I'll try for an answer: the pistons are moving fastest not when the
crank is at ninety degrees to the vertical but with the crank a little
closer to cylinder - so the crank and con rod are at 90 degrees to
each other.
This has the effect of introducing a vibration at twice crank rotation
rate.

Brian Whatcott Altus OK

On Wed, 16 Jul 2003 23:51:01 GMT, "Ken Coit"
wrote:
//
I'm not sure I understand why having pistons at opposite ends of their
throws simultaneously would increase the vibration, but then, dynamics was
never one of my favorite courses. If you have a quick explanation, I am all
ears.

Thanks for your reply, the quest is interesting to say the least.

Keep on sailing,

Ken
S/V Parfait
Raleigh, NC