bod43 wrote:

You might like this.
http://ibis.experimentals.de/downloa...lvibration.pdf

That URL would do well to be presented to any engine developer.
Moreover, it's not only engines with jack shafts or quill shafts
that are affected. I read a comparable piece that was - perhaps
still is - available on the net about the historical development
of some Pratt & Whitney engines.
The P&W work also mentioned pendulum crankshaft dampers, one
of the methods not mentioned in bod43's reference.

The automobile clutch friction plate torsion springs mentioned
in the URL aboveremind me of a feature of the first motorbike
I owned; a 1936 BSA 250 CC side valve model with girder forks
and unsprung rear end.
The drive side of the crank was splined. Over the splines,
a chainwheel was free to rotate, but outboard of its hub
was a wavy edged cylinder. On this a splined drive hub with a
complementary wavy cylinder was fitted, and a stiff spring
pressed the driven hub to the chain wheel via those wavy edges.
If the crank wished to move, while the chainwheel stayed fixed,
the driven hub would slide outwards against spring force.
This provided a soft drive characteristic always useful in a
single cylinder engine.

Brian W