Can you post pics?
I have a 2000 SX and the plunger (black thing in spring in rudder casting) keeps peeking OUT of it's hole and gets bent. It appears the cam is rotating to far and allowing it to come out part way. JAMS and will not lock without dismantling it.
I'm not really understanding what you're trying to describe here. The plunger is supposed to come out of its "hole" in the casting. The plunger loads in from the top of the casting and pokes out so that it engages the recesses in the cam.
The black plunger has done this a few times and finally broke. I didn't have a spare so I tried a H16 WHITE round plunger that fit and seemed like it should work, but really doesn't seem to work well either. I also changed the cam. (To try and stop it from over rotating back which allows the plunger to come up and almost out of it's hole.
I wouldn't use H16 parts on the H18 rudder system. The plunger and cam are different (note that the cams look the same but have different P/Ns in the catalog, so I can only assume there is some subtle difference between them). If the cam is over-rotating, it sounds like you are not tightening the plunger screw enough.
I moved the adjustable shim inside the casting all the way forward to lock in the cam. It WASNT enough to allow the cam to pull up when I pull up on the cross bar, so I even drilled (reamed) the slot more forward to get an extra 3/16th more forward motion. STILL doesn't allow the cam to come up unless the tension screw at the bottom of the spring/casting is so loose it's about to fall out. And the water pressure alone would kick up the rudder.
This sounds like perhaps your rudders aren't drilled properly.
Any idea why these don't seem to be working? I do have a good bit of slop in the rudder in the casting... and a good bit of slop at the top arm mounts to the casting. Could this be part of it? It's REALLY annoying to not be able to lock the rudders down.
The system does not tolerate slop. Yes, you need to figure out the source of the slop and eliminate it. Slop usually comes from either poorly a poorly adjusted slider plate (cam plate), or mis-drilled holes in the rudder.
IS THE BLACK PLUNGER NEWER OR OLDER than the white one? Or is the black one 18 specific? The white one for the 16?
The 16/14 uses as round plunger, the 17/18/20 uses a rectangular plunger (side profile).
Try to get some pictures posted.