Nice thread, and I've wondered the same thing.

As to thrust, the tranny is already set up for thrust (witness the amount of
polished shaft sticking out from the cutlass, at rest, the amount of thrust
forward taken up by the engine mounts and whatever else being that polished
amount - on ours, about 1/4")...

Auto trannies that I've had my hands on deal with the thrust by a splined
shaft at the tranny, with the limitation on thrust being controlled by the
rear suspension, and the up-down-left-right differences in length being
dealt with by the splined shaft. However, that shouldn't be needed by any
normal boat tranny.

Having the engine on normal mounts is, to my mind, an argument about not
being all that fussy about alignment (not that I am not), given the amount
of play in them, either under thrust, or from the vibration inherent in any
normal diesel. I can't imagine that more than .004 differences wouldn't
occur in our case, the level of aligment required.

L8R, y'all.

Skip

--

Morgan 461 #2
SV Flying Pig KI4MPC
See our galleries at www.justpickone.org/skip/gallery !
Follow us at http://groups.yahoo.com/group/TheFlyingPigLog
and/or http://groups.google.com/group/flyingpiglog

When a man comes to like a sea life, he is not fit to live on land.
- Dr. Samuel Johnson

On Tue, 11 Sep 2012 09:59:13 -0400, "Flying Pig"
wrote:


As to thrust, the tranny is already set up for thrust (witness the amount of
polished shaft sticking out from the cutlass, at rest, the amount of thrust
forward taken up by the engine mounts and whatever else being that polished
amount - on ours, about 1/4")...

Auto trannies that I've had my hands on deal with the thrust by a splined
shaft at the tranny,

===

Auto trannys don't have to deal with thrust, suspension components do
that.

Speaking of thrust however, this is a good time to check that your
shaft is firmly locked into the coupler with shaft indentations and
safety wire on the set screws. More than one boater has had the
experience of reverse thrust taking the shaft out of the boat. You'll
want plenty of reverse thrust to properly set that new anchor of
yours.

"Wayne.B" wrote in message
news

Speaking of thrust however, this is a good time to check that your
shaft is firmly locked into the coupler with shaft indentations and
safety wire on the set screws. More than one boater has had the
experience of reverse thrust taking the shaft out of the boat. You'll
want plenty of reverse thrust to properly set that new anchor of
yours.


Good thinking.

When we had the shaft shortened, we did it from the coupling end so as to
make it simplest (no taper, threads, etc.).

Previously, and, now, this time, once we'd gotten the
less-than-.001-undersized shaft in the coupling and keyed (new keyway, of
course, the bulk of the prior having been cut off), the hole in our coupling
which took the square-head bolt was used to center-dimple the shaft, then a
vee drilled out to accept the bullet-nose of that bolt (with the coupling
removed, of course).

When I put it in, I used Loctite Blue, and then safety wired it. The other
two security mechanisms are very stout, Loctite'd and lock washer'd hardened
7/16" bolts squeezing slots.

I think we're probably ok :{))

L8R

Skip

--

Morgan 461 #2
SV Flying Pig KI4MPC
See our galleries at www.justpickone.org/skip/gallery !
Follow us at http://groups.yahoo.com/group/TheFlyingPigLog
and/or http://groups.google.com/group/flyingpiglog

When a man comes to like a sea life, he is not fit to live on land.
- Dr. Samuel Johnson

On Tue, 11 Sep 2012 04:04:57 -0500, Richard Casady
wrote:

On Sun, 09 Sep 2012 05:09:49 -0500, Rick Morel
wrote:

On Sun, 09 Sep 2012 08:18:17 +0700, Bruce
wrote:

If you were to use two universal joints and a short intermediate
shaft, as you suggest, then you would require a thrust bearing
somewhere on the propeller half of the shaft installation. Not that
this hasn't been done, it has, and is done. BUT, it adds to the cost
and space required for the engine/shaft installation and isn't really
necessary in most smaller boat installations. The rigid shaft and
coupling has worked successfully for years and years.

Look up aqua-drive (I believe it is called).

Ah-ha, I didn't think of thrust! LOL! Shows what happens when one
doesn't think something all the way through.

I was basically struck by the idea that a single U-joint wouldn't
really be very different from no U-joint. It would correct for angular
error only. That's why auto driveshafts have two, to correct for
angular and positional changes as the much "looser" mounted engine and
sprung rear end dance about.

You're right, Bruce, the rigid shaft and coupling is very KISS and
effective, and has proven itself. I've never had a problem over a
period of many years and many miles.

We had a jet boat with a drive shaft with a U Joint. A turbocraft with
a 109 hp Graymarine engine.

And no propeller :-)