If you are going to tackle this job yourself, you should pick up a
dial indicator gauge and an articulated, adjustable post to use with
it. A magnetic base is convenient for working around engines.

Your engine coupling should have been machined true when the engine
was put together but needs to be checked.

1) Clean up the edges and faces of both coupling halves. Remove all
paint and rust, and get them as smooth as you can.

2) Set up the dial indicator on the edge of the coupling and rotate
the output shaft. There should be only a few thousandths change in
dial reading as the shaft is rotated. If the coupling has a pilot and
you can get the dial indicator to read on the edge, check that as
well. It will be a better reference than outside of the flange but is
tricky to keep the dial indicator on.

3) Set up the indicator on the face of the coupling and rotate. There
should only be a few thousandths change here.

If anything is seriously out of whack here, you should send the engine
and both coupling halves out to be reworked.

4) Calculate the weight of the shaft from the first bearing or
support. Multiply cross sectional area x length x .284 pounds per
cubic inch. Divide by 2. Calculate the weight of the coupling half
the same way and add.

5) Put a wire sling around the shaft as close to the coupling as
possible. Lift with a scale in the line until the reading is as found
in 4). Tie off shaft so scale retains that reading.

6) Put the indicator on the coupling edge, pilot (if any), and face
and check as you did with the engine half. If anything is out of
whack here, you should send the coupling out to be reworked.

7) Be sure the shaft is in the proper fore and aft position. Shim
and adjust the engine until a feeler gauge (spark plug gap gauge works
well) reads the same distance between the coupling faces all the way
around.

8) Put a straight edge across the coupling faces at the 12:00, 2:00,
4:00 etc. clock positions to be sure the centers of the two shafts are
the same. If the edges of the shafts are different sizes, you may
have to use a feeler gauge between a straight edge on the larger one
and the smaller.

9) Bolt and secure the engine mounting bolts.

10) Break for the day. If it's early, take a hike or go swimming.

11) Next day. Recheck all measurements.

12) Bolt up coupling.

This must all be done in the water. On a sailboat, the rig should be
tensioned.

If there is a long distance between the stuffing box and the first
bearing. You should unpack the stuffing box on land, calculate the
shaft weight ignoring the stuffing box as a support point, and hang
the shaft as described in 4) and 5). Then repack the stuffing box.
When the boat is in the water. Recalculate and hang using the
stuffing box as the first support point for the calculation.

Even if you have a flexible coupling, you should get the shaft aligned
as closely as possible. The exception is CV joints which need to have
an intentional angular offset of several degrees for best life.

--

Roger Long



"Peter Hendra" wrote in message
...
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.

Thanks
Peter Hendra
N.Z. yacht Herodotus