1984 Mercury 90 hp 6cyl gear question

[Joe Kay]

I pulled the prop shaft to replace the shift cam. Before I put the lower unit back on the motor I have a question . I noticed that when in neutral I turn the drive shaft by hand in either direction, the prop turns. Is this normal?

 

[racerone]

Props do not turn in nuetral.-----Revisit the work done.

 

[Joe Kay]

The thing is I pulled out only what came with the bearing carrier. I didn't remove the drive shaft and forward gear and did not replace any seals except the shift shaft bushing. Everything from the bearing carrier to the cam follower came out together and I did not separate any of the parts, just took them out and put them back in one piece. Forward and reverse work as they should and in neutral I can hold the prop and stop it from turning when turning the drive shaft.

 

[Joe Kay]

I should clarify. When in neutral I turn the driveshaft clockwise the prop turns clock wise and when I turn the driveshaft counterclockwise the prop turns counterclockwise and the prop spins freely in either direction when I'm turning the prop and not the driveshaft. Anyone have an idea what's causing the problem?
Thanks for any help.

 

[jimmbo]

If you hold the prop shaft, can you still turn the driveshaft? BTW, if you rotated the driveshaft counter clockwise(viewed from above), you may have flipped a vane in the water pump, unless the pump is off.

 

[Joe Kay]

Yes if I hold the prop shaft, I can still turn the driveshaft. And I may have turned the driveshaft counterclockwise after I replaced the water pump. Also, after I replaced the water pump, the drive shaft became gradually harder to turn after it sat for a while. When I loosened the nuts the driveshaft turned more easily, but after time became very stiff again. I'm not familiar with the term "flipped a vane". Could you please explain?
Thanks

 

[jimmbo]

The impeller rotates in pump housing and the vanes/fins do bent to fit. But since the impeller is not centrally located in the pump housing the vanes are flexing as the impeller rotates. Reverse rotation of shaft can cause a vane to fold over in the reverse direction. Water is the waterpumps' lubricant. When you loosened the nuts, you reduced the squeezing of the impeller thus reduced the friction.

 

[jimmbo]

Here is an image, (poor quality) that shows the bending of the vanes, and what happens when engine is run out of the water

 

[Joe Kay]

Jimmbo
Thanks for the explanation. I'll check the impeller as soon as I get a chance, probably later today. If one or more vanes are flipped, that would explain why it becomes hard to turn the driveshaft by hand. Then I'll see if that stops the prop from turning when the driveshaft is turned in neutral. I appreciate your taking the time to help.

 

[jimmbo]

While a flipped vane could damage the impeller, would not make it more difficult to rotate the driveshaft. If you want to reduce the friction of the impeller when rotating the driveshaft by hand, when you reassemble the water pump, lube the impeller with a silicone or glycerin(K-Y Jelly) based, especially the top and bottom
Just make sure you install the impeller with the vanes curled the proper way. BTW the pic shows the view of the impeller looking down from above, backwards from what it will look like when you are looking into the pump bottom.

Flyingscott in the next post is dead on. Sometimes the prop will spin in neutral just because of drag from the oil

 

[flyingscott]

The prop turning in neutral is not uncommon as long as it freewheels and is not locked in either gear it's fine. The pinion gear is always engaged to the F/R gears so when you turn the driveshaft the prop shaft can turn. The shift dog is what does the actual driving of the prop shaft.

 

[Joe Kay]

Thanks for the input. The prop does turn freely in neutral and I can block the prop from turning while turning the driveshaft. So you have answered my question. I just wanted to be sure the prop would not turn with force when the driveshaft was turned by the motor. As for the water pump, there were no flipped vanes but the driveshaft is still hard to turn. My Seloc manual says to coat the impeller housing with a multipurpose waterproof grease. I used Quicksilver 24C but I didn't put any on the top and bottom of the impeller. I'll try the silicone or KY Jelly.
Thanks for the help.

 

[jimmbo]

That is Silicone grease, NOT Silicone sealer. I remember 20 years ago telling someone to apply Silicone to the trailer bunks to help loading, they glued the boat to the bunks:facepalm: