Installing an SV650 shock
There is such a thing as using the right tool for the job. For all but possibly 2% of Ninja 250 riders, this isn't it.
Disclaimer: At a spring rate of 510-550 in/lbs, this shock is grossly oversprung for anyone under about 275 lbs. It is not recommended for use on the EX250, except for a handful of people who might benefit from it. Average-sized riders almost always find it too stiff.
Disclaimer 2: Rich Desmond of Sonic Springs says: " I really don't recommend this swap, but if you're doing it you should know that the first and second generation SV shocks are different. The first gen (99-02) is longer and stiffer than the later ones. I'm assuming that the later one will work better."
Disclaimer 3: From Jeb, who wrote the original article: "This is a long and fairly arduous job, and the shock is not really well suited for the EX250. It's oversprung, too fat, and is really no better than the EX500 shock in the end; for a bigger person (250+ lbs), this shock would probably be as suitable as an EX500 shock, only much harder to install."
All right, enough warnings; here's the 10-step process, with a first-generation shock as the victim:
Before you begin, note that the SV650 shock is practically 1" longer than the EX250 shock; this will raise the rear end about 2.5" working through the swingarm linkage. This is way too high unless you're running a 120/80 rear tire and/or raising the front suspension. It would be best under most circumstances to drill a new hole at least 1/2" above the existing hole.
1. Drill out the shock's lower 10 mm hole to 12 mm, to match the EX250's lower rear swingarm linkage, or drill a new 12 mm hole higher on the shock. Drilling the new hole so that the SV650 shock is the same length as the stock one is the best way to go. If a 12 mm drill bit is not available, use a 31/64" bit, which is very close. A drill press is best for this, as the holes need to be carefully lined up on each side of the shock fork; also, there's a lot of steel to drill through.
2. Use a Dremel to deburr the edges of the hole just drilled.
3. The 650 shock's lower mount (clevis) is a little too narrow to accommodate the width of the EX250's lower swingarm linkage. For such mounting issues, grind before being tempted to bend. You can take some off the shock linkage, the clevis, or both. You won't have to grind much when you consider being able to take from 4 surfaces.
4-6. Now it becomes more difficult. The upper race from the EX250 shock must be pulled out and put into the SV650 shock, after the SV650 shock's race is also removed. The tolerances on these are very tight, and the only way to get this done without damaging the races is to use a gear puller. A 3/8" base, 11 mm socket on the end of the puller screw will put more pressure on the outside of the races, where it's needed. This will require careful placement of the puller claws and a significant amount of force to turn the screw enough to displace the races.
An alternative: A gear puller is not always the easiest way to accomplish this task. A trip to your local machine shop to have the races pressed out and then back in, along with the drilling of the lower mount hole, will cost you a few bucks, but should be much easier.
Once the races are removed from both shocks, call it a day and put the EX250 race into a freezer overnight. The next day, heat up the shank on the SV650 shock with a torch (not too much, as it's sitting on top of a valve containing compressed nitrogen), then use a hammer to start the race into it. Use the gear puller again to press the race into place; make sure it's centered. (This is the point where you should realize that a machine shop may be in your best interest).
7. Use a Dremel to grind away a bit of the top edges of the lower swingarm linkage; this will prevent the fork on the shock from rubbing the linkage body.
8. Grind away the top edges of the shock body below the shank. Again, don't go too far; just smooth out the sharp edge a bit.
9. Grind away the bottom edges of the upper shock mount behind the main swingarm pivot; this will allow the shank to reach the mounting hole without the shock body contacting the bike's frame.
10. Install the shock, torque each bolt to 33 ft/lbs, and check closely with a worklight to make sure there are no clearance problems.