What is this washer?

[Marajin]

The direction of travel during engine operation would dictate that if the injector cam were to slip, it would tighten the screw for this plate and perhaps produce this problem. This is pure speculation of course.

Elabortating on only speculation, this would mean that if a particular shop has experienced repeating failures on this, there would be a high possibility that they could be causing or compounding the issue. Not cleaning the tapered mating surfaces properly with acetone, or perhaps lack of proper use of loc-tite 609?.

I have seen some repair shops go so far as trying to "rough up" the mating surfaces, only to accelerate these types of problems. "Roughing up" the tapered mating surfaces only reduces total contact area and creates a higher risk of slippage.

Cummins produced a bulletin for a very thin application layer of loc-tite 609 inside the taper of the gear. This is not so much to "glue" the components together, but the fact that as loc-tite 609 dries and hardens, it expands, increasing pressure and therefore friction between the components without having to over-torque retainer plate.