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Prop nut torque

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The spec is not that important. In 50 years, I’ve never used a torque wrench…with no ill effects. Notice it states, 120”lb, but then states, if the holes don’t align, tighten till they do. Try that, on a bunch of motors…you’ll find the torque values cover a fair range.
 
In aviation we torque to the specified value then tighten to the cotter pin hole.

But I agree in this case it's not very important. 120 lbs/INCH is very little. Note that is inch, NOT feet. It equates to 10 lbs/ft.
 
I should have been more clear, I use a torque wrench where required, say head bolts on an engine rebuild. In this case you are only ensuring the prop is “snug” on the driveshaft. There is no gasket that requires partial crush to seal.
 
The inch pounds sounded low. I’ve seen as much as 120 ft/lbs + on some. Didn’t want the shaft to stretch going wide open on 70 degree top water and take out the lower unit. Must be a different design than others. I can go to the next hole for the cotter pin and will be plenty tight. Thanks again
 
Siskiwit said:
The inch pounds sounded low. I’ve seen as much as 120 ft/lbs + on some. Didn’t want the shaft to stretch going wide open on 70 degree top water and take out the lower unit. Must be a different design than others. I can go to the next hole for the cotter pin and will be plenty tight. Thanks again
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I really don't think the shaft will stretch from anything related to the prop- the shaft is splined, so the thread is only keeping the nut in place.
 
When warming up the engine for oil changes I heard the prop banging around and found the castle nut backed off a turn. That there would have at least caused a little damage. The boat has been in storage for the last few years so I’m guessing someone was pricking off.
 
Siskiwit said:
When warming up the engine for oil changes I heard the prop banging around and found the castle nut backed off a turn. That there would have at least caused a little damage. The boat has been in storage for the last few years so I’m guessing someone was pricking off.
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No Cotter pin?
 
There is no way a castle nut can back off a turn…unless some nitwit didn’t install the cotter pin. With the pin, the range the nut can turn is almost zero.
 
The only way that could happen was if the castle nut had never been tightened properly before the cotter pin was installed. They simply cannot turn more than a millimetre or two with a cotter pin in there.
 
One last question. I’m in the process of changing the impeller but forgot to take note of the direction of the rubber fins when reinstalling. I thought I took a pic but with my sleep deprivation I must have not. When looking down on the gear box which way do the fins go. Thanks in advance. Looking at it I’m inclined to say they should be arched to the right.
 
Looking at the old impeller the woodruff key stops at the top with a sealing surface on top with the fins going to the right so never mind.
 
The driveshaft turns clockwise, looking down, therefore the impeller also turns clockwise. There are several YouTube videos which show it wrong. They have the housing upside down, to show you, & turn the milled clockwise as they stuff it in. However,with the unit right side up, they’ve turned the impeller counterclockwise.
 
That’s kind of a dumb question…on one side of the circle, the fins will bento the right, but on the other side, they’ve turned the other way.
Don’t overthink it. Just remember the driveshaft always turns clockwise,when looking down from the top.
Visualize the housing as it sits in place. Hold the impeller underneath, & turn it clockwise…voila…that’s how it needs to go in the housing.
 
I should have just asked the shaft rotation. Like I say I don’t get much sleep and the brain doesn’t always put things together right.
 
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