3-53. PROPELLER SHAFTS - MAINTENANCE INSTRUCTIONS (Continued).
(3) Then the marine gear flange coupling is rotated 90, 180, and 270 degrees with
the feeler blade being moved around the flange again in each successive position.
If the alignment is correct, the feeler gauge will fit snugly, with the same tension,
all around the flange coupling.
(4) If the alignment varies during rotation, then further alignment is necessary, or
the marine gear and shaft couplings could be checked for improper face runout.
Face runout on the marine gear output flange can usually be corrected by
repositioning the coupling on its spline. Shaft coupling runout is usually due to an
inaccuracy of taper fit or key interference.
(5) Some boats are not structurally rigid and some carry their load in such a way
that they will "hog" or go out of normal shape with every loading and unloading.
Where this condition exists, it may be necessary to make a compromise between
the top and bottom coupling clearance by leaving a greater clearance at the
bottom of the marine gear output flange and propeller coupling. This clearance
might be 0.005 to 0.007 inch (0.013 to 0.018 cm) while the top would maintain the
standard 0.002 inch (0.005 cm).
(6) During the process of securing final alignment, it may be necessary to shift the
engine many times. When the final alignment is secured, the necessary steel or
hardwood shims are made up and the engine and gear is fastened in place. The
alignment is then rechecked, and if satisfactory, the coupling is bolted together.
(7) When a heavy boat is dry-docked, it naturally undergoes some bending.
Therefore, it is always good practice to unbolt the marine gear coupling and
prevent bending of the shaft.