Many boat owners with older inboard/outboard or stern drive motors consider the possibility of converting to outboard motors when forced to re-power their craft. Most people that switch are looking for the extra space inside the stern along with a sizable weight reduction. This conversion brings considerable challenges with it, including fiberglass and structural work. Two of the biggest considerations are distancing the lighter outboard motor further back to maintain even weight distribution along with the entirely new motor controls and rigging.
Things You'll Need
- Sling and engine crane
- Outboard spacer brackets
- Fiberglass repair materials
- Interior refurbishment materials
- Mechanic's tools
- Woodworking and fiberglass tools
Disconnect and remove the I/O stern drive lower unit. This will leave a large opening in the transom.
Disconnect the battery and remove it from the boat. Disconnect all engine electrical cables and wires. Tape them off temporarily before opening the fuel system. Drain the fuel lines and disconnect them. Drain the inboard engine coolant if applicable and disconnect the coolant lines.
Remove the water-cooled exhaust connections. Disconnect any mechanical linkages connected to the engine. Use a sling to attach the engine to an engine crane. Unbolt the motor mounts and hoist the old engine out of the boat.
Strip and clean the exposed inside hull bottom. Temporarily position the new outboard extension bracket onto the rear of the stern. The extension bracket will need to transfer thrust into the same place the original stern drive did, or the transom will need to be bolstered to bear the motor loads. An experienced boat builder can provide assistance with this re-design step.
Use 3/4-inch thick marine plywood to reinforce the inside of the transom. Apply two layers of 6-ounce fiberglass cloth over the plywood using polyester resin to reinforce and protect it. Apply two extra reinforcement layers of fiberglass cloth in the corners between the transom, the sides and bottom of the boat. Cut plywood to fill the old sterndrive opening from the outside and cement it into the cavity with resin. Then apply a layer of 6-ounce fiberglass cloth to the entire outside of the transom and finish it with a top layer of gel-coat resin to match the color of the boat.
Drill installation holes in the transom for the new bracket. Make at least three new through-holes in the transom for the motor umbilicals and steering. Use a hydraulic steering system for a cleaner installation.
Line all the holes in the transom with sealant and install rubber liner boots for the motor umbilical openings. Apply sealant to the transom bracket as required and bolt up the new bracket.
Mount the new outboard motor. Install the new motor control center at the helm station. Connect the fuel line from the tank to the motor with an extra in-line filter inside the boat. Mount a new battery and connect all inter-wiring between the control, the boat's electrical system and the motor per manufacturer's instructions. Fill the motor crankcase with oil or fill the reservoir for direct-injection two-strokes. Test the entire electrical system for correct operation and integrity. Seal all openings created for wires and cables.
Place an earmuff water connection on the outboard's water intake and turn on the water. Start the motor. Let the motor run and check charging circuits, trouble lights and indicators.
Tips & Warnings
- Install outboard power that is about 25 percent higher than the I/O engine removed because of the torque curve differences between the two types of engine.
- The outboard motor will have to be up to a couple of feet further back because of the greater weight and location of the old I/O engine.
- Double-check all fuel and electrical connections to prevent fires.
- Photo Credit boat image by michele goglio from Fotolia.com
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