ZX600 shock oil change
So, you got yourself a ZX600 shock for your 250, and now you realize it's at least ten years old, and the chances of the oil in it ever having been changed are slim. Here's what to do.
Let all the air out of the shock before you start. The Schrader valve works just like a tire's. Note, however, that the oil and air in the shock aren't separated. If you hold it at this angle, some of the oil will come out with the air.
The shock depends on orientation (how it's mounted on the bike) and the force of gravity to create a situation where you can add and remove air without venting oil. So, if you press the Schrader valve in while holding the shock sideways or upside down, then the air pressure inside the shock will be able to force oil out of the shock.
Use a 10mm wrench and remove the entire hose from the shock body.
Drain the old coffee snot oil out. Heating the shock body first helps get it all. If you feel that you're not getting as much fluid out as you should, hang it upside down for an hour or two, along with first applying the heat. Remember that there is a rubber bladder inside, so don't go overboard on the heat. A hair dryer should do.
There should be about 8 oz of liquid in the shock body.
Oil used was PJ1 15wt fork oil (230 lb rider). Many Concours owners use fork oil as well (see below). 15wt is quite a bit too heavy. Even 10wt will negate most or all of the damping settings of the shock. Aftermarket shocks use 5wt - 7.5wt oils to keep the usable damping adjustments within the center third of the range. Unless you are really large, those should work for you, too.
If you are a more sportly rider, you should use a suspension fluid specifically designed for shocks, such as Bel-Ray HVI Racing Suspension Fluid or Maxima Racing Shock Fluid. This should provide better protection against viscosity breakdown.
To refill the shock, find a syringe of some type. This is an old syringe that was used to fill toner cartridges. Squirting the fresh oil in should be no problem.
Inspect, clean and regrease the o-ring on the hose end before screwing it back in.
Replace the hose, then install the shock.
Make sure to change the oil at least every five years.
With this new shock and new Race Tech springs, it now feels like a different bike. I took her out for a ride on some twisty bumpy backroads. UNBELIEVABLE!! The most noticeable change is how smooth and stable the bike remains in-between gears. No wallowing. Minimal fork dive. Holds lines better. Everything you've come to expect from these relatively simple suspension changes.
I kid you not...it really does feel like a different bike. Overall the bike actually sits a tad HIGHER while stopped. This is due to a combination of less sag at both ends.
Time to ride!