Parts that wear - spotting index arm

Spotting index arm

Spotting index unit location on top of back door
magic ring

The spotting ratchet can take a bite ....
spotting index arm

Spotting index arm? what's that? OK, so you haven't memorized the definitions in the glossary. If you want to peek now, the spotting index unit is defined.

The deal is that the arm on this unit is made from a metal that is softer than the ratchet (gear) that the arm engages, so over time the ratchet teeth dig a notch in the arm.

The effects of the operator solution
spotting index arm

The classic operator fix was to loosen the unit and offset it slightly, giving the ratchet teeth a new hunk of metal to bite into. Here we see that solution, but the unit wasn't shifted enough, so the teeth eventually worked back toward the original slot. The metal is already weakened, so the wear is accelerated.

Dennis A. also noticed that the plunger rest (right-angle hunk of metal that the plunger falls onto) was cracked/broken off. It looks like that's a weak spot, and over time the metal breaks at the right angle. This allows the plunger to fall lower down, which in turn allows the arm to continue to move against the ratchet.

In one sense, this is a good thing, because the arm is free to travel as far as it needs to engage the ratchet. On the other hand, this also allows the notch to keep getting deeper.

Brazing/welding the plunger rest will fix it, or you can epoxy another hunk of metal around the bend to reinforce it.

This is one of those things you attack with some imagination. Since a new replacement arm is not likely to be found, you wind up fixing the thing yourself.

Possible solutions

fill in the notch with epoxy/liquid metal (this probably won't work for long).
fill in the notch with real metal (weld). This is the best solution.
epoxy thin metal plates to the top and bottom of the arm, and fill in the middle with more epoxy
file the notch out and let the ratchet start again.
cut off the horizontal section piece of the arm and weld/epoxy on a new piece of metal
swipe another arm off a parts machine
do the operator fix, bending the arm and/or repositioning the unit to attack a good section of metal on the arm. This is probably the easiest thing, and will likely work fine until you start running out of unchomped metal - which may not happen on a home-use machine.

I've seen all of the above. After messing with this unit, you will need to adjust it. All that matters is the wipers on the spotting disk should be centered on the rivet heads when the ratchet is engaged on the arm. You can loosen the unit and slide it up/down to make the adjustment.