Did I break my prop shaft? - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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Old 07-12-2009
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Did I break my prop shaft?

I've got a Vetus m3.10 diesel. I was motoring a couple days ago and all of a sudden I lost what felt like 90% of thrust to the prop. Engine was running fine, at minimum throttle in gear the boat would slowly move at what felt almost normal, but any increase in throttle would result in no increase in speed, and a metal-on-metal squeal.

Thinking I got something caught in the prop I dove under and there was nothing.( I did notice however that the new zinc on the shaft behind the prop had fallen off? -might be related).

We sailed back into the harbor and was able to slowly motor to the mooring at minimum throttle.

I checked the transmission fluid, level good and clean. I just changed the transmission fluid this spring, less than 10 hours of motoring.

We were able to reproduce the metal-to-metal squeal with me under the boat, with the gear engaged and giving the prop a turn, the shaft will spin, but the coupling does not.

Back in the boat, engine running, engaging the transmission in reverse the shaft was able to be pulled back about 3/4 of an inch from the coupling, putting it in forward the shaft is driven back into the coupling.

Looking at the Vetus diagram for this coupling, it appears that there is no key? But a pin driven through the coupling and shaft. see below:

My plan is to take apart the two halves of the coupling to see what's going on inside. Did I break the shaft, or the pin that goes through the shaft? Is there a through-pin? I'm hoping that the front part of the coupling does not need to be removed as I don't have a spanner type tool that will fit that, and it looks like with a 130 lbs it could be a bear to remove.

Anyone have any other ideas or suggestions? Things to look out for? Don't assume I know anything about couplings, yesterday was the first day I've even given this thing a good look.

PS. For those who know the main coast, we were motoring around the west side of Seguin with a west wind making it an imposing looking lee shore. I was saying "this would be bad spot for engine trouble"..shortly after which we rounded the southern tip of the island and the above engine issue happened. We were able to easily pull up sail and tack away from the island, but if had happened 15 minutes earlier we'd have been in for a fight!
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Old 07-12-2009
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Quote:
Originally Posted by preservedkillick View Post
...........Did I break the shaft, or the pin that goes through the shaft?..........
You just couldn't have broken the shaft!....Could you? The torque required to break a shaft would have been felt.

I'm betting that you find a sheared pin when you take your coupling apart. The squealing occurred when there was enough torque applied to the shaft to make the propeller turn slower that the coupling. In other words, it couldn't keep up because of the resistance of the propeller.
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Quote:
Originally Posted by Selkirk View Post
You just couldn't have broken the shaft!....Could you? The torque required to break a shaft would have been felt.

I'm betting that you find a sheared pin when you take your coupling apart. The squealing occurred when there was enough torque applied to the shaft to make the propeller turn slower that the coupling. In other words, it couldn't keep up because of the resistance of the propeller.
I sure hope not. We were motoring easy, about 4 knots, pulling a dingy, not much for waves. Don't think we hit anything or got cought up with anything, we just lost power.

How often do these pins shear? is there standard sizes standard to buy new ones? My shaft is bronze (possibly old) and when the new engine was put in they used a stainless pin..corrosion? I just hope I can get that coupling apart to see. I also expect that driving a broken pin out could be a difficult. Although, a broken pin is better than a broken shaft.
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I agree with Selkirk, most likely you broke the Shear Pin.

You can test this with the Engine OFF. Put the Engine in gear and with a Pipe Wrench (or Vice Grips) try to turn the shaft on the other side of the Coupling.

You will need to remove the spanner nut if it turns out the pin is broken. (This can be done with a hammer and a flat head screwdriver if there is room.
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Quote:
Originally Posted by bheintz View Post

You can test this with the Engine OFF. Put the Engine in gear and with a Pipe Wrench (or Vice Grips) try to turn the shaft on the other side of the Coupling.

You will need to remove the spanner nut if it turns out the pin is broken. (This can be done with a hammer and a flat head screwdriver if there is room.
This is about what we did. Engine in gear, I was able to tun the shaft by turning the prop while under water. The shaft turned but the coupling did not. Where does one by these shear pins? Standard items? I'd like to go back to the boat with all the parts so I can repair this in one trip.
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Quote:
Originally Posted by preservedkillick View Post
.............How often do these pins shear? is there standard sizes standard to buy new ones? My shaft is bronze (possibly old) and when the new engine was put in they used a stainless pin..corrosion? I just hope I can get that coupling apart to see. I also expect that driving a broken pin out could be a difficult. Although, a broken pin is better than a broken shaft.
I don't think the shear pins break all that often......don't really know, but I'm betting that yours just corroded into two pieces.
If you can get to it - and you can, it's just a matter of how - it will come right out if you use the right size drift pin. If you don't know, a drift pin is sort of like a center punch except that it is not tapered and comes in several sizes. Do yourself a favor and drop in a Sears and buy a set of five or six different sizes.

And watch what you use for a shear pin. If you find your shear pin is all corroded, then someone found a material that should never have been used. I'd have to study up myself before I selected the right material, so I really can't offer advice there, but you'll know what size shear pin to get by what size drift pin fits into the hole.

BOL!
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Old 07-13-2009
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D=Diameter of prop shaft in MM
A=Diameter of pin and drill bit to drill outin MM
B=diameter of drift pin to use in MM
Just measure the diameter of the prop shaft and you are home free.
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Some things to remember when trying to remove the old pin.

Since the shaft has spun in the flange the holes will most not be aligned so that just drilling straight through will not be an option.

You might get lucky and find some kind of alignment marks that will clock the flange to the shaft and maybe try just knocking the pin through in three pieces.

You may have to slide the spider off and remove the broken pin that way.

Looking at the digram closer it looks like there is a key at the 6 O'clock position on the spider and 12 O'clock on the drive flange.
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Last edited by timebandit; 07-13-2009 at 06:08 PM.
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AND---

It looks like they want you to torque the collar nut to 210 foot pounds so you had better get a wrench and a pipe.
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Old 07-15-2009
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Well, came apart easy. No shear pin. There's a set screw where the diagram says the pin should be. And the collar that requires the 130 lbs was very loose. Light tap with a hammer & screwdriver and it ws free. I've got a proper hook spanner wrench on order.

Thanks guys.
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