Mercruiser Alpha 1 Maintenance

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Mercruiser’s Alpha One outdrives have been around for over 25 years and have a proven history of being reliable when they are well maintained. Both the Alpha One “MR” and Alpha One Generation II are easy for owners to service with a few basic mechanical tools and a little effort. General maintenance includes servicing the propeller and shaft, changing the oil inside the unit and servicing the drive shaft.

Servicing the Propeller Shaft

  • At least once each season and anytime you suspect that the propeller may have run across a fishing line, remove the propeller and inspect the shaft. Bend the tabs on the locking tab washer to allow removal of the propeller nut. Once it’s off, the propeller and other parts will slide off. Remove any fishing line on the propeller shaft, apply a coating of grease to the shaft and replace everything in order. Don’t forget to bend two or three locking tabs into the position to hold the propeller nut in place.

Changing the Oil

  • Purchase two quarts of lower unit oil and an oil pump that fits quart bottles. The pump will come with a hose and special fitting to attach it to the unit. Trim the unit fully down. Two flush-mounted slotted screw caps are located on the left side of the unit. Remove the one at the top, then the lower one, which will allow the oil to drain out.

    Once completely drained, connect the fitting on the hose pump to the lower hole, insert the pump into the bottle of lower unit oil and pump in the new oil. The capacity is about 1-1/2 quarts so you’ll be into the second quart before the oil starts to flow out the top hole, signaling that the unit is full. If a lower unit oil reservoir is mounted on the engine, use some of the remaining oil to fill it.

Servicing the Drive Shaft

  • This is an annual or 100-hour service. It's messy and frustrating. If you use your boat enough to warrant learning to do it yourself, fine. Otherwise, spend the money to have it done by a professional.
    Purchase a lower unit gasket kit and a tube of M-4-C grease. The actual service on the drive shaft is simple. Slather some M-4-C grease on the drive shaft with special attention to coating the splines that slip into the engine coupler. Early model Alpha Ones have universal joints with grease zerks. A couple shots in each zerk and the maintenance is done.

    Removing the lower unit to get at the drive shaft is uncomplicated. Put the boat's shift lever in forward gear. If it is equipped with a speedometer, disconnect the rubber speedometer tube from the water pickup. Uncouple the ends of the hydraulic trim cylinders from the lower unit. Unscrew the six nuts that hold the lower unit to the boat and remove the unit. Service the drive shaft, remove the old gaskets and O-rings and replace them with ones from the kit.

    Here comes the potentially frustrating part. Inserting the drive shaft back into position is like pushing a rope. Persistence wins eventually, but it can be a long battle. Once it slides into its position, complete the reassembly.

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