This is what happens
when you allow water to remain in the engine.
And the customer said "What are you talking about, there's
no rust in my engine."
only is there rust there is corrosion on the aluminum. Remember
there are three different metals inside. Aluminum, steel and
brass. It not the quality of the materials, it's the electrolysis
action between dissimilar metals.
basically have a battery when you have dissimilar metals together
and when you add salt water like this customer you really have
to maintain your engine.
you need run the engine dry (out of fuel, refer to fuel
and rust). Next dry off your engine competely. Compressed
air works great but a good bath in WD40 will do also. Squirt
in the oiling holes located just below the flywheel and on
the powee take off plate shown in the next photo. Earlier
outboards did not have these holes.
you flip you boat or cause the engine to become submurged in
salt water, you should disassembl the lower unit haves and the
covers on the engine crankcase.
need to remove your exhaust system also.
care and maintenace will help avoid rust and corrosion like
shown in these pictures.