Prop Nuts Loose?!

Capt.Will

Active Member
Aug 15, 2016
148
Lake St. Clair
Boat Info
1997 Sea Ray 330 Sundancer
Engines
7.4 MPI Mercruiser Inboards
Vessel: 1997 Sea Ray Sundancer 330

Engine: 1997 7.4L Mercury Bluewater MPI

Transmissions: Hurth V Drives

Issue: Through out the season I inspected my props underwater and notice that my Starboard prop nuts always work themselves loose. Since I was working underwater during the summer I could only tighten so much. I have the cotter pin in place so they will not work themselves out too far and this problem does not seem to effect the prop position.

Is this common because of the clockwise rotation of the Starboard prop? Should I be tightening with a different method? Currently I am just stabilizing the prop and applying as much pressure on the nuts as possible with a wrench.
 
Vessel: 1997 Sea Ray Sundancer 330

Engine: 1997 7.4L Mercury Bluewater MPI

Transmissions: Hurth V Drives

Issue: Through out the season I inspected my props underwater and notice that my Starboard prop nuts always work themselves loose. Since I was working underwater during the summer I could only tighten so much. I have the cotter pin in place so they will not work themselves out too far and this problem does not seem to effect the prop position.

Is this common because of the clockwise rotation of the Starboard prop? Should I be tightening with a different method? Currently I am just stabilizing the prop and applying as much pressure on the nuts as possible with a wrench.

ours end up jammed so tight on the taper from forward motion that the nuts don't really do much past the initial setting

We use a giant 4' breaker bar and really wrench them down. The first time I reset the props I didn't do this properly and they backed off the taper when I put them in reverse to the point I could hear a clunk going into gear

my advice would be to really wrench them down with a giant bar and a good block holding the prop.
 
Consider a castled jam nut.

And often people reverse the nut order.
The THINNER nut goes on against the prop then the thicker nut is the jam nut.

https://www.getaprop.com/prop-tight-propeller-nut-kit-1.000-1.125

You can also stack bronze or Stainless washers between the jam nut and the key hole to prevent backing off. But they need to be tight not rattling loose.

castle nuts are preferred
 
Consider a castled jam nut.

And often people reverse the nut order.
The THINNER nut goes on against the prop then the thicker nut is the jam nut.

https://www.getaprop.com/prop-tight-propeller-nut-kit-1.000-1.125

You can also stack bronze or Stainless washers between the jam nut and the key hole to prevent backing off. But they need to be tight not rattling loose.

castle nuts are preferred

i have never seen this design…. First glance suggests if the nut wanted off… the cotter pin would get pulled in… then the nuts threads would run into the pin….. sort of defeats the castle part. Plus you are not wrapping the cotter pin around the shaft……. Just my opinion

I would stick with tightening the nuts thin one first

0CA352D3-016F-4A42-B763-AE8F2586DFA3.jpeg
 
Consider a castled jam nut.

And often people reverse the nut order.
The THINNER nut goes on against the prop then the thicker nut is the jam nut.

https://www.getaprop.com/prop-tight-propeller-nut-kit-1.000-1.125

You can also stack bronze or Stainless washers between the jam nut and the key hole to prevent backing off. But they need to be tight not rattling loose.

castle nuts are preferred

This! - This is exactly how it should be. Otherwise the nuts will loosen up over time, not matter how hard you tighten them. A castle nut is required for this application. One such as this will suffice: http://marinepropellers.com/propellers/index.php?route=product/product&product_id=163
 
This! - This is exactly how it should be. Otherwise the nuts will loosen up over time, not matter how hard you tighten them. A castle nut is required for this application. One such as this will suffice: http://marinepropellers.com/propellers/index.php?route=product/product&product_id=163
Ya but a castle won’t work on my shaft the nut slots won’t line up with the cotterpin unless you used washers to pull it back
I think you guys are putting too much thought into this…. Tighten the two nuts and be done….. I have never had a problem
 
Ya but a castle won’t work on my shaft the nut slots won’t line up with the cotterpin unless you used washers to pull it back
I think you guys are putting too much thought into this…. Tighten the two nuts and be done….. I have never had a problem
This. And if you want to easily keep an eye on it, when your done tightening, put a witness line on the nuts. Black marker won’t wear off and a quick look is all it takes. my props have been on since I changed cutlass bearings in ‘18. Haven’t touched them and mark was still there when I hauled a few weeks ago.
207259C3-813D-40B2-94A0-FBC10B7D9D7C.jpeg
 
The props should be lapped in when first installed. If this was done correctly and then tightened correctly you should not have any issues.
 
ours end up jammed so tight on the taper from forward motion that the nuts don't really do much past the initial setting

We use a giant 4' breaker bar and really wrench them down. The first time I reset the props I didn't do this properly and they backed off the taper when I put them in reverse to the point I could hear a clunk going into gear

my advice would be to really wrench them down with a giant bar and a good block holding the prop.

I will do that even more so than before. Thanks.
 
Thanks all for the input. Very much needed and I confirm that the thin nut is against the prop. I do wish a Castle Nut would work in this application but I don't believe it would be long enough to reach the cotter pin. I will make sure to really jam on that jam nut in the spring.
 
Thin nut first and when you tightened the thick nut up against it it puts the thin nut in one hell of a bind unless the prop is not completely seated on the tapper the prop the works forward over time which unbinds everything which lets things get even more loose.
 
Why can't you put a thin washer between the nuts then a castle nut would work??
 
In theory there should be no nuts required if everything is fitting correctly. If the nuts have loosened more than once you have other issues that need to be corrected. If this is the case then:
  • Disassemble and remove the prop from the shaft and inspect everything. Especially look for cracks and deformations.
  • Make sure there is no rotational play between the prop and shaft - the key and keyways are tight.
  • Cleanup the prop bore and shaft and using machinist dye check the fit between the prop and shaft.
  • Lap the prop to the shaft as required and re-check with the dye. After cleaning up the lapping compound/dye then re-fit the prop and scribe a prop location (index) mark on the shaft without the key installed.
  • Reassemble dry (no lube at all) and clean with the key installed and make sure the prop installs to the index mark.
  • Get new nuts and install the thin nut first (no lube here either). I use a 3 foot breaker bar and put all of my 172 pounds of weight against it. That's right at 500 LbFt for my 2.5 inch shafts.
  • Check that index line to make sure it remains as was after lapping. If it is not in the same location the prop is cracked and will require replacement.
  • Put the thick nut on and torque the same then install the cotter pin.
Done.
 
Last edited:

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