Gotta tighten prop nut - how to hold shaft?

ZZ13

ZZ13

Well-Known Member
Nov 25, 2009
5,328
Lady's Island, SC
Boat Info
2001 400 Sedan Bridge
Engines
Cummins 450 Diamond
My port prop (straight drives) has minuscule rotational movement. Just a tad but can see it move. I'll be tightening it in the water. Can I hold shaft from rotating by using a bar on the transmission coupler nuts rather than blocking the prop to the hull? Or will that put too much rotational torque on the length of the shaft when I tighten down the prop nut.
 
ZZ13 said:
My port prop (straight drives) has minuscule rotational movement. Just a tad but can see it move. I'll be tightening it in the water. Can I hold shaft from rotating by using a bar on the transmission coupler nuts rather than blocking the prop to the hull? Or will that put too much rotational torque on the length of the shaft when I tighten down the prop nut.
Click to expand...

Put it in gear.
 
2x4 about 2’ long, span it between the rudder post and the strut. On our boats it works well because the 2x4 crosses the prop about half way between the blade top and the hub while keeping the 2x4 close to the hull. This is how I do it.
Or You could hold the shaft coupler by placing a wrench on the head of one of the bolts, position it so that when you tighten the prop nut, the wrench backs up on the floor. Probably have to have a helper hold it on so it doesn’t slip off while you get ready to tighten.
Check out the picture of removing the coupler nut in the 40db thread back in late April/early May. I used a pry bar and longer bolts just because I could, but it held the shaft solid while removing and installing the coupler.
 
CaptRonn said:
Put it in gear.
Click to expand...
Sounds scary. ZF 280 transmission. Have you done it this way or seen it done?

My diver in Ft Pierce that has taken off and installed my props several times uses two 4x4 pieces to block the base of the prop against the hull. I'm trying to find something easier to do. The nut wont be turned very much. Just a tad.

I do have a monster pipe wrench for the tightening part.
 
my3sons said:
2x4 about 2’ long, span it between the rudder post and the strut. On our boats it works well because the 2x4 crosses the prop about half way between the blade top and the hub while keeping the 2x4 close to the hull. This is how I do it.
Or You could hold the shaft coupler by placing a wrench on the head of one of the bolts, position it so that when you tighten the prop nut, the wrench backs up on the floor. Probably have to have a helper hold it on so it doesn’t slip off while you get ready to tighten.
Check out the picture of removing the coupler nut in the 40db thread back in late April/early May. I used a pry bar and longer bolts just because I could, but it held the shaft solid while removing and installing the coupler.
Click to expand...
I like the 2x4 approach. I'll try that. I thought of that but worried the strut and rudder post wouldn't like the lateral force. Guess I am over thinking it.

Is the 4" width of the 2x4 oriented horizontal or vertical?
 
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ZZ13 said:
I like the 2x4 approach. I'll try that. I thought of that but worried the strut and rudder post wouldn't like the lateral force. Guess I am over thinking it.
Click to expand...

they don’t like the lateral force, so keep the wood close to their bases, close to the hull. If you think you might do your own prop work in the future, buy a cheap Pittsburg tools 24” adjustable (crescent) wrench the next time by Harbor Freight. I hate chew marks on my nuts. :)
 
ZZ13 said:
Sounds scary. ZF 280 transmission. Have you done it this way or seen it done?

My diver in Ft Pierce that has taken off and installed my props several times uses two 4x4 pieces to block the base of the prop against the hull. I'm trying to find something easier to do. The nut wont be turned very much. Just a tad.

I do have a monster pipe wrench for the tightening part.
Click to expand...

Not sure what's scary about it, unless you are putting extreme amount of torque which will turn the engine over.
 
CaptRonn said:
Not sure what's scary about it, unless you are putting extreme amount of torque which will turn the engine over.
Click to expand...
The gear requires the engine running to provide the hydraulic pressure to engage the clutch pack; but, then the engine will rotate the shaft as it needs to be running to engage the clutch pack..... Otherwise the clutch packs are disengaged and the shaft will freewheel. Marine transmissions do not engage and disengage gears like an IO or automobile manual transmissions do but rather engage and disengage clutch packs like an automobile automatic transmission.
 
Working under water is difficult. Get a wood block between a blade and your hull and arrange it so it will not tend to roll and put a bending force on the blade tip.
It's concerning when props become loose as you don't know if it was installed incorrectly, the nuts are loosening, or the shaft material is failing. 99% of the time the prop was installed incorrectly.
Get a strap on the prop and secure to the strut so should the shaft shear off you won't loose the prop.
You probably know this but thin nut against the prop and thick nut against the thin nut...
Remove the cotter pin and the first nut. Tighten the thin nut to the prop to spec and mark where one of the nut flats is relative to the prop then loosen and tighten again; if that mark realigns you are done. Then the thick nut and cotter pin.
 
ttmott said:
Working under water is difficult. Get a wood block between a blade and your hull and arrange it so it will not tend to roll and put a bending force on the blade tip.
It's concerning when props become loose as you don't know if it was installed incorrectly, the nuts are loosening, or the shaft material is failing. 99% of the time the prop was installed incorrectly.
Get a strap on the prop and secure to the strut so should the shaft shear off you won't loose the prop.
You probably know this but thin nut against the prop and thick nut against the thin nut...
Remove the cotter pin and the first nut. Tighten the thin nut to the prop to spec and mark where one of the nut flats is relative to the prop then loosen and tighten again; if that mark realigns you are done. Then the thick nut and cotter pin.
Click to expand...
My props have been off probably 6 times in the seven years I've owned the boat. Two different yards and a diver have done it. Every time each one put the thick nut against the prop and the thin nut as the outer nut. That's the way it is now.

I noticed the prop was loose after I reeled up a crap pot with that prop. Couldn't tell you if that did it or if it was loose before. Maybe there was slack between the prop nut and the lock nut and reeling the rope in spun the prop nut back just a hair. I don't know.
 
ZZ13 said:
I've read that and other articles on the subject in the past. I never really concerned myself about it since I've seen it done both ways. Maybe I'll bring it up with my local yard. My diver explained why he does it opposite. Basically for him it's easier that way for in-water installation.
Click to expand...
The thin nut is required first. The reason is so more threads on the shaft share the stress.
 
ttmott said:
All Hail Tony Athens; but he is wrong completely on installing the nuts from several technical aspects. It's all your decision however...
He is 100% correct on the prop to shaft fitup however.
Click to expand...
Just passing data. No opinions by me in any of my posts. I'll talk to my yard. I'll probably now do a short haul by them to correct the problem. Going to try a quick tightening by myself for the short cruise over to the yard.
 
ZZ13 said:
Just passing data. No opinions by me in any of my posts. I'll talk to my yard. I'll probably now do a short haul by them to correct the problem. Going to try a quick tightening by myself for the short cruise over to the yard.
Click to expand...
If you are going to do a short haul then pull the prop and check it's fit.
 
Just got out of water. It's done. Jam nut was loose and prop nut was loose. Was super easy to turn the nut with one hand on my pipe wrench to tighten. Then I tightened the jam nut. Jam nut alignment was noticeable further around on the main nut than before. Flats of both nuts are now perfectly in line (Jam nut was a tad counterclockwise before). Certainly no torque measuring was done so I will keep checking every week when I dive to clean bottom and will have yard install nuts the right way at haul.
 
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