So, I have an Aurora (Indian) Mills 1.3 MKII replica I finally got around to running. Far as I know, it was never run before, so I did some lighter running in on it (rich, low compression), and then started leaning it out and increasing compression a bit and backing it off, and repeating that cycle a few times per tank. I've allowed the engine to cool between tanks, and now have about 15 tanks through it (about 24 minutes of run time or so).
Using a Zinger 10x4, I've gotten up to 6600RPM, and up to about 7700RPM with a Master Air Screw 9x4. These seem to be decent numbers for these props, from what I can find, yes?
I noticed, however, that vibration was excessive at the higher RPM numbers, particularly with the 9x4. Now, I'm no expert on prop balancing, but I got both props to balance fairly well on a Du-Bro balancer. I'm sure I could fine tune them further, but they seem adequately balanced, and the PAW 1.49 I had the 9x4 on previously didn't seem nearly so "vibe-y" while running it.
My question is this: are long-stroke diesels prone to more vibration than a short-stroke diesel like a PAW? Or am I actually that far off my prop balancing skills and need to brush up? Or perhaps it could be something else wrong with the engine itself? I'll have to open it up and see if the conrod ends are worn, but they looked fine upon initial inspection, and I have a hard time believing just a few tanks could open the ends up that much so soon.