prop installation

[Serenity]

I have been led to believe that you should not lubricate the shaft when installing the prop. I purchased a a different style puller, and Acme reccomends that you do lubricate the shaft. Any thoughts?

[jleonard]

This was JUST referred to in the thread below, but I pasted it here. I'm sure Tony wouldn't mind.



Propeller installation / Big Nut vs. Little Nut

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By Tony Athens
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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 with 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??

[Serenity]

Thanks. I hope that this is the final chapter of the "book". The P.S. part, the left hand prop turns opposite of the threads therefore becoming more tight.

[Serenity]

According to the article, the author reccomends that the shaft be lubricated with Rector Seal #5 and WD-40. I have spoken to the local prop guy that I purchased my prop from and his thoughts are NOT TO lubricate the shaft. I spoke to the factory, Acme that made the prop and they also do not reccomend lubricating the shaft.
Last year I replaced my old 14 year old prop with a new three blade. I must admit, it was a bear to get off. I installed the new prop with no lubrication. I pulled it off yesterday with help from a prop puller, heat, liquid wrench and a big hammer. The reason why I am pulling the prop off is to achieve the 3900 rpms that Yanmar feels the 315 should hit at WOT. I am 100 short. This should do it.
Instead of a POD system, we should have variable pitch props that we can control from the helm. We had it in the Navy, but then again we were turning a 20 foot wheel.

[jleonard]

My only comment about lube vs no lube is that the prop shop sells , inspects, reconditions props. Tony Athens installs props and lives by how good of a job he does with that installation.

[meridian]

Are you changing props? 100 rpm? That gets lost in the decimal points. Have you checked your RPM's with an digital tach? You can get them for less than $30.

[Serenity]

I replaced my 13 year old prop with a new Acme prop in January of 2011. After attending a 3 day seminar at Mack Boring, they were emphatic about the 315 hitting 3900 rpms at wot. On the first installation, I could only hit 3700. This was verified by a digial Aetna Tach and Photo Tached. I had Serenity hauled, brought the prop to the prop shop, it was tweaked and re-installed the same day. The best I could get was 3800. We decided to wait till the season was over to have it tweaked one more time.
I have A $30,000.00 engine and I want it set up to run as per the specs. From what I have read on previous posts, the earlier 6LP's had over propping issues which affected the performance of the engine. For $200.00, for me it is worth it. I will make it back in decreased fuel consumption.
I had read the post about lubricating the shaft when putting the prop back on. I checked with the prop guy and the manufacturer Acme, and they both reccomended do not lubricate. I have been boating for 40 years and most yard mechanics are excellent and know quite a few tricks of the trade. If it works for you, great. When someone is banging me $125.00 an hour, I want to be sure it is correct and according to manufactuers specs. They built it, not the mechanic.
Trust me, I am not anal. I have convinced my wife that I am bi-polar. When I purchase that additional gadget for the boat, I blame the other "guy". I want the engine to be at its peak. I intend to do off-shore fishing and extended cruising in 2013 and I want Serenity to be fit.

Happy boating and have a great Holiday

[jleonard]

Are you changing props? 100 rpm? That gets lost in the decimal points. Have you checked your RPM's with an digital tach? You can get them for less than $30.

100 rpm is a big deal.

[hetek]

Are you changing props? 100 rpm? That gets lost in the decimal points. Have you checked your RPM's with an digital tach? You can get them for less than $30.

Ditto on this.

I talked with an old school diesel guy and I mentioned that I was 150 RPM short of WOT. My Lehman is spec'd for 4000 RPM WOT and all I could get was 3850. "Should I get the prop repitched for that extra 150 RPM?"

His reply: "You're not only in the ballpark... You're in the infield. Leave it alone!".

Told you he was an old school diesel guy.

[jleonard]

Naturally aspirated? Planing hull or displacement?
Makes a difference. The modern lightweight turbocharged diesels don't take very well to overloading.
But it's your boat and you pay the bills.

[Serenity]

In regard to the 100 rpm, I look at it this way. If I am able to get the prop in tune with the engine and I can pick up on the average a 1/2 gallon of fuel per hour for 100 hours, that comes to 50 gallons savings. At $4.70 a gallon that is a savings of $235.00 per year, or approximately 10 cases of grog.

[Serenity]

Not to beat a dead horse, (Why would anyone want to beat a dead horse is beyond me) but I have spoken to several yard owners and mechanics regarding the lubracation of the shaft. Don't do it, the prop will be a almost impossible to get off.

[jleonard]

I have lubed and not lubed. The prop comes off either way in my limited experience. I see more pluses to lubing than dry.
It is far easier for a mechanic to assemble dry. That is for sure.
I can say there were many times that I intended to use anti seize for example, but I forgot when in haste to get things together. I justified by saying that it didn,t matterI guess the horse is really dead now. Lol