Prop Install

[Beckytek]

While I was at the boatyard today my neighbor was installing reworked props he bought from a prop shop. I asked him if he lapped the prop in first and he said no. He told me one of the props was modified from a 2" shaft to work with his 1 3/4" shaft by inserting a plastic bushing in the hubb. How can you lap that arrangement? I was wondering if the only thing that holds the prop on, is the good connection at the taper, how is it going to hold with a plastic insert between the metals. Does anybody know if this is normal? I can't imagine installing a prop like this on my boat. He is a charter boat captain that fishes the canyons of New Jersey all the time. What's up? Ron

 

[Genesis]

Yes, this is quite legitimate. I had a set of props and shims of this sort and they worked fine. You need to cut a step key for them.

The shim is a nylon-type material and it deforms under pressure. Once torqued down it is an extremely solid connection and doesn't slip.

Its not my preference for obvious reasons but if you ever damage a bore on a prop its an option, or if you have a prop with a hub size that is off by one and want to use it, it works.

 

[Brian Degulis]

What you have to watch with the bushings is the key. Most of those kits are supplied with bronze keys. Because the key is much higher and stepped it should be stainless because the bronze can shear.

Brian

 

[Genesis]

If a prop is correctly installed the key takes no load and will not shear. It is there only as an alignment and installation device on a morse taper joint.

Even with the shims, it will not take load at all if the wheel is properly installed.

If you take load on the key (shimmed or not) you are asking to break the shaft. Using a stainless steel key (beyond the much higher machining hassle and expense) simply upps the odds of a shaft fracture in the event of improper installation of the prop.

 

[Maynard Rupp]

In the new Hatteras literature they show their new prop key system uses a round bar with a half round cut on both the prop and the shaft. This is to reduce the chace of a stress crack in the shaft from the sharp edged cut for a standard key. Good idea eh?

 

[Beckytek]

I learn something new everyday at the forum. Thanks

 

[Bob Bradley]

If you take load on the key (shimmed or not) you are asking to break the shaft. Using a stainless steel key (beyond the much higher machining hassle and expense) simply upps the odds of a shaft fracture in the event of improper installation of the prop.

Trust Karl on this. My wallet still throbs as a result of an improperly (no pun intended) installed prop. Somewhere between Branford and New Haven, there is a $3000 prop on the bottom of Long Island Sound. The sound it made while encountering the bottom of my boat is not a sound I wish to hear again.

 

[John Dickson]

Could you please describe the process of lapping?
thanks

 

[Nonchalant1]

Go to NAPA and get course valve grinding compound and some Prussian Blue. Clean the shaft taper and the prop hole well. Put valve grinding compound on the shaft enough to get a light coating all along the taper (doesn't matter much because it'll goosh out if there's too much). Put the prop on the shaft without the key and push it all the way up against the taper. While pushing it on, turn the prop by hand and it goes around the shaft while the shaft does not turn. This grinds the softer bronze prop much faster than the hard stainless shaft and matches the taper of the prop to the shaft. This is important because it's the close fit taper that keeps the prop from slipping underway, NOT the key. Turn it 100 times around and then remove the prop and clean the prop and shaft very well (important). Rub the Prussian Blue on the shaft to get a light coating. Put the prop back on, push it on hard and turn like you were lapping one or two turns. Now pull the prop straight off without turning much and look at the blue on the shaft. You can see the area of good contact by the blue in nice concentric lines around the shaft. There will probably be areas where the blue looks untouched or confused patterns instead of concentric rings, and those are where the taper does not match. You want to do this over and over until the matched taper is 80% of the total taper. Lots of cleaning each time. The final cleaning should be very thorough.

To install, put the prop on the shaft DRY (yes, dry), without the key and push and turn it until it goes all the way on. Mark the shaft with a magic marker where the prop went all the way on and that's at least how far it should go when finally installed. Now back it off a little, match up the keyways and push the key in from the back. Never put the key on first or the prop can ride up on the3 key and not get fully installed. With the key in and the prop on, put on the big nut first and torque it up HARD (no I don't know the correct torque, I just use a huge socket with an 18 inch handle and a 2 ft. cheater pipe and crank it up hard, with a wood block against the prop and hull. Check to make sure the prop went up to at covered your previous mark. If it didn't, the key is binding. Now remove the big nut, install the thin nut and torque it less hard than when installing the prop, then put the big nut back on and torque it harder than you did for the thin nut to lock them together. Hard torque here is OK, but you're just locking them together now, so I don't use the cheater bar. Install a new cotter pin and you're done.

Lots of discussion about lube or dry, but dry is correct.

Lots of discussion about big nut first or small nut first, but it probably doesn't matter as long as you use the big nut first to do the original seating torque of the prop (because you want more threads on the nut to take the torque). Some people just install the thin nut second and leave the big one seated against the prop.

Doug Shuman

 

[Brian Degulis]

Talk to an expert like General Prop in Bradenton FL. They can tell you all about the nylon bushings and keys shearing there is no precision fit with nylon to metal to nylon that's why they shear.


Brian

 

[John Dickson]

Doug

Thanks for the instructions! Perhaps they should be transferred to Freq. Asked Questions.

John

 

[mike]

FWIW, follow this advice and be happy .... Mike

Propeller installation / Big Nut vs. Little Nut

--------------------------------------------------------------------------------
By Tony Athens
--------------------------------------------------------------------------------

To answer a common question that seems to pop up quite often and without getting too technical, you'll find that the thin nut is supposed to go on first and torqued to something less than full spec.. The BIG nut then goes on and is brought up to full torque......That's what the good engineering will say.

BUT, from the practical standpoint (sometimes) and what seems to be done out in the field, it's a different story....I think I could write a small book on proper propeller installation, as there are many principles involved that the typical "yard employee" doesn't understand and, in the 20+ yrs I've dealt w/ shafts, props etc., I've run into some doozy examples of poor prop installation.
I've seen more than one vibration problem solved when the key was properly re-fitted so the prop didn't ride on it.. I've seen "hot props" put on only to see the prop not come off without pulling the shaft (or worse).. A bronze prop that's been laying in the sun ( a "hot prop") may not come off when you need to pull it with normal methods.. And, of course, I've seen many a prop come loose, only to lose it, and many a broken shaft, which I believe, in many cases, was due to the prop coming loose and working on the keyway.

This has led me to develop my own protocol for installing props. Some readers may already know some of these suggestions, but I'll go over the most important ........

First things first: The Keyway - On both the shaft and the propeller I always make sure there are no sharp corners or burrs. Although proper machining techniques would dictate a radius in the corners of the shaft keyway, this is not always the case. But, all keys do need a radius on all corners so as to prevent riding in the corner of the keyway. This is besides the grinding that may be necessary for a "slipper cut" key.. Always be sure that the key you have selected slides easily through the propeller keyway and into the shaft keyway. Yes, there are some who think that it should be tight; I disagree 110%... Just about all new props require some light filing / deburring in the keyway so the key will slide smoothly with no binding. I normally use a good, single cut file to dress the keyways/edges and my belt sander to radius/grind key stock.

As far as fitting the prop to the shaft, this should always be done BEFORE the key is used to ensure that the propeller and the taper are properly matched. A light spray of lubricant or smear of grease will allow you to install the prop and spin it on the shaft without the key to find out if there are any "catches." Many times you'll feel one keyway ride or catch on the other due to the imperfections of the machining. This is where lapping (filing) the two together will pay dividends. This can be done with standard light to medium grit valve grinding compound and only takes a few minutes to get a 95+% fit. It will also show you where your problem areas are...Larger props are sometimes undercut in the middle of the taper allowing only the small end of the taper and the large end of the taper to make contact with the shaft..

After the prop goes on the shaft properly without the key, a small mark or reference should be made as to how far up the prop goes on the taper before the key is installed. This reference point will guide you when the key is finally fitted to be sure that the propeller is fully seated on the taper and not riding on the key. This is the most common mistake in prop installations that I have seen.

As to the subject of lubrication between the prop key and taper, most yards seem to lean towards a "never-seize" type compound. Personally, I use a combination of Rector Seal #5 with a light spritz of WD-40. And, I use it liberally. Your choice on this, but the idea here is to fill any and all voids between the prop and shaft, allow the tapers to go together (slide) properly, thus keeping any crevice corrosion to a minimum.. And, the only way you are going to get that NUT really tight, is to have a lubricant on the thread and in between the nut face and the prop.

When it comes to the nuts and tightening, I'm sure only a few may agree with me. I know the yards frown on my technique. But here goes..(and I've been doing it successfully for years and years). .After all the above has been accomplished (and it doesn't really take very long unless we have a non-standard keyway), I always put the big nut on first with plenty of lubricant and sometimes a custom washer between the big nut and the prop. Depending on the shaft size, torque will vary from maybe 40-50-ft lbs on a 1" shaft to 100++++ of ft-lbs on a 2-1/2" shaft. Wait for 5 to 10 minutes after the first tightening to allow the excess lubricant to hydraulic out of the fitting between the prop / key / nut / shaft, etc. I then retighten the big nut again. Now comes my solution to prop nuts staying put, I clean the threads with spray brake-cleaner or whatever I have handy, smear a nice heavy dab of MarineTex or other common epoxy on the threads of the shaft (second nut only), and tighten up the small nut to something applicable to the shaft size. 3M 5200 or a similar high-strength urethane will also do an Okay job if it's allowed to cure first. But, an epoxied nut "don't go nowhere", (until you want it to). And it does what it does quickly.. And then, when you remove it someday, it seems like the worlds best self-locking nut as it comes off. When I'm in the yard working on big shafts, I'll sometimes use a propane torch to soften the epoxy/5200. Don't forget, it's not at all uncommon to warm a properly installed prop before you remove it anyway.. Makes life easy most of the time.

As for cotter pins, all they do is catch monofilament line as they will not stop a prop nut from coming loose, unless of course, they're used with a properly fitted castellated nut. A much better trick to ensure the security of the rear prop nut mechanically is to cross drill it thru a hex corner, and properly safety wire it through the cotter keyhole ala "aircraft style."

I've touched on a few points here. From doing this type of work for many years and also seeing (first hand) many problems resulting from the lack of understanding some simple concepts involved in the installation of propellers, I hope this will help some our readers. Big Nut or Little Nut first doesn't seen to matter to me IF the prop is fitted properly and the NUT's are tightened to spec. And with a little glue or safety wire, I never worry.

P.S. A left hand prop is (usually) less likely to come loose than a right hand prop.. Ever wondered why??

 

[Trojan]

Well you have the first part correct. But you will never loose a nut when they are properly installed and torqued. It was covered in this forum last year to a great extent. Nuts install goes like this. Big nut on to torque (seating the prop to the shaft taper) then off, little nut on snug then big nut on and tightened to torque. A properly installed prop requires no nuts to hold it to the shaft. Nothing should be put on the shaft or prop bore. It should be super clean and dry. The taper fit is the only thing that is required to secures the prop to the shaft. Epoxy is never required to hold the nuts on. What did we do before epoxy the last 100 years. That is the reason for the torquing of the nuts. Of course you can do as you like and I don't mean to pick on you. The cotter pin is used to keep the nuts on the shaft should they ever come loose.

BILL

 

[mike]

FWIW, pls note the info on my post is authored by Tony Athens from Boatdiesel.com, is has a very reputable re-power company on the west coast. He has worked on many hundreds of commercial and private boats over the years, and his excellent results speak for themselves. I have followed his advice with excellent results.