Jere Lull wrote:
In article ,
Peter Hendra wrote:


I have an engine alignment problem in that when my engine was taken
out of the boat in Port Sudan in the Red Sea, the mechanics who were
not marine engineers did not align it properly when they reinstalled
it. At lower revs it vibrates somewhat.

It has four flexi-mounts that are bolted to two longtitudinal engine
bearers and each is connected to the engine by a vertical threaded
bolt.

I would be very grateful if someone in the group could advise me the
sequence or process of aligning it again. The yacht is now out of the
water. The engine is a 37HP Nanni diesel with a "V" drive with a
plastic flexicoupling between the gearbox plate and the propellor
shaft plate.


You'll have to wait until the boat's back in the water, the rig is
properly tensioned and things have settled for awhile.

Then it's an iterative process of getting the height and angle closer
and closer, eventually winding up with the shaft in the center of the
shaft log and the drive plate exactly parallel on each axis. Then lock
the mounts down. recheck and bolt the shaft together.

Take the plastic piece out as you measure of course. It'll smooth things
if you're a bit off, but you don't want to have it always flexing.


You must align the engine and prop shaft by adjusting the mounts as
above so that the engine and prop shaft are pointing in the same
direction, at the same height and lateral alignment. Additionally,
you need to ensure that the prop shaft is aligned before you align
the engine to it. First, make certain you do not have a bent shaft
or warped prop.

Most prop shafts can be wiggled around somewhat and you need to
ensure that it is true and centered first. Keep in mind that on
many boats the prop shaft and engine is set off to one side by
possibly 1/8 of an inch to compensate for prop walk while proceeding
straight ahead. All inboard propellors will vibrate at some speed,
because of interference between the hull, the flow of water and the
prop.

After it is all set up, next time you yank the engine, consider
unbolting the engine mounts themselves from the engine bed and
pulling the whole works without disturbing the adjustment of the
mounts, still attached to the engine. Worked for me because the
mounts come out and can then be detached from the engine and
reattached with little or no movement using the original holes, etc.

Loose mounting holes, worn from repeated re-installation, are caused
by improperly re-inserting threaded fasteners into holes without
regard for cross threading. A screw should be turned backwards
until the threads are percieved to 'click' into the established
threads. Few workmen bother with this, and holes become sloppy,
requiring filling and re-tapping. Some loose holes may be snugged up
with heli-coils, or by coating the screw with wax and then filling
the hole somewhat with epoxy, and then re-inserting. Improperly
done, this can be a disasater if they need removing in the future.

To assist, you must find or make some reference marks on the boat
and then align the prop shaft and engine to the same spatial
relationship, using the reference marks on the boat and measurements
of the prop shaft and of the transmission shaft, using feeler gauges
between the drive flanges. These are precise measurements to be
sure, and while non too easy, are certainly not impossible.

The alternative is to make adjustments underway, "tuning" the
alignment for minimum vibration. Working around rotating machinery
is very hazardous. You would make the adjustments at the worst
vibrating rpms, taking note of eccentricities, possibly using a
strobe light keyed to the ignition or some mark on the flywheel, or
using a runout gague. Do not do this!

A friend of mine would use the approach of loosening all the
setscrew and then running the ******* hard and fiddling with it
until it settled in or broke, then resetting the screws. I do not
reccommend this, as in about half of the cases it would promptly fly
into pieces. In the other half , it would take longer to fall apart.
Sooner or later, he will lose an arm.

My father in law, God rest his soul, a Canadian veteran of Holland,
an old time horseman, woodsman and a farmer, would buy a bushel of
parts, bolt them together loosely with locking wire, let it shake,
and replace pieces whenever they broke. Many of our farms are run
this way and while farmers survive somehow, there are many
casualties. He is also reputed to have welded a steering knuckle on
his tractor, using the starting battery, a jumper cable and a coat
hangar. It got him home. He was scary in other ways, too.

Good luck.

Terry K