Jun 28

OMC Marine Engines and Sterndrives

OMC Stringer 800

Outboard Marine Corporation (OMC) developed and manufactured OMC Marine, Evinrude Outboards and Johnson Outboards. OMC also manufactured a variety of boats including Chris Craft, Lowe Boats, Princecraft, Four Winns, SeaSwirl, Stratos, and Javelin. OMC has since gone out of business but there design and engineering continue to prevail in many different marine applications. Most OMC applications can be seen in cruisers, runabouts, houseboats, and family boats. The most common OMC stern drives are the OMC Stringer Sterndrive (1962 – 1985), the OMC Cobra Sterndrive (1986-1992) and the OMC/Volvo Cobra SX (1993-1998). During the early production of the OMC stringers the 4-cylinder drives were known as the 400 series and the V6/V8 drives were known as the 800 series. The main difference of the two sterndrives is the gear size and shaft size in the gear case.
OMC had a unique design compared to their competitors, Mercruiser and Volvo, which involved supporting the engine and the sterndrive on the stringers of the boat hull instead of the transom. This design allowed for easier drive changes in water environments, sealing the the hull between the drive and the engine. This is how OMC Stringers got their name. The Mercruiser and Volvo sterndrive designs use U-joints to allow tilting of the sterndrive. This system uses a U-joint assembly that passes through the transom to connect the engine to the drive. Although this design worked well, any drive servicing required taking the boat out of water or it would flood. OMC used a ball gear setup to allow tilting, this design didn’t pass through the transom and therefore allowed for easy drive maintenance without flooding.

OMC Cobra

While OMC had come up with some very innovative ideas, in the long run, the design of the trim, shift and ball gears would be the torrential down fall of the OMC Stringer design. With Mercuriser and Volvo leading the competition in marine propulsion innovation, OMC decided to scratch the stringer design and in 1986 introduced the OMC Cobra. The Cobra utilized many of the innovative designs of its competitors with an OMC touch. The new engineering attracted the attention of Volvo and in 1993 OMC and Volvo entered into a joint venture and began developing a hybrid stern drive with the OMC Cobra transom plate assembly and the innovative new Volvo cone clutch outdrive. Sold as the OMC Cobra and the Volvo SX Drive, this drive had the best of both manufacturers. This system eventually turned into the Volvo Penta SX Drive when Volvo purchased the Plant and Rights to the OMC Cobra sterndrive system, a drive that is still utilized in today’s marine world.