It's been suggested I write and sell a booklet...
Well I have and it's free! I'll cut and paste some of it here from
time to time.
view it at: http://hhscott.com/evinrude/omc_stringer.htm
Why are the 1962 - 1985 OMC Sterndrives called "Stringers?"
The term "stringer" refers to the unique mounting method for securing
the "inboard" engine and "outboard" stern drive internally to the
boat's hull using a stressed support frame much like the stringer
support found in boat hulls. The "stringer" mounting system allowed
retro-fitting the new stern drive power systems into existing boats
without the need for building up the transom to support the external
stern drive assembly (as did competitor's installations).
However, many boat builders considered the stringer's mounting
dimensions to be a drawback, when compared to competing MerCruiser or
Volvo sterndrives. The early (pre-'72) stringers were 4-inches deeper
and some 9-inches wider than their competitors, requiring boat
builders to make expensive design changes to accommodate the OMC
sterndrives. Another unique OMC stringer design element is the transom
aperture location. The large rubber boot is positioned approximately
1.5 inches "port" of the transom/hull centerline to accommodate the
TILT motor and hammer-blow clutch mechanism and quadrant gear.
Das Boot:
Two stringer mounting options were initially offered: a transom mount
and beginning in 1966 a floor mount. Both systems allow the entire
assembly to float within a rubber seal or boot, rather than rigidly
bolting the stern drive to the transom. This helps to reduce NVH
(Noise, Vibration, and Harshness) and insures unparalleled smoothness.
OMC's ball-gear upper drive interface also permits a full 90 degree
turning radius and 75 degree "Hi-Tilt" lift position (shown above).
Stringer-powered boats can turn in half the distance of other stern
drives and it's not unheard of to hear of owners changing props in the
water with the drive in the fully raised position.
Three stringer steering system options were offered to OEM boat
builders:
1) the rope/pulley/cable (used on ALL OMC-built boats),
2) the mechanical rack system with external tiller arm, and
3) True-Course worm gear and sector steering employing a
push-pull cable system.
All pre-1967 OMC boats use a very thin (1/8-inch thick) fiberglass
transom, and a steel "stringer" frame for transom integrity and the
upper rear engine-transom mounting. The early OMC sterndrive units
were all factory-pre-trimmed using metal shim plates under the front
and rear motor mounts. Floor mounting is preferable in higher power
installations as it eliminates transom stressing and can directly
transmit thrust forces to hull stringers. It also permits easier
adjustment thrust angle trim.
In 1972, OMC engineers introduced a novel power trim system,
SelecTrim, initially on four and six cylinder models, and later on
Ford V8 units. (The OMC stringer ball gear drive design doesn’t allow
the drive to be tilted/trimmed under power separately from the engine
without excessive wear on the ball gears.) The complete engine and
drive assembly must be pivoted within the boat to trim the drive and
propeller's angle of thrust. With SelecTrim, the front engine mountis
power-lifted or lowered to change the propeller's thrust angle of
attack. SelecTrim should not be confused with the separate, fast
acting electric lift-tilt, a standard item on all OMC stringer
sterndrives for trailering, shallow water operation or beaching.
SelecTrim was typically combined with the shorter leg outdrive.
OMC stern drives were usually painted white (late model Evinrude boats
used dark blue) and had a large circular rubber surround seal or boot
in the transom, although later (post-1968) a rectangular boot was
used. The single transom mounting ring or boot accommodates all
cooling, exhaust, control and steering elements, meaning no other
through-transom openings were required (very unusual for the early
sixties). Propellers were pin drive and the exhaust was not through
the hub, but exited behind the propeller via a port that doubled as a
cooling water inlet and adjustable rudder trim tab. The "Electric
Stringers" are infrequently referred to as the "Model 14-family" of
stern drives, probably named so for the introduction of their 14-inch
diameter props.
By following some simple precautions, "Electric Stringers" can provide
years of reliable service in the right hands. Don't be fooled into
thinking these drives are inherently unreliable.
OMC Electric-shift Stringer Precautions:
Always operate the electric hi-tilt/lift in the fully down position
when the engine is running or is started. It was not designed to be
used as a power "trim," for adjusting prop shaft thrust angle. The
unit can be operated briefly in a partially tilted position, as in
shallow water or beaching conditions. (It's important to protect the
upper unit ball gear drive)
Do not operate in reverse at more than 1000 rpm for a period longer
than 3 minutes. Overheating could occur, as the intake water pickup
efficiency is diminished.
Always use the correct OMC "C" or "premium blend" lower case
lubricant. Check upper and lower gearcase lubricant levels before each
use. Change lubricant seasonally. (Protect the electro-magnet coils &
springs).
Do not electrically engage forward or reverse gear switch for long
periods of time as electric shift coils draw a battery current of 2.25
amps (when switch is on) have no way of cooling out of the water. (You
also will over heat the ignition coil and ballast resistor when the
ignition key is left on for extended periods of time).
Always shift or engage gears at lowest possible engine idle speed,
ideally less than 650 RPM.( It's important to protect the lower unit
spring tabs). Well-tuned, smooth idling engines are essential to
smooth shifting.
Always closely monitor engine operating temperatures, for proper
impellor cooling water pump supply operation. Do not operate above
1200 RPM on garden-hose adaptor. (The "tattle-tale" ("pisser") stream
is your friend!)
Always refrain from changing the steering angle with stern drive
tilted in the "UP" position (especially when fitted with "rope/pulley"
cable steering).
Partially raise stern drive unit (in a centered-position) before and
while trailering and while launching (to protect the lower skeg from
dragging). Insure lowest part of drive unit is 15 inches above ground
when on trailer. Store drive in fully down position.
Do not confuse the first-generation, "Electric-shift Stringer" with
the second-generation OMC 400 and 600/800-series (also referred to as
ball-gear drive "Stringers") drives introduced in 1978, which used a
hydraulic assisted mechanical shift and thru-prop-hub exhaust. A third-
generation, U-joint-driven OMC stern drive was introduced in 1986 and
that drive is referred to as the "Cobra" series. A fourth-generation,
OMC/Volvo Cobra SX drive came out in 1994. A more complete OMC
sterndrive history can be viewed here.
Received on Sunday, 24 May 2009
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