Boats and Watercraft
Watercraft Engine Maintenance

How do you rebuild a water pump on a 1985 50HP Mercury outboard?

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Wiki User
2007-12-22 20:17:37

I'll run through the basic's for you here. First off, remove the

gearcase. Shift engine into forward gear and remove the trim tab.

The retaining bolt is located under the round plastic cover on the

rear of the exhaust housing, just over the trim tab. Remove the nut

located in the trim tab recess just forward of the trim tab

retaining bolt. Remove the three remaining nuts, one underneath the

anti-ventilation plate, and one on each side of the gearcase. Check

to make sure the speedometer feed tube, if so equipped, is

disconnected. Slide gearcase down and away from engine and secure

in a repair stand or other suitable repair fixture. Secondly,

remove the three nuts securing the water pump housing to the

gearcase. While turning the driveshaft clockwise, as viewed from

the top, pull up on the water pump housing cover. Slide the cover

and the rubber impeller up and off the driveshaft, be careful to

retain the impeller drive key, located on the driveshaft, inside

the impeller. Remove the impeller wear plate and upper and lower

plate gaskets. Clean all gasket material from water pump base.

Unless seals are to be replaced, leave water pump base in place.

Install new wear plate and gaskets, impeller and drive key. Inspect

the cup inside the upper housing for wear, replace if nessessary.

Spray some lube, WD 40 or equivalent, into upper housing, and on

the impeller. Slide the housing down the driveshaft until it makes

contact with the impeller. While turning the driveshaft clockwise,

push down on housing until the impeller is fully loaded into the

upper housing cup. Replace water pump housing washers and nuts,

snug, do not over tighten. Grease splines on top of the driveshaft

and the shiftshaft, also the mounting studs on the gearcase and the

exhaust housing. A small amount of lube on the water tube is good

also. Making sure you are in forward gear, the prop will turn

clockwise when you turn the driveshaft clockwise, slide gearcase

back on the exhaust housing. Use care to guide water tube into the

pump housing, also the lower shiftshaft into the upper. Reinstall

mounting nuts, trim tab and cap.

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