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3YM prop shaft coupling bolts and propeller nut torque settings?

Dec 14, 2016
26
Beneteau 37 Chichester
Does anyone know the torque settings for re-assembling the gearbox coupling on the inboard end of the prop shaft and the propeller nut please? Its for a 3YM on a 2009 Beneteau Oceanis 37, but I guess the engine is more important than the boat.

In summary we require torques for three different nuts:
  1. The 24mm nut that holds the prop shaft coupling onto the prop shaft
  2. The 4 M8 bolts that hold the prop shaft coupling onto the gearbox coupling
  3. The nut that holds the propeller on
I have attached some diagrams/photos to help explain in more detail.
 

Attachments

dLj

.
Mar 23, 2017
1,047
Hunter 30 Snug Harbor, Lake Champlain
What are the bolts made from? 316 stainless steel? Other? Do you know?

dj
 
Oct 26, 2010
925
Hunter 40.5 Beaufort, SC
If you can't get the specific torque values from the specific manufacturer of the equipment (Bene) you can probably reach out to an industrial supplier of fasteners. For most applications, when there is metal to metal contact and no compressible gaskets are used the torque is often determined by the material and grade of the fastener, the fastener size, the thread pitch (course or fine) and whether the fastener is lubricated. A difference between the material of the cap screw and nut can cause significant torquing problems too. Be sure to use all of these factors.

Note that the assembly torque for 316 SS is less than and 18/8 SS fastener and both are considerably less than for carbon steel regardless of the grade of carbon steel fastener. Also note that once the torque is applied and the torque wrench as "clicked" to the final applied torque, going back to re-torque is somewhat of a crapshoot. DO NOT OVER TORQUE

By the way, since the shaft is not made by the engine or transmission manufacturer, they have little if anything to say about the torque to be used. That has to come from the manufacturer/assembler of the shaft coupling and shaft. If I were a betting man, since these are all metal to metal that they used the standard industrial guidelines from the fastener manufacturers.
 
Last edited:
Apr 8, 2010
1,259
Ericson Yachts Olson 34 Portland OR
While precision is a worthy goal, in about 40 years I have not observed a boat yard mechanic using a torque wrench for any of these fasteners. Of course I could have easily missed that part, not being present all the time work was going on.

I suspect that, like most of us with experience tightening (and occasionally breaking) fasteners, the folks turning the handle on the socket wrench have a pretty good 'muscle memory' for "snug", "tight", and final-eighth of a turn "tighter" , and "stop right there - that's enough".......

Hope you get a better answer!
:)
 
May 17, 2004
2,276
Beneteau Oceanis 37 LE Havre de Grace
While precision is a worthy goal, in about 40 years I have not observed a boat yard mechanic using a torque wrench for any of these fasteners. Of course I could have easily missed that part, not being present all the time work was going on.

I suspect that, like most of us with experience tightening (and occasionally breaking) fasteners, the folks turning the handle on the socket wrench have a pretty good 'muscle memory' for "snug", "tight", and final-eighth of a turn "tighter" , and "stop right there - that's enough".......

Hope you get a better answer!
:)
:plus:
I couldn’t remove the originally installed coupling bolts last time I tried, so I heartily agree. (They’re pristine; no signs of sticking from corrosion.). I suspect that the torque amount is specified only by how many wheaties the installer ate that morning.
 
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Oct 26, 2010
925
Hunter 40.5 Beaufort, SC
While precision is a worthy goal, in about 40 years I have not observed a boat yard mechanic using a torque wrench for any of these fasteners. Of course I could have easily missed that part, not being present all the time work was going on.

I suspect that, like most of us with experience tightening (and occasionally breaking) fasteners, the folks turning the handle on the socket wrench have a pretty good 'muscle memory' for "snug", "tight", and final-eighth of a turn "tighter" , and "stop right there - that's enough".......

Hope you get a better answer!
:)
Well said. The PO was asking for a torque spec and lacking any other info the standard tables are a good start if you want to use a torque wrench (for metal to metal). For the record, when its a Flex-gasket (with chevrons) using either a torque wrench or gap guage is really important. This in not a gasketed joint.

With all that being said, the length of a a standard set of wrenches will get you pretty close to "nominal" torque. Large wrenches aren't longer just because they have a bigger opening, they are longer because the bigger the fastener the more torque is specified for its tightening (per the standard tables). That's also why a 1/4 inch wrench is pretty small, to keep a wrench-head from overtorquing and a 3/8 is a little longer, and so forth. "Nominal" torque is the amount of force an experenced mechanic would use when tightening a fastener with a wrench of the proper size (with no cheater bars). The "problem" is that with a ratchet wrench the handle is the same length for most of them (1/4 inch drive are small, 3/8 inch drive is medium, and 1/2 inch drive is longer). With stainless steel you have to be pretty careful to not over-torque. I hold the ratchet at different points along the shaft (choke up if necessary) depending on the size of the fastener. If I wasn't going to use a torque wrench, I'd use the 3/8 drive ratchet for the 8M and the `1/2 inch drive for the 24M fasteners. I'd also choke up a little on the ratchet shaft to "account for the stainless" Make sure to apply counter-torque when you use a ratchet so as not to "twist" the nut since the torque is applied at a distance from the head/nut. In the times I have broken a bolt, it has almost always been when I couldn't get my hands in there to apply counter-torque or I was using a cheater bar.

By the way, the "breakaway" torque (torque to remove fastener) is frequently higher than the "running torque". Also, depending on how close you got to the maximum torque for the fastener size, if you go back a few days later you may get a little more movement even at the same torque setting because the fastener may "relax" some. It doesn't mean that you should retorque unless they tell you to.
 
Last edited:
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dLj

.
Mar 23, 2017
1,047
Hunter 30 Snug Harbor, Lake Champlain
So ball park torque for the 8 mm bolts would be around 100 inch pounds. Run them in lubricated. Stainless loves to gall.

I can't answer for your prop. I don't know enough about that specific application. I can tell you how I watched a guy do it years back on a boat. He lubed the cone for the prop, both shaft and prop. Then he tightened the bolt up on the prop, gave it a pretty good torque up, then relaxed it, and did it a second time. Then he put on the backing nut and tightened it up against the prop nut but I have no idea what kind of torques he was doing. He told me the first step of tightening and loosening was to make sure the prop seated correctly on the cone fitting. He said sometimes they move again after the first tighten.

Just as an aside, not using a torque wrench is better than you think. Here's a table from the machinery's handbook comparing accuracy of ways to tighten bolts... By feel ain't too bad really... ;)

1580500754053.png


dj
 
Oct 26, 2010
925
Hunter 40.5 Beaufort, SC
Wow dj. Good catch I had not seen that table before. Is that from the Mark's Handbook? I'll have to dig mine out if it is. Surprised that a calibrated torque wrench is that close to "by feel." I do just about all mine by feel except when there is a gasket involved and even then unless its critical like a head bolts I generally just do it by feel. So, by feel it is, especially since my torque wrench isn't calibrated anyway and I don't know many shops that calibrate their torque wrenches anyway.
 
Dec 14, 2016
26
Beneteau 37 Chichester
Thanks for all the thoughts and information, just what I needed. Beneteau claimed they didn't know the torques, which surprised me as I like to think the factory is a bit more sophisticated than "by feel" . I've done up a lot of bolts over the years, so I reckon I'll go by feel!