Yamaha lower unit gear lube is drained by removing the lower drain screw first and then the upper plug vent to allow air in. On most models, both plugs are clearly visible on the lower unit, but on models with low water pickups, the forward pickup will need to be removed to access the drain plug. Use a properly sized screwdriver assisted by a wrench if necessary to loosen these screws which should be pretty tight. An impact driver and hammer may be needed depending on who serviced your engine last. The drain screw has a magnetic tip, so inspect the plug after removal to see if heavy deposits exist. Some fine shavings are normal, but chunks or a large quantity of metal is cause for further inspection. Have a drain pan and extra rags handy as gear lube will begin running down the skeg as soon as you remove the upper vent plug. Be sure to collect the fiber gaskets from both plugs after removal, as these are not reusable and should be discarded.
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Allow several minutes with the engine tilted all the way down to fully drain the old gear oil. Like your engine oil, inspect the spent oil for evidence of water intrusion or other contamination or metal. If you have purchased one of PartsVu’s handy lower unit oil change kits you will already have new gaskets, oil, and a pump. Screw the pump into the lower drain hole and then connect it to the quart of Yamalube gear oil or HD gear oil depending on your model. Begin pumping oil into the lower unit until oil begins to flow from the vent plug at the top. Stop pumping and wait a few minutes for all the air bubbles to work themselves out of the gearcase. After this brief pause, pump a few more pumps until clean gear oil without bubbles is flowing from the vent plug. With a fresh fiber gasket in place, install and torque the top vent plug. Unscrew your fill hose from the lower drain plug and quickly swap in the lower drain plug with a new gasket. Torque to spec and re-install the lower water pickup screen if applicable.
Start a Yamaha 100-hour service Step # 1 - Oil Change
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