1956 Johnson 30HP prop nut confusion

[Jdunham]

Hi all,
I have a bit of a conundrum. I am ready to do a water test on my 1956 Johnson 30HP and have discovered that the prop nut that I ordered (and the alternate one listed in my parts manual) are both threaded nuts. The propeller shaft on my motor is not. I thought nothing of it until I went to install the nut. I have only ever worked with a few outboards, all of them old OMC units and ALL of them have had threads.

The two part numbers are:
375773
and
376731

The difference has to do with the RDE-18 and RDE-18C I thought but I still cant figure out what actually changed from one motor to the next within that 1956 year.

I do know that the lower unit on the motor was removed and put back on at some point in its life and it is conceivable that it is not the original lower unit. The lower unit is a Johnson (original red paint) but was moved to an Evinrude (based on the repaint it received) and then moved back to this motor. All of this happened before I acquired it. My question is this: How do I keep the prop on? How do I identify the correct nut for this lower unit? Is this a common means of mounting propellers?

Thanks to any who can shed some light on this.

Note: I will deal with the paint color mismatch once I know everything is mechanically sorted out

JD

 

[Chinewalker]

In the 1960s, OMC changed the propshaft from a threaded tip to a smooth tip with a slot. The propshafts are interchangeable. Guessing that at some point in the last 60+ years, your motor has had a propshaft transplant. You would need to find the correct prop nut, plastic, from the 1960s. I believe it is part number 305294.

 

[F_R]

Confirming, the slip-on nut is 305294. Be sure to use a stainless steel cotter pin 306394, a 304576 thrust washer, and the correct drive pin 304575.

 

[Jdunham]

Thanks Guys,
Whats the reason for this design? I get that in forward there is no issue but in reverse doesnt the cotter pin take the full load of the thrust. Has anyone ever complained of this shearing a cotter pin or breaking the plastic nut? The old design put the load on the threads and the cotter pin simply kept it from unscrewing.

I will get that nut on order today. The thrust washer, and cotter pins are the same part numbers that I already have.

Thanks,
JD

 

[F_R]

The prop is held in position by the drive pin, not the cotter pin. You could actually run it without the nut, if you could keep the drive pin in place. Hey, the threaded nut wasn't foolproof either. A sheared pin or spinning rubber hub would cause the prop to touch the nut and unscrew it off the shaft, especially if it had an old rusted cotter pin. That's why it is important to use the correct parts.

 

[Jdunham]

Thanks F_R, I had not thought about that possibility.

Does this mean that I also need to pick up a new prop now rather than later (mine was abused by someone but is ok for testing)? I want to stick with the original 10 3/8x12 1/2 but do not see that listed in the 60s as a size that was matched with a motor. Is the newer shaft totally backwards compatable with the older props?

I am going to be pushing a heavy boat. Its an 18' cedar strip w/o fiberglass so will soak up water. I did not want to move up to a steeper pitch that was listed for the 33hp model.

JD

 

[Chinewalker]

The props are completely interchangeable. Get something close in diameter and pitch and you should be good. You may actually want to go down a hair in pitch as you've got a sizable boat there. Your motor will be happiest peaking around 4500 RPM. Borrowing a shop tach may help in your selection. Has this motor been used on this boat before with that prop?

There are used props all over eBay you can get cheaply to try out, and having some spares is never a bad thing.

 

[Jdunham]

Thanks Chinewalker,

No, I picked this motor up 2 summers ago and the boat was not seaworthy at the time. The 2 will meet for the first time this summer. Thanks for the RPM suggestion. Is there a good guide for choosing props? I understand that a smaller pitch will keep the RPMs up on a bigger boat but I also don't want to spring for 4 or 5 different props before finding the best one. If I do some testing with the 10 3/8 x 12 1/2 that I have and get a WOT RPM reading, can I use that relationship to work backwards to select my new prop?

If I understand the rules correctly, the risk to the engine occurs from overspeed not underspeed right? So I would want to make sure I limited my WOT RPM with the boat at its lightest (just me) rather than when it is loaded with up to 6 people? I had thought that they want to keep that motor under 5k rpm as a top limit. that may be different from the optimum operating rpm that you are referring to.

I have another thread here discussing tachs for these old 2 strokes. I am still designing my dash set and had wanted to run speed, temp, tach and a few other things Finding retro looking gauges isnt cheap. That whole thing may not pan out but I did read about the tinytach system which I will pick up for these tests.

As for the ebay props. I was not sure about compatability over the years so was restricting my searches to ones I knew would fit the early 60s motors. I opened that up a bit and you are correct, there are lots.

I totally agree on the spare props. That boat lives on georgian bay in ontario where there is no mud or sand...just rocks. We ALWAYS carry spare pins and prop nuts and, on long trips, an actual spare prop. (the rest of the time you just row back). Whoever hits a rock buys the new prop so folks learn pretty quick to play it safe.

 

[jimmbo]

A heavy 18 ft boat is probably going to need a something like an 11 inch or even a 10 in pitch.

There are risks to the engine on both over revving or overloading. Over revving means higher pistons speeds which means more stress on crankshaft, connecting rods, piston pins, pistons and rings. Overloading leads to higher piston crown temps, carbon buildup behind the rings, leading to stuck and broken rings, and cylinder scuffing and scoring. Even though the WOT range is listed as 4000 - 5000 rpm, it is preferred to prop so it is in the 4500 - 5000 range.

Use a TCW-3 oil mixed at 24:1. If it hasn't been done, you might want to consider converting the engine to a fuel pump system and ditching the pressurized fuel tank.

 

[oldboat1]

Jimmbo is undoubtedly a fine family man -- kind to kids and pets, and a good neighbor. But he's wrong about the pressure tank for your '56. It's a good system, and I would stick with it for a resto. project.

Weren't you working on a Duratech hull (barn find, I think, or maybe one that was in the family)? What's the 18' cedarstrip? sure would like a pic or two of that one -- big boat compared to the Duratech. Soaking to seal joints isn't the same as water logging, and I don't think the added weight is much of an issue. But overall size of the 18 footer might be an issue if it's a beefy model.

Interesting stuff. I think I would stick with the stock prop and see what performance you get out of it. Chances are the issue will be the 30 ponies, not propping -- but won't know until you try. (Part of the fun.)

I see twin 30s....

 

[jimmbo]

My dad and uncle both had 57 and 55 Big Twins and the pressure system never stranded us. I suggested ditching the Pressure System, simply because of the lack of range the 5 gal tank has, and having to refill aboard. Plus it is next to, if not impossible to get larger pressure tanks.

 

[82rude]

What kind of cedarstrip do you have? I had the giesler 17 foot and weight was 550lbs .Mine had a 90 evinrude and was classed as homemade and rated for 90 .It .,would also be equally happy with a 30 to 60 I would highly recommend glassing the bottom.If there was any water in my boat it was spilt there.If your ever up around sault ste marie pm me i have a mechanically adjustable prop for a 56 and pressure tanks that i could be talked into loaning on a permanent basis.

 

[Jdunham]

Thanks guys,

To answer a few questions. We are going to keep the pressure tank. I have scrounged up 3 of them (2 good, one with a peculiar puncture in the bottom that I will braze). New double fuel line is available and the connectors can be easily rebuilt when needed. The concerns about on board refilling are legitimate, but when I put new lines on I used 10' per tank so I can just lift it right out onto the dock.

The boat is an 18ft Giesler, Nippissing model. For the last 15 or so years we have been rebuilding it in the 2 week stretch we have at our camp each season. Last fall we made the sad decision to declare defeat and purchase a new boat built to matching specs so that we can use it before we become old and feeble.

The camp we keep the boat at is more or less unchanged in the last 70 years so the pressure tank, old motors and cedar strip boat fit the scene.

The 30HP is considered fine for that boat, maybe not the fastest, but the easiest way to damage one of those gieslers is to pound it through the waves to hard and crack ribs at the sharpest bend near the stern. A motor on the low end of the power range will help prevent this.

I am not really doing a restoration on the motor(s) ( I have 2 but only 1 will be running this season) More of a quick refurbishment and then a season of testing. If everything runs well I am going to clean and paint the exterior to match and may buy a new decal set. Both of these we beat around by previous owners and are a long way from pristine. The second motor is technically a javelin but is missing almost all of its chrome. The one piece still there is mangled and corroded.

We went back and forth on the fiberglass option. While it does keep the water out, it also keeps it in. This boat sees use for 3-4 weeks per season. The soak time is between 2 and 4 days and it can be used in that time anyway. With fiberglass we would need a canopy and would need to be quick about pumping out splashes or rain. At the end of the season any moisture in the planks will stay there much longer and will eventually lead to earlier rot. The fiberglass is also heavier. This boat is stored in a boathouse in the spring, fall and winter. If at some point we wish to glass it, it can be done later.

As for the Duratech, yes, thats me. I still have it, I still want to fix it. I want to put the second 30 on it eventually (the other reason not to run 2 on the giesler) but I have had to make some prioritizing decisions and that boat lost. I did remove the bad patch so while it is still stored outside there is no risk of further damage (cant hold water anymore, there is a 6"x60" hole down the middle of the hull) I realized there was more work needed than repatching so I stopped before I got too far in. Most of the rivets below the waterline are severely deteriorated to the point that the heads on the outside really arent there. I need to re-rivet most of the hull before I risk putting any power to it. Yet another good excuse to buy a tool (pneumatic chisel with rivet driver)

82rude, I will certainly keep that in mind. I actually dont know what an adjustable prop looks like but at a guess it would let you tune it in until it was just right for the load on the motor and then you could purchase a fixed one matching that spec? I do need to pick up a 4th tank at some point because I have a second boat/motor that runs the pressure tank system. This one is a 1965 powassun giesler with a 1955 Evinrude fastwin 15 on it. I will see if I can make the image upload.

 

[racerone]

Where in Georgian Bay ?------Parry Sound area ?

 

[82rude]

Mine was a modified kipawa.Also had the same 14 footer as you as do several camp operators up north.You bought a new giesler ?Nice .Hers my old beast ,i sold it as it wasnt right for my needs anymore as i fish up in rough country a lot now so i got a old starcraft ss160 .