Stern Drives
The inspection of a stern drive unit can be
very difficult, or impossible it the
vessel is in the water. If the vessel is
not hauled for a complete bottom inspection
which would include the stern drive,
a lot would be left to chance. Often, during
the sea trial the stern drive can
perform very well and still be on its last leg.
A stern drive can perform
reasonably well right up to the point where it is about
to fall apart. Number
one, the outside casing is made from aluminum and the
inside parts, gears,
shafts etc. are made from various other non corrosive metals.
Electrolysis plays
a very important role in the condition of a stern drive. A stern
drive can look
very good from the outside, but the inside may be an entirely different
story.
Usually the condition of the outside casing can give you a pretty good idea
of
the condition of the inside. Most stern drives that have been poorly maintained
will show excessive corrosion. The casing literally turns to dust over time.
Typically a drive will be equipped with an array of zinc anodes which should be
monitored frequently during the season, as they tend to disintegrate at various
rates.
There are also several grounding wires within
or attached to the drive that must be
routinely checked. If the ground wires
fail, electrolytic action is enhanced.
I had the good fortune to inspect a vessel
with twin stern drives a while back.
One drive looked fairly new and the other
was badly corroded. The owner said
that he recently had the nice looking one
rebuilt and a new casing installed. I noticed
that he surface was not quite as
smooth as it should have been if it was, in fact,
a new casing, so I scraped a
little paint off in a couple of the rough areas. Not to my s
urprise, I
discovered areas of epoxy filler. Upon closer inspection I found that the
entire
lower unit had been re-finished, filled with epoxy and sanded reasonably
smooth,
and painted. The lower unit had not been rebuilt mechanically, only
c
osmetically. It turns out that the owner did the job himself to hide the
massive
corrosion problem and was about to do the second drive when his time
came for
spring launch. This is another example of the seller of a vessel
misleading the buyer.
