Propeller installation - Help me feel more comfortable about my procedure

Jeremygavin

Well-Known Member
Mar 6, 2012
2,054
Cape Cod, MA
Boat Info
2011 520 Sedan Bridge
2016 Sea Ray 19 SPX OB
2019 Walker Bay Generation 340
Engines
Cummins QSM11s
Mercury 150 Fourstroke
Honda 40hp
I had the props pulled and had a few inches of pitch taken out of them this winter. I put the props on a few weeks ago. I am going in the water next week and I am still questioning my installation technique. I have seen Tony on Sbmar’s procedure and I tried to replicate it. The boat has 2 1/2” shafts and 28” 4 blade props. My procedure was to clean the keyway and key. Test fit the prop on the shaft without the key in place and mark where on the shaft it slide to. Then I put the key in and put the prop on and key didn’t bind so I think I am good there. I sprayed very little WD40 on the taper and wiped it down afterward.
I put the small nut on first and torqued it down as best I could. This is where I am a bit uneasy about the job. I had the shaft strapped off inside the engine room with a 3” rachet strap and had a socket on a 40” long 1” socket breaker bar. I had most of my sitting weight on the bar to tighten the nut but with the shaft binding on the strap, there was a little give till the strap tightened and stopped movement so I never got that hard stop like I would have if the shaft was locked down hard. The strap held so that I could put all my weight onto the bar and the nut didn’t get any tighter so who knows how much torque I was able to apply.
Then I covered the shaft threads with red lock tight and put the second (large) nut on and did the same procedure with cotter pin to follow. So question is, do you think I got it tight enough and I am good? I will be at the boat tomorrow wrapping things up and that will be my last chance to give it another go before I go in the water next week.
 
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I make a mark before removing props, something to compare to when I reinstall. I make sure the key doesn't interfere with the fit. If my props have been out for a tune up I use a fine grit lapping paste and lap the props. If I've just taken them off and reinstall I skip the lapping. It's really the fit of the prop hub to the shaft taper that's most important.

When installing nuts I just have some one, even my wife, put a foot against a prop blade. I put as much weight as I can on a 2' wrench and then hit the wrench with a 3lb hand maul. For the second nut I hold the first one with a wrench, someone puts a foot against it. I put as much weight as I can on the second wrench and hit it 3-4 time with the maul. That's my method of 'torquing'. I put everything together dry, no lube, no thread locker.

Any of the red Loctite products I think will require heat for removal. I'd stay away from that. If everything else is done correctly it isn't needed.

I'd say your good. My method doesn't hold the shaft rock solid either. That's the reason why I use the maul to give that extra quick sharp force.
 
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I just hope you never need to pull those props. Red loctite is intended for permanent installation. To get those nuts off you’ll need a torch to get the nuts hot enough (like over 500 deg) and then get the wrench on and un torque them. Hopefully that doesn’t distort the shaft locally.

The interference fit of the tapered shaft is what holds the props in place. Even if they were a little loose, the first time you throttled up on plane would seat the props. The cotter pin is there to preven the nuts from backing off.
 
I just hope you never need to pull those props. Red loctite is intended for permanent installation. To get those nuts off you’ll need a torch to get the nuts hot enough (like over 500 deg) and then get the wrench on and un torque them. Hopefully that doesn’t distort the shaft locally.

The interference fit of the tapered shaft is what holds the props in place. Even if they were a little loose, the first time you throttled up on plane would seat the props. The cotter pin is there to preven the nuts from backing off.
I haven’t had a problem getting nuts off with red Locktight in the past. As you said, I had to apply some heat but nothing too drastic that it would distort the metal. I have always used MAP gas with no problem. Hopefully it isn’t an issue when it comes time to take the props off.
 
Whenever work on a propeller is done the prop should be fit on the shaft with some machinist dye and then removed and the dye pattern inspected to ensure all of the dye is disturbed (the verifies there is full contact between the propeller bore and the shaft taper); this is an indicator that the taper on the shaft and taper in the prop match and there are no dings or bends that will prevent a proper fit. If it does not properly fit then it must be lapped in; have the propeller shop or your mechanic do this. Once that is done then the prop is fitted on the shaft without the key and snugged up with one of the nuts then scribe a line with a pencil or marker where the prop is on the shaft; this is done to ensure the key does not slide up and prevent the prop from fitting to the proper location on the shaft. A proper fit between the shaft and propeller does not require the nuts to be extensively tightened. You can place a soft wooden block between the hull and one of the blades and then tighten the thin nut to 300 - 400 lb ft for nuts that size. If you have a 24 inch long handle on the wrench and apply 150 - 200 pounds force on it then you are good. Many say not to block the propeller but when you look at the force placed on the end of a blade to tighten the nut it really is not that extensive. Put the thicker nut on, torque it the same as the thin nut then install the cotter pin and you are done. There is no need for any locking compound on the threads (I have never seen this done); in fact it is actually best to apply oil on the threads during the nut tightening. The simple fact that there are two nuts and the reason for two nuts is to provide a locking effect there is no need for any additional locking features.
 
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Whenever work on a propeller is done the prop should be fit on the shaft with some machinist dye and then removed and the dye pattern inspected to ensure all of the dye is disturbed (the verifies there is full contact between the propeller bore and the shaft taper); this is an indicator that the taper on the shaft and taper in the prop match and there are no dings or bends that will prevent a proper fit. If it does not properly fit then it must be lapped in; have the propeller shop or your mechanic do this. Once that is done then the prop is fitted on the shaft without the key and snugged up with one of the nuts then scribe a line with a pencil or marker where the prop is on the shaft; this is done to ensure the key does not slide up and prevent the prop from fitting to the proper location on the shaft. A proper fit between the shaft and propeller does not require the nuts to be extensively tightened. You can place a soft wooden block between the hull and one of the blades and then tighten the thin nut to 300 - 400 lb ft for nuts that size. If you have a 24 inch long handle on the wrench and apply 150 - 200 pounds force on it then you are good. Many say not to block the propeller but when you look at the force placed on the end of a blade to tighten the nut it really is not that extensive. Put the thicker nut on, torque it the same as the thin nut then install the cotter pin and you are done. There is no need for any locking compound on the threads (I have never seen this done); in fact it is actually best to apply oil on the threads during the nut tightening. The simple fact that there are two nuts and the reason for two nuts is to provide a locking effect there is no need for any additional locking features.

I understand the lapping that may be needed but these are the same props on the same shaft. I was under the impression that this was needed more on a prop and shaft that hadn’t been mated previously. It is still needed in this instance? I did fit the props on the shaft without the key installed and they rotated freely on the taper without any catching or binding. From what you are saying above and some of the other comments it sounds I shouldn’t worry about how tight I have the nuts and I may have made it a bit harder to take them off in the future.
 

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