Date: Sun, 24 May 2009 21:12:53 -0500
Lee,
Haven't looked at your sight in a while, very impressed.
Glenn
----- Original Message -----
From: Lee Shuster (lib1)
To: Evinrude & Johnson Boats of the 1960's and 70's
Sent: Sunday, May 24, 2009 2:00 PM
Subject: [OMC-Boats] So now that you have an OMC Electric Stringer......
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:
1.. 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)
2.. 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.
3.. 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).
4.. 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).
5.. 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.
6.. 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!)
7.. Always refrain from changing the steering angle with stern drive tilted in the "UP" position (especially when fitted with "rope/pulley" cable steering).
8.. 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.
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