Well, vibration is relative. The Wilksch 3 cylinder is fine (see
www.wilksch.com). But the Renault 4 stroke (car motor put in a plane) was too troublesome. The Centurion is a Merc A series 4 stroke and is OK (just).
A two stroke is smoother, each burn is less explosive than in a 4 stroke ('cos you've only got part of the revolution to do it) but there are twice as many. It's smoother - it's good.
That's why I follow this path. But you're right, you gotta be on the watch.
Malc (What's the diesel related idea??????)