>>have you had the opportunity to examine a hard-run bearing shell from any donor-like Ducati's big-end bearing, or seen any calc's on relative dynamic forces per potential usage as a single?
I'm not sure why a big end bearing would know how many other cylinders there are. I could make a V8 with the same dimensions and each conrod would see the same loading as the twin, or single. I have run simulations to confirm there should be no problems with bearing loads.
>>AFAIR, this was one of the reasons Ducati went down the complex 'super-mono' faux-twin route
The Supermono was a student design project by Terblanche (who unfortunately peaked early) and was anything but complex. Not to kill a legend but the balance rod idea is nice but was making lemonade with lemons as he had to reuse existing parts and patterns. A 90 degree twin has zero primary vibes and the SM engine mimics the twin's primary balance characteristics. The secondary vibes of a twin and the SM are the same and each conrod big end (there are still 2 in the SM) add up using vector addition (45, 45, 90 triangle) so the magnitude is 1.414 (1, 1, Sqrt 2) the size of one cylinder’s secondary vibration and twins usually have short-ish rods so high secondary vibes. The Duc rod is a 1.85 ratio giving a combined secondary vibration magnitude of about 38%. For a single with a counterbalance shaft you also have zero primary vibes. For the secondaries I am using a long rod (~2.2 ratio) for lower secondary vibes and since there is only one cylinder it is 1 times those lower vibes, which comes out to a vibration magnitude of 22.7%. So overall a counterbalance shaft with a long rod in a single will have about half the vibration levels of a well-balanced twin or single/balance rod. And have a more compact engine design.
https://motochassis.com/Articles/Engine ... alance.pdf
>>BMW also did such a dynamic solution with their current 360 degree twin
The balance rod here is dynamically very different, it has its own throw which is less than the stroke. Leave it to the Germans to solve a problems uging twice the complexity as everyone else.
>>Likewise, one of the issues with Cosworth's DFV 1/4 cut for the Norton F750, back in the day, was the massive crankcases required to contain the recip-forces, counter-balancers or no
That was the Norton Challenge and the crank was not much different than their other parallel twins. There is one about 50ft from where I am sitting. Let the engine hover around 3krpm too long and the cam belt jumps a tooth. I think it had about 70lbs of internal rotating weight.