Lotus Europa Community

Are you hoping to get all those used or would you like sources for those parts? Also do you have fabricating skills or access to such skills?

I checked the car of my brother (#460161) and to my surprise it had the same kind of reinforcement plate installed as #460234. The Europa S1 never fails to surprise me.
From the picture it is obvious that the plate acts as a reinforcement and not to cover an access hole. The body seam is also clearly visible. Could be that the plate has been fitted by the dealer or importer. My car #460230 has no traces of that plate.

Thanks much Brian and Gavin. Things are very much clearer. I see that my earlier thinking was not so much flawed, as it was the imagining of incorrect values to some of the force loads, and not giving enough credit to the lever action of the shape & orientation of the upright. This is an issue that has been gnawing at me for several years now. I'm going to sleep much better tonight. Cheers.

I do still wonder though if any of the driving forces might be sufficient to overcome the set up and momentarily apply tension force to the axle and thus stress the pins.

Unless you lift the wheel I don't think you will move the driveshaft into tension and even then, the load won't be a great deal.  But you've had an obvious failure on a pin and apart from not being fully shimmed in place I am struggling to work out a mechanism.

I'm not convinced it's a poor quality part, these things are in shear and I would guess that plain mild steel bar would do the job because the drive is supposed to be transmitted by splines, not the pin.

So I go back to shimming. Mine is so tight that I have to really drive the pins in and getting them out is equally tough. If yours drove out relatively easily then I'd add a bit more shimming.

The other, very blue sky thinking idea, was if it was possible to go from a very high compressive load to much lower stress and the cycling effect was enough to initiate a fatigue failure. That's very close to your proposal but I'm struggling with that one because you've always got some compressive stress. 

But if you are driving fast enough to lift wheels on our potholed roads, you deserve a medal alongside a free set of super high tensile steel pins !

Yep.
The fundamental forces in play in my super simple pic are gravity (red arrow) and the reaction from the spring (green arrow) – Isaac Newton's third law.
The core principal of the upright's function is that the spring acts on a lower pivot point and, thus, aways maintains a leverage advantage.

My slide-rule is in for service but someone smarter than me could calculate the leverage effect.
As a side note, the spring is laid over somewhat, so the actual spring force at the lower pivot will be something less.

So, if Colin walked into his engineers office with this upright, how would they stop it from rotating clockwise?
It's getting on for summer here, but to avoid a cold backside in the Northern hemisphere, I'd sacrifice a cornflakes packet to some cardboard aided design.