22 December 2006
What's an OMC Electric-shift "Stringer?"
"No other sterndrive tilts higher,
runs quieter, turns tighter, steers smoother, or shifts easier
than a well-running OMC electric-stringer..." -
OMC studied the
drive market (which included 16 other manufacturers) before
debuting in 1962, with the lightweight, oil-injected Model "480,"
initially rated at 80-hp, (eventually developing 88 and 90-hp).The 480 was developed to power the innovative OMC 17 Deluxe
original power-head was the 89.5 cu. in. displacement, 2-stroke V-4, derived from
the 1960-61, 75 hp Evinrude/Johnson outboard.
First-generation OMC "Electric Stringer"
stern drives shared either the push-button (Evinrude) or
single-lever (Johnson/OMC) remote control to shift the electro-magnetic, spring-shifted,
bullet-shaped lower units, first introduced on highline 40 & 75 hp OMC
outboards for 1962.
Johnson/OMC Single-Lever Remote
Evinrude "Selectric" Push-Button Remote Control
An innovative fuel injection system was
planned for the 480, but did not see production. However, the oil injection system did
do away with the need to premix
2-stroke oil and fuel.
From the beginning, all OMC
sterndrive units had ball-gear drive and "floating"
live-rubber mounting for smooth, quiet operation. Standard
equipment on all models included: electric power lift/tilt, remote
control electric shift, with choice of push-button or
single-lever control, and a choice of several propellers in
The electric shift used ingenious, electromagnetic
coils to engage either forward or reverse clutch springs. In
neutral, the clutches rotate freely around the clutch-hub. When
the operator engages a gear, the electric coil magnetically
causes the spring to grip the clutch hub. The harder it is
driven by the motor, the tighter it grips the hub, while the
other clutch spring remains in the relaxed (un-engaged)
position. There are no moving electrical parts to cause failure.
There are two circuit wires sharing a common ground between the
gearcase the the remote control helm.
The original "bullet-shaped" units require 17.5 oz of OMC
Type "C" lubricant in the lower gearcase. The
"bullet-shaped" lower units were offered on 1962 -
1968 OMC/Evinrude/Johnson 14-ft and 16-ft boats with the "DU"
"Bullet drives" would also see OEM-duty behind
II 153 (110 - 120 hp) fours (CU). The OMC V-4 (DU) was last
offered in 1968 and was replaced starting in1968 with the Ford
(UK) cross flow "Kent" OHV fours of 80 and 90 hp (NU)
||Early 480 Prototype:
Powerhead = 155 lbs
Intermediate = 62 lbs.
Outdrive = 80 lbs.
Total= 297 lbs
pre-production 480 prototype (above). Note lack of top cap and
curved exhaust housing. Anti-cavitation plates were extended forward of gear case
on production units (below).
||Final Production 480
In 1964, OMC introduced a more robust (higher thrust rating)
heavy-duty, electric-shift lower
unit and introduced three GM-sourced engines: 1) 120-hp Chevy
inline (153) four, 2) 150-hp Buick (225) V6, and 3) the 200-hp
Buick (300) V8 (later in 1966). OMC engineers evaluated and rejected the
Chrysler Marine 225 "Slant Six," which used a novel,
low-profile "pancake" horizontal mounting. Instead they
pioneered the marine use of the space-efficient V6, an engine configuration that
remains popular with boaters some 40 years later.
would replace the Buick V8 with the small block Chevy V8 in
1969, followed by the Buick/Jeep V6 being replaced by the Chevy
inline 6 in 1973. In the 1975 the 302 and 351 Ford
V8's were added in 175, 190 and 235 hp offerings.
higher-thrust sterndrive units
require either 33.9 oz (1969 - 1977) or 37.2 oz (1964 - 68)
of OMC Type "C" lubricant in the lower gearcase.
They are easily identified by their more robust and gently
"rounded" gearcase, as shown below.
The first-generation, electric-shift OMC drives remained in
production through 1977 with various engines from GM and
Ford. (View model number
listing.) Many evolutionary design improvements were made during the 15-year production span.
For 1978, a second-generation, ball-gear OMC Stringer (400/600/800-series)
design with a redesigned (V4 - V6 outboard inspired, thru-hub
exhaust) lower unit, which remained in production until 1985-86 and shared many
upper gearcase design
features of the original "Electric-shift" stringer.
It is important to always specify your
sterndrive's model number when locating parts.
OMC engineers deployed an unusual "ball-gear" drive
design totally unlike the "universal-joint" drive designs
employed by Volvo and MerCrusier, ironically the OMC design drew
inspiration from a 1931 Johnson stern-drive.
OMC Electric Stringer in 75 degree (25
percent more than competitive models) "Hi-Tilt/Lift" position
(electric motor-driven, lock-to-lock
in under 4 seconds)
Unit can be parked or held at any angle for mooring,
trailering or lower unit maintenance. Unique clutch pack/worm
and quadrant gear design permits shock absorbing action
to minimize impacts of under water obstructions, while
permitting efficient reversing. Shown above, is the 1966
HUE-14E, high-thrust gearcase, powered by the Buick
Read the interesting history of The
Great Stern Drive Conspiracy: How the Stern Drive was Invented.
Why are the 1962 - 1985 OMC Sterndrives
"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 MerCruiser or Volvo. 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 electric stringer design element is the transom aperture
location. The large rubber boot is positioned approximately 1.5
inches "port" of the transom/hull centerline.
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 OMC boats),
2) the mechanical rack system with external tiller arm,
worm gear and sector steering employing a push-pull cable
All pre-1967 Sportsman's use a
(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,
initially on four and six cylinder models, and later on 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 mount is 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.
OMC stern drives were usually painted white 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
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
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
(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.
- Always refrain from changing steering angle with stern
drive tilted in the "UP" position (especially when
fitted with "rope/pulley" cable steering).
- Partially raise stern drive unit 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
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.
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.
OMC offered two different
height profiles on these electric stern drives. A high-profile
upper case exhaust cover measures 15.5"A low-profile exhaust cover is 11". Pre-1967 units use a
four-bolt top cover, later units use five-bolt covers. Various
combinations of gear ratios and props
This table shows the various weights of the 1966 Evinrude
models (data from factory brochures). My 1971 OMC 307 Chevy
V8 modified Sportsman is also shown. Note how close an
outboard-powered (1966 100 hp Evinrude or Johnson V-4)) Sport-16
is to the V8-powered, 19-ft Rogue in power-to-weight ratio.
||Weight vs. Power
|I/O Total Power Package
||Outboard V4 - 100 hp
(w/battery, fuel tank & controls)
|n/a - (outboard)
||n/a - (outboard)
||90 hp V4 I/O
||120 hp I4 I/O
*HD lower unit
*HD lower unit
||150 hp V6 I/O
|215 hp V8 I/O
(* 2005 lbs
w/additional transom bracing)
||Rogue (Buick V8)
||200 hp V8 I/0
(Weights from published