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MARINE TECHNICIAN TODAY | SUMMER 2013
belt tensioners and pulleys that various outboards have. Props should
be rebuilt or replaced if damaged to prevent harmful vibrations from
affecting the outboard. For safety, leave the propeller off until all the
servicing is completed. Check and replace the zinc anodes if needed.
Some 4-strokes use internal cylinder block anodes for cooling system
corrosion protection.
SPARKPLUGS and IGNITION
Remove the plugs and lay them out in order; note if any one
sparkplug looks significantly different from the others. A good plug
has sharp edges on the side and center electrodes with no rounded
or eroded areas. Flakes of carbon mean a possible rich running,
poor oil quality, leaking injectors, or open thermostats. A tan center
ceramic is ideal, but in outboards, the color can vary from off white
to almost black. Always check for the outboard manufacture’s latest
plug recommendations since changes may have taken place since a
manual was printed. Evinrude FICHT and E-TEC engines require an
additional step of positioning (indexing) the plug gap within 90° on
either side of the fuel injector nozzle centerline.
Ignition output is important for quick starting, smooth idling and
good acceleration. Perform the procedures outlined in the service
manual using the proper tools. If the spark is weak or not consistent,
find out why before going any further. Inspect the wiring, coils and
connections for carbon tracks or deterioration. Replace and gap the
sparkplugs if needed.
COMPRESSION
A compression test indicates the internal condition of the motor’s
pistons, cylinders and rings. Use a quality gauge and record the
readings. Most manuals do not list the compression pressures but
recommend results within 15% of each other on a healthy engine.
Some Yamaha and Johnson-Evinrude outboards have staggered
compression ratios so the bottom cylinders could have lower readings
than the upper ones, but they should be close from side to side. A
scored cylinder or piston may give a good reading at times because
of residual oil sealing the grooves. Occasionally a low cylinder will
improve after using a carbon-cleaning compound that frees up the
stuck piston rings. This is a good time to torque the head bolts while
the motor is cold if applicable.
Perform a leakdown test on 4-stroke engines as that is the only true
test of those motor’s internal health. By listening to air coming out of
the intake, exhaust, or crankcase it is easy to determine the source
of leakage on a cylinder and piston that does not hold at least 90% of
the air from the tester.
GEARCASE
Drain the lower unit oil. If clear water comes out or metal chips are
seen, the gearcase should be disassembled and inspected. Metal “fuzz”
on magnetic drain plugs is normal, but chunks or chips are not. Use
the manufacture’s recommended lubricant and refill from the lower
hole until oil appears at the upper threads. New gaskets or o-rings
under the screws assure a tight seal. Inspect the propshaft for wobble
and the seals for damage or fishing line. Grease the splines to prevent
corrosion and a stuck prop. Install a new cotter-pin if applicable.
LUBRICATION
Lubricate all the fittings with approved marine grease. Hood latches
and other sliding parts work easier with a slight film of lube. Use
silicone spray on carb linkages, contrary to the glob of grease that
some factories recommend. Avoid spraying around the starter drive
to prevent it from slipping. If you have a fuel injected Yamaha OX66,
keep silicone away from the oxygen sensor located on the starboard
side. Use care with a petroleum-based coatings if you spray it on the
engine for corrosion prevention. Sparkplug wires, rubber and plastic
could be affected. A greasy film will attract dirt and grit, plus it makes
future servicing a sticky messy ordeal. You will spend extra time
and shop rags cleaning off your hands and tools quite often to keep
fingerprints from the boat’s upholstery, trim, and gelcoat.
4-strokes require and oil and filter change which is best done while
the motor is warm. An experienced technician will soon learn a
servicing sequence that will maximize his efficiency in performing
the tune-up procedure in the shortest amount of time. For best
results use an FC-W certified 4-stroke outboard oil if you do not use
the manufacturer’s oil. That way it prevents any question of improper
lubricant use should a warranty situation arise down the road.
LINKAGE
Synchronization of the spark timing to the throttle opening and the
removal of the carb or throttle body linkage free-play are known as
“sync and link” adjustments. Service manuals show detailed step
by step instructions because of the importance of these settings
for a smooth running motor. Do not overlook the oil pump linkage
adjustments on certain 2-stroke engines.
Electronic fuel injected motors may require a throttle position sensor
(TPS) adjustment using a digital voltmeter. Again, follow the manual
exactly for this critical setting.
WARNING SYSTEMS
Test the integrity of the alarm systems. With the key on and motor off,
disconnect the temp sender wire connector and ground it with a test
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TODAY’S TECHNICIAN
