My 1987 175 HP V6 had a water pump failure. It began overheating immediately when given throttle. Took it apart to replace the pump. Pump housing was heat damaged and the impellor tips were burnt with rubber transfer to the housing. I have owned this motor since new and replaced the water pump many times without any problems. I did notice there was a lot of play in the drive shaft. Probably .025" up and down, and of course side to side as well. Don't remember this condition previously. Thought maybe the pinion nut came loose. took gear box apart, nut appears to be tight. Everything inside looks like new, no metal in the oil or grit in the case. The upper drive shaft bearing retainer nut was snug, but definitely not tightened to spec,., 100 ft lbs. Put it back snug, up and down play did not change. Any thoughts?
Make (of engine): Mercury
Model (of engine): 175 V6
Dismantled gear box except for removing drive shaft. It is the EZ shift lower unit.
Hi my name isXXXXX will assist you.
The play is normal as when the engine is in gear under a load there is no play. The gears push up when engaged pushing against the upper bearing. When there is no load the gears and bearings are relaxed and have play.
Doesn't seem right. The upper bearing outer race can move in the housing, up and down, plus the tapered bearing faces down. So the gears would have to pull the shaft downward under power, No? There were no shims on the top side of the bearing, don't know about the bottom, did not go that far. Shouldn;t the bearing retainer hold the outer race tight?
The driveshaft pushes up against the upper race which the retainer nut is torqued for.
See the race and bearing # XXXXX are tapered the driveshaft pushes the bearing into the race when under a load. When you put the engine in gear the driveshaft pushes away from forward and reverse gear. The shim # XXXXX is under the race which should not move as the nut is torqued down to spec for the clearance.
Ok, what you say makes sense, I see the bearing is opposite what I thought, tapered side up. Now, why would the water pump have such a heat related failure? worked fine last season, did not change it this year because of low hours last year. Worked ok initially this year, then began overheating under load until it finally overheated immediately with throttle. Thermostats are ok.
If you picked up something in the water that cut off water flow the impeller will melt. If the engine has been started with out water it will do the same. I have seen plastic bags get stuck on the lower unit cutting off water supply. I have seen people just crank the engine up for an instant to be sure it ran without water. Melting impeller is lack of water.
Never started motor without water. In fact, this year did not try motor before putting it in the water like i usually do, with the water adaptor on the lower unit. Thought maybe sea weed blockage or some thing, but pulled thermostats and everything clean as a whistle. Water always came out the pee hole, even when overheating. That's why I took it apart, seemed like something went wrong. Last question: Could I hook up a water hose to the water tube going up into the engine before I reinstall the lower unit to flush it and make sure there is nothing blocking the flow to heads. Motor is still in perfect condition and would like to keep it that way.
Yes we do that all the time when there is a heat issue with an engine. The other thing that can cause over heating the impeller is over trimming the engine. That usually only the case on high performance bass boats where the engine is real high on the transom. Sea weed can do this any kind of water restriction will cause the impeller to over heat.
Pleas post back if you have further questions......Thank you in advance ......Tan
35 yrs. experience. I/O, Outboard & Inboard, Complete engine repairs.Certified Technician