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