig.6: Showa stock reb needle compared to typical K-tech needle
The easy way out is to use the stock Showa rebound valve holder, and just substitute the stock piston / shim assy for the kit parts. Admittedly, I have never tested this, but see no reason it should not work well; possibly, the adjustment steps will be greater click for click due to the blunter needle, but general action should be much better than stock.
Fig.7 : Some different combinations of cartridge rods and rebound valve holder / shim kits. Stock Showa outside, K-Tech versions centre.
Before re-assembly, you should clean out the cartridge tube where you drilled out the dimples to get the valves out, or you will probably damage the piston O-rings when you push them into the tube.
When you´ve done this, and cleaned everything up, the re-assembly itself is pretty straightforward, and basically the same as for the other Showas; again, refer to Showa Blues Part 1&2 for guidance.
Fork spring conversion
The forks for the 1000DS track bike also came with different, and unknown, springs. Since we wanted to use linear springs, and wanted an assortment to choose from, we decided to use Öhlins R&T springs, since these are available in 0.5 N/mm steps from 7 N/mm to 11 N/mm. The same, or similar, is also available from K-Tech, and probably from others as well.
The Öhlins springs, at 240 mm, are much shorter than the stockers, so new pre-load tubes have to be manufactured. We used alu tubing in 28x31 mm dimension. This works well, but requires you take down the diameter on one side of the white plastic washer that sits under the top nut so it´ll fit into the tube.
Fig.8: Modding the pre-load washer to suit the new alu pre-load tube
I also made some connector pieces between the spring and pre-load tube to make sure the stay in place. These are made out of PEEK plastic we managed to find; that´s supposed to be a high-perf plastic much used in motorsport, but some other plastic will do as well.
Fig.9: Spring and pre-load tube assy
The total distance in the fork between bottom and top nut underside to be bridged by the spring / preload tube assy is approx 654 mm; I made the tube 10 mm longer to add some static preload, and since it is easier to remove metal, than to add it. We´ll see when the riding season starts if the static pre-load is correct or not. At least it is easy to correct.
I use 120 mm of air above the oil in all these Showas I do so people have a starting point; so far it seems to work well since no-one has asked me to change this. In my experience the shorter Monster / ST forks will need just under 1 litre of oil between them for the 120 mm air cushion; the slightly taller SSie / 1000DS will need annoyingly slightly more than 1 litre.
Disclaimer.
Although not difficult, these concersions affect safety-related components and should not be attempted unless you feel you have the correct tools and knowledge. Be thorough and careful, and you should not have any problems.
