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Author Topic:   Tightening prop nut

Wet Foot posted 10-11-2006 06:02 PM ET (US)
When tightening the prop nut on my 125 HP Mercury 2 stroke, the tabs you bend do not align with the notches on the brass fitting, unless I continue to tighten beyond Mercury's spec. I needed to tighten an additional 5 foot-pounds. Is this ok? Should I reduce the torque a little instead. Is there a way to get the torque right on and have the tabs aligned?
davej14 posted 10-11-2006 06:25 PM ET (US)
I wouldn't worry about the extra torque. I do the same thing and it is better to be a little high than low.
The Judge posted 10-12-2006 01:10 PM ET (US)
you are supposed to torque a prop nut? News to me and I have never lost one.
an86carrera posted 10-12-2006 02:32 PM ET (US)
The only time torque anything is when assembling bearing caps, cylinder heads and flywheels.
Certainly not a prop with a lock tab washer or a cotter pin.
Never lost a prop either
Len
Robob2003 posted 10-12-2006 04:36 PM ET (US)
I was taught to tighten the prop nut snug then back it off if necessary to set the cotter pin in the castellated nut.
Also, there is no torque spec in my owner's manual.

Bob on Tampa Bay
fno posted 10-12-2006 05:56 PM ET (US)
Bob, your talking about old fashioned wheel bearing nuts. They needed (and still do) some end play in the bearing for when they heat up. A prop doesn't need any end play so the advise to haul on the nut till you find a notch is the way to go. It's better than a 3/4" thread on the shaft anyway. You will not do any harm with a hand wrench of any size to 1/2" drive.
jimh posted 10-12-2006 08:56 PM ET (US)
The procedure for installing the propeller usually includes a specification for the torque on the propeller nut. There is a good prior discussion on this topic:
http://continuouswave.com/ubb/Forum3/HTML/008218.html
--or--
http://continuouswave.com/ubb/Forum3/HTML/007285.html
Tom W Clark posted 10-13-2006 09:54 AM ET (US)
It is very important to tighten a propeller nut with a fair amount of torque. It is not necessary to use a torque wrench if you have a good sense of how much force is required to achieve 60, 70 or even 80 foot pounds of torque.
Robob2003,
You have it backwards. An acceptable technique would be to tighten the prop nut snugly with a wrench and then ADVANCE the nut to the first available slot or tab. Do not back it off.
It should also be mentioned that a propeller but should be checked after the boat has been run once; I often find that the nut needs to be tightened further. This is especially true of the FloTorq hubs in the newer Mercury and Michigan propellers. The added hub components do not necessary nest together perfectly the first time and can require a great deal of force to bring them together.
The reason why a propeller but must be tightened significantly, is that the propeller sees a great deal of force and must remain perfectly centered on the propeller shaft. Because the thrust washer is machined to fit the tapered shaft it will self-center so long as it is held tightly against it.
Mercury recommends a minimum of 55 foot pounds of torque. OMC (and I presume Bombardier) recommends 70 foot ponds of toque on the prop nut of their large outboard motors. In contrast my little 9.9 Johnson's propeller nut requires only 10 foot pounds of torque.
Robob2003 posted 10-13-2006 11:31 AM ET (US)
Tom,
I stand corrected but I guess it depends on your definition of snugly.
I usually have it as snug as it will go:-)
Bob on Tampa Bay

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Author	Topic: Tightening prop nut
Wet Foot	posted 10-11-2006 06:02 PM ET (US) When tightening the prop nut on my 125 HP Mercury 2 stroke, the tabs you bend do not align with the notches on the brass fitting, unless I continue to tighten beyond Mercury's spec. I needed to tighten an additional 5 foot-pounds. Is this ok? Should I reduce the torque a little instead. Is there a way to get the torque right on and have the tabs aligned?
davej14	posted 10-11-2006 06:25 PM ET (US) I wouldn't worry about the extra torque. I do the same thing and it is better to be a little high than low.
The Judge	posted 10-12-2006 01:10 PM ET (US) you are supposed to torque a prop nut? News to me and I have never lost one.
an86carrera	posted 10-12-2006 02:32 PM ET (US) The only time torque anything is when assembling bearing caps, cylinder heads and flywheels. Certainly not a prop with a lock tab washer or a cotter pin. Never lost a prop either Len
Robob2003	posted 10-12-2006 04:36 PM ET (US) I was taught to tighten the prop nut snug then back it off if necessary to set the cotter pin in the castellated nut. Also, there is no torque spec in my owner's manual. Bob on Tampa Bay
fno	posted 10-12-2006 05:56 PM ET (US) Bob, your talking about old fashioned wheel bearing nuts. They needed (and still do) some end play in the bearing for when they heat up. A prop doesn't need any end play so the advise to haul on the nut till you find a notch is the way to go. It's better than a 3/4" thread on the shaft anyway. You will not do any harm with a hand wrench of any size to 1/2" drive.
jimh	posted 10-12-2006 08:56 PM ET (US) The procedure for installing the propeller usually includes a specification for the torque on the propeller nut. There is a good prior discussion on this topic: http://continuouswave.com/ubb/Forum3/HTML/008218.html --or-- http://continuouswave.com/ubb/Forum3/HTML/007285.html
Tom W Clark	posted 10-13-2006 09:54 AM ET (US) It is very important to tighten a propeller nut with a fair amount of torque. It is not necessary to use a torque wrench if you have a good sense of how much force is required to achieve 60, 70 or even 80 foot pounds of torque. Robob2003, You have it backwards. An acceptable technique would be to tighten the prop nut snugly with a wrench and then ADVANCE the nut to the first available slot or tab. Do not back it off. It should also be mentioned that a propeller but should be checked after the boat has been run once; I often find that the nut needs to be tightened further. This is especially true of the FloTorq hubs in the newer Mercury and Michigan propellers. The added hub components do not necessary nest together perfectly the first time and can require a great deal of force to bring them together. The reason why a propeller but must be tightened significantly, is that the propeller sees a great deal of force and must remain perfectly centered on the propeller shaft. Because the thrust washer is machined to fit the tapered shaft it will self-center so long as it is held tightly against it. Mercury recommends a minimum of 55 foot pounds of torque. OMC (and I presume Bombardier) recommends 70 foot ponds of toque on the prop nut of their large outboard motors. In contrast my little 9.9 Johnson's propeller nut requires only 10 foot pounds of torque.
Robob2003	posted 10-13-2006 11:31 AM ET (US) Tom, I stand corrected but I guess it depends on your definition of snugly. I usually have it as snug as it will go:-) Bob on Tampa Bay