Johnson 4R72S whoops!

[Grem]

Since getting my motor working, I've used it for several hours on the lake and both the running and starting have improved significantly. That's probably in part due to getting used to how it likes to be treated............however this afternoon I hit a snag. Well, a submerged tree to be precise.
It didn't stop running, but the drive to the prop failed and the prop now spins freely.

What have I likely done and what should I do next?

 

[freddyray21]

Re: Johnson 4R72S whoops!

either sheared a pin or spun a hub

 

[Rick.]

Re: Johnson 4R72S whoops!

Glad your getting some fun out of it. You have probably broken the shear pin. You need to pull the prop and you will see the pin in the white plastic ring the prop fits over. You will need to get the pin before hand. Get some extra. Rick.

 

[Grem]

Re: Johnson 4R72S whoops!

^^^^^

Thanks for the quick reply guys.

Yes, we've had a huge amount of unexpected fun with it (mid 70s since the weekend in central 'bama) and I was hoping for a couple more outings before I go back to London in a couple of weeks.

So to remove the prop, I take out the split pin and just undo the large nut? Is it a loose fit or will it need levering off?

What does 'spun a hub' mean and is that serious?

 

[Rick.]

Re: Johnson 4R72S whoops!

You never know how it's going to come off but you have to get it off. I took mine off last night and I had to pry it off carefully with a couple of large screw drivers. Once I replaced the shear pin, the prop slid back on with no problem. You grease the steel shaft only, not the prop rubber. Turn the nut in by hand until it is tight and then turn it in until the hole for the cotter pin lines up. "Spun a hub" may have happened but probably not. The term refers to the rubber that is pressed into the prop losing it's contact with the prop and breaking free causing the prop to spin independent of the rubber. If that happens you have to replace the prop or have it repaired by a prop shop. It was the first time I had mine off and the manual simply says "remove the prop" so I expect they figure we should know how already. I didn't expect ti to be so tight coming off but once you see how it is put together you will understand that the prop can really tighten onto the nylon bushing if it has made contact with an object. Have fun. Rick.

 

[Grem]

Re: Johnson 4R72S whoops!

Thanks Rick.

The prop came off very easily after all and sure enough the shear pin was toast.

I called a couple of places here in central Alabama but neither have it in stock.

Are these pins model specific or generic across many applications?

I was hoping to pick some up rather than mail order as I only have a couple more opportunities to use the boat until the Spring.

 

[Bear 45/70]

Re: Johnson 4R72S whoops!

Usually model specific.

 

[Grem]

Re: Johnson 4R72S whoops!

^^^^

Ah, thanks. Guess I'll have to go with mail order then.

 

[fix_it]

Re: Johnson 4R72S whoops!

Until you can get the propper pin, I would think that a piece of brass rod of the right diameter could be used. It would surely be softer than the steel pin and therefore may break more easily, but would not otherwise cause any harm. That could get you back on the water at least. Just don't use a bolt or nail or.... Lower unit gears aren't cheap.

 

[Grem]

Re: Johnson 4R72S whoops!

Until you can get the propper pin, I would think that a piece of brass rod of the right diameter could be used. It would surely be softer than the steel pin and therefore may break more easily, but would not otherwise cause any harm. That could get you back on the water at least. Just don't use a bolt or nail or.... Lower unit gears aren't cheap.

Yes, when I retrieved the broken pieces I assumed the pin was bronze, seeing as how cleanly it sheared. The bad news is that I don't have any workshop facilities while I'm staying with my g/f and so finding/adapting any stand-ins would be near impossible.
The good news however is that after a lot of phoning around (and discovering these things appear to be like hens' teeth) I located some in CT this morning and the guy was very helpful and promised to have them in first class mail today. (Mc Carthy Marine, FWIW). I'm hoping to be back in business early next week.

 

[Bear 45/70]

Re: Johnson 4R72S whoops!

Hardware store will have brass or bronze rods. Buy rod of correct diameter and cut to length. Carry spare shear pins and cotter pins if used, inside motor cowel of taped to tiller handle.

 

[Grem]

Re: Johnson 4R72S whoops!

Hardware store will have brass or bronze rods. Buy rod of correct diameter and cut to length. Carry spare shear pins and cotter pins if used, inside motor cowel of taped to tiller handle.

Thanks for the tip! I've ordered two from the store. In reading other comments I realise that since my prop (original '72 I guess) doesn't have a rubber bush inside, this could be a regular occurrence in our tree strewn lake.
I will take the spare back to London with me and make up a bunch of replacements to match. How critical is the choice of material? Is there a particular no-no? I just checked a piece of the original and although it's black and un-corroded, it's magnetic.

I'm going to bring back a little tool kit to keep with the boat too.

 

[F_R]

Re: Johnson 4R72S whoops!

I believe that if you look closer you will find that it indeed does have a rubber ring between the propeller and hub. Because the rubber absorbs impact and protects the drive parts, the drive pin is supposed to be stainless steel. It is a "drive" pin and not a "shear" pin and won't be breaking so easily if you are using the right one.

 

[Bear 45/70]

Re: Johnson 4R72S whoops!

F R is right almost all props have a rubber hub. A few high performance and most racing props don't. But all props for the normal recreation do.

 

[Grem]

Re: Johnson 4R72S whoops!

Well I've had another look and there is no sign of any rubber in the prop assembly. It appears to be a bronze bush let directly into the cast ally blades. The recess for the drive/shear pin is machined into the bronze. When I removed the prop, the pin was in three pieces.

???

 

[asdasc]

Re: Johnson 4R72S whoops!

Turn the nut in by hand until it is tight and then turn it in until the hole for the cotter pin lines up.

Just curious, is this correct? I have always (which means the 2 months I have had an outboard) tightened it by hand, and then back it off until the holes aligned for the pin. I haven't tried to tighten it further. It doesn't have to be real tight to work does it?

 

[Bear 45/70]

Re: Johnson 4R72S whoops!

Well I've had another look and there is no sign of any rubber in the prop assembly. It appears to be a bronze bush let directly into the cast ally blades. The recess for the drive/shear pin is machined into the bronze. When I removed the prop, the pin was in three pieces.

???

The rubber is between the bronze and the aluminum. You can't see it if it is normal. If you see it it means the rubber slipped and you now have a "spun hub". A lot more expensive to fix than a shear pin or drive pin if you prefer.

 

[Bear 45/70]

Re: Johnson 4R72S whoops!

Just curious, is this correct? I have always (which means the 2 months I have had an outboard) tightened it by hand, and then back it off until the holes aligned for the pin. I haven't tried to tighten it further. It doesn't have to be real tight to work does it?

You should be able to slide the prop onto the shaft by hand. Insert pin and install nut, finger tight if the cotter pin lines up and you are good to go. Wrench tightening justs puts more stress on the pin.

 

[F_R]

Re: Johnson 4R72S whoops!

Well I've had another look and there is no sign of any rubber in the prop assembly. It appears to be a bronze bush let directly into the cast ally blades. The recess for the drive/shear pin is machined into the bronze. When I removed the prop, the pin was in three pieces.

???

The picture I posted is typical of the 3 and 4 horsepower propellers for well over 20 years. At some point (after yours) they quit using a nut to hold it on but the hub remainded the same. The rubber ring is splined to match grooves in both the prop and hub. If you cannot believe this, then go ahead and use brass shear pins and put up with changing them every time you touch a submerged object. But for me, I will go with the way the engineers designed the motor.

 

[Grem]

Re: Johnson 4R72S whoops!

^^^^^^^^^

Ah, I see now. The hub was stuck into the prop and once I saw the diagram all is clear - Thanks!

As I said, I have a bunch of different pieces of stock rod in London, so I'll try to match up with the o/e pin. I wonder if softer pins would be a good idea since I know the lake has lots of submerged branches?