Change the impeller on your OMC Cobra regularly -- generally once a year. Servicing the OMC Cobra impeller is very similar to doing so on most other outboard motors. The impeller sits inside the water pump housing on the top of the gear case. Replacing the impeller is a job that you can do with some basic tools in an hour or two.
Loosen the four screws underneath the top lip of the OMC Cobra outboard gear case with an open-end wrench, and remove the rubber plug from the side of the gear case with a flathead screwdriver. Remove the zinc screw from the side of the gear case with the flathead screwdriver, and let the gear case drop down from the exhaust housing about 3/4-inch.
Loosen the bolt between the exhaust housing and gear case with an open-end wrench, and slide the gear case away from the housing. Place the gear case in a vise, and remove the bolts on the top of the water pump housing with a socket wrench.
Lift the water pump housing off the top of the gear case, and take the impeller out of the water pump housing. Discard the old impeller and clean the inside edge of the pump housing with a clean cloth.
Take the metal plate and rubber gasket off the top of the gear case and clean the top of the gear case with a clean cloth. Apply a thin coat of marine grease around the inside edge of the water pump housing and on the top of the gear case where the pump housing sits.
Put a new rubber gasket and metal plate on top of the gear case, and insert the new impeller upside down into the water pump housing. Place a new O-ring on the inside lip of the water pump housing, and secure the pump housing assembly to the top of the gear case with bolts.
Remove the gear case from the vise, and slide the exhaust housing over the gear case with 3/4-inch space between the sections. Tighten the bolt between the exhaust housing and gear case with the open-end wrench, and slide the exhaust housing down onto the gear case.
Secure the zinc screw on the side of the gear case, and place the rubber plug over the zinc screw. Fasten the OMC Cobra outboard exhaust housing to the gear case with the nuts.
- To avoid injury, never attempt to replace the OMC Cobra motor impeller while the engine is still running.