Slotted Cam Sprockets

    

Part of my major ZRX rebuild is degreeing the ZX11 cams I had in the old 1100 motor. I have been lurking on the ZRX Owners Association message forum and have read what has been written about degreeing cams. The general consensus is that the stock 1100/1200 cams run well with Intake & Exhaust cams with lobe centers set to 103 degrees. This is retarded a couple of degrees from the stock position, which shifts the "power band" downward in the RPM range. I'm really interested in getting the bike to the dyno and doing some testing on some ideas I have about reducing overlap with the longer-duration ZX cams. The reason this is a big deal is that overlap is basically a leak, and motors with lots of overlap need more compression to compensate. Changing compression requires altering or replacing expensive bits, and that's not what I want to do.

Of course, in order to adjust the cam timing, one must have slotted cam sprockets. I have a small mill-drill and a modest collection of tooling, some of which is worthwhile, some of which is crap. Falling into the latter category are the cheap Chinese "Co-Ax Indicator". It's a shameless copy of a Blake Co-Ax, and it's a complete POS. That stands for "Piece Of Excrement". The POS would quit working whenever it was exposed to even the slightest bit of swarf. It's my bet that the tolerances are too large, allowing bits of swarf in where it promptly jammed the moving parts.

Without a co-ax indicator, you need to center the rotary table (rotab for short) by "touching off" the central hole and finding the center of each axis. I find that you need to do this three times -- once on the X axis, once on the Y axis and once again on the X axis -- if you do it perfectly each time. I also find that it helps to know the diameter of the hole -- you have a "check sum" to compare your touching-off numbers against. Since I'm pretty math-challenged, this is usually a 20-minute workout with the calculator. Then, to center the workpiece on the rotab, you need something that is centered over the rotab, so that usually winds up being the pin or cutter you used to touch off the rotab. I have had good success with a divider. Start the divider small, then open it slightly, adjusting the work each time until the divider touches equally on the left & right, and the front & back. Finely adjusting the divider is key. This is another 20-minute exercise.

All of this is avoided using the Blake Co-Ax. It's one of those "Genius" devices that you don't know how you lived with out. And, a bonus for me, it's simple to use. The above mentioned tedium is now reduced to about 3 minutes each, and Blake states that it has .002 accuracy when used with the short probe. Money well spent!

Since this is my business web site, I'll throw in a shameless commercial plug: cam sprocket slotting is a service I can do for you. Shoot me an email if you have sprockets that you'd like to have slotted. I can do this for any overhead-cam bolt-on sprocket. I'll do them for $25 each. New slotted sprockets are typically around $45 (and up) each, and then you have your old sprockets lying around.