GaryDoug

I recently received two OEM Opti's for 93/94 from Tony at FBN for analysis and repair (if possible). I needed to disassemble them in order to access the plastic plate/carrier with the electronics encased. In order to remove it, I needed to remove the optical sensing disc from it's drive hub. Lo and behold, I find that it is spot/pressure welded to the hub in one small place. I could figure no other way to proceed except to use a tiny grinding bit to remove the disc material at the weld. Now I have the following problem. When the disc is attached back to the hub, there is play in the two elongated holes in the disc that align with the two pins in the hub, so that the disc can rotate about 15 degrees total, until the disc is held down by the rotor and backing plate. Even then it might eventually slip out of place from the vibration of the engine. I can figure no other way to fix it in position on the hub except to drill a small hole through the disc (.005" thick stainless) and the hub in order to install a small locating pin (press fitted). Naturally I would like to find a cleaner method since I am sure the disc will be very difficult to drill without damage. Any ideas?

Injuneer

Interesting.

The weld on my 94 was in a different location, maybe about 0.045" from the right hand "slot" in your photo. I ground it down to remove the disc, just to disassemble all the parts. If I reposition the hole I ground in the disc over the dimple the grinder made in the hub, the pins for the slotted holed are right in the middle of the slots. That would allow you to locate the disc accurately. On mine, with the weld having being closer to the hole, I think positioning it accurately, and applying a tiny dab of epoxy in the hole where the weld was might be enough to help stabilize it and prevent it from moving when tightly clamped by the rotor.

With the location of my weld, the "dab" would not be restrained by the rotor, so a small bump of epoxy wouldn't be a problem. But with yours being closer to the rotor screw hole, clamping the disc with the rotor would also apply the pressure of the back of the rotor to the "dab" of epoxy. Maybe fix the disc to the hub with a dab of epoxy, then sand the epoxy flush with the disc and put the rotor on nice and tight. Or, put a very small relief in the back of the rotor to just fit over the bump of the epoxy dab.

Another alternative would be epoxy in the slotted holes.

GaryDoug

Epoxy was my first thought. I don't have a problem with initially positioning the disc, but I guess my concern is that anything made of plastic (like epoxy) could crumble away in time. Then when someone replaced the rotor, there would be nothing fixing the disc in place. It wouldn't even be noticed since the disc is hardly visible when just installing the rotor, so nobody would see that it was up to 7 degrees out of time unless they lifted out the metal spacer and looked specifically at the pin location in the slot.
I am more inclined to go with a pin that would not decay and would allow the disc to be removed for service later... Hafta think about this some more...

GaryDoug

And by the way, I think I know why this one failed and if so, it's bad workmanship all over this "Made in Japan" item. Stay tuned..