In article , Roger Long
wrote:

Just skimmed it.

I think he's right but he's talking about something different than the
couplings faces being true and square to the shaft. If you have a
true running shaft pulled out of line by the engine moving on the
mounts or not being perfectly aimed towards the strut, that's one
thing and probably not a big issues as he says. If the engine is
trying to wave the far end of the shaft in a circle under the same
circumstances, I think you are going to have some noise.

I'd agree with you. What I don't understand, though, is why, *ever*,
you wouldn't have flange faces that weren't at right angles to the
shaft(s) to within extremely close tolerances. But then I'm a
fitter/machinist amongst other things and have a couple of lathes about
the place. Facing a flange off square is a 30 second job. Boring it to
a close sliding fit on a shaft, not much longer.

The whole issue of small boat drive trains strikes me as something that
shoulda been left in the ark. If I ever get my shed finished so I can
move onto the boat, I'm planning on mounting my engine/trans with a CV
joint between it and the shaft. This will require a thrust bearing on
the end of the shaft, but so what. I can mount the engine pretty much
wherever I want, on soft vibration reducing mounts, and forget about
drive train misalignment. We're only talking 30 HP or so. My tractor
PTO handles way more than that reliably. No thrust loads there of
course, hence the need for a thrust bearing on the shaft.

I can't understand why drive systems are hard coupled other than it's
cheap to do the first time and any subsequent maint probs aren't coming
home to the builder.

PDW