Using a nail as an outboard shear pin?

Tim Good

Tim Good

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I sheared my shear pin the other day on a Mercury 3.5 when my painter line fell in.

I went to an outboard workshop and they didn't have any but gave me a nail of the same diameter and said it would be fine. I asked it it would be too strong and not shear as easily as the genuine part. They said it would be fine.

I'm unsure what material the nail is but just want to get a second opinion on this?
 
I rented a cottage on a remote Scottish island called Eilean Shona about 20 years ago. There was a small boat available and we went for a trip to a local beach. The onboard prop started free spinning on the shaft and on investigation there was no shear pin. I botched up a make do from the wire handle of a bucket on the boat bending it repeatedly to cut it and knocking it flat with a stone. Worked fine for the week we were there. I think your nail will be ok.
 
The short answer is "Don't!"

The long answer is "If you are after a cheap source of suitable shear-pins just pick up a vernier calipers (or borrow) and go to a shop that sells knitting supplies. Pick a pair of the size that has the correct diameter (that why you will need the calipers) and hand over your money. Cut the needles into the lengths that suits the prop / the slot in the prop hub and after a few minutes with a junior hacksaw you'll have a ready supply of spare shear pins for than less what you'll pay for the 'proper' thing. Yes, the 'proper' pin would probably be made out of sintered bronze (often just brass wire) and yours would be made of aluminium but so what? Under normal use they wouldn't break but will only do so when the prop is snagged. This is what I did when I had no spares.

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northcave said:
I sheared my shear pin the other day on a Mercury 3.5 when my painter line fell in.

I went to an outboard workshop and they didn't have any but gave me a nail of the same diameter and said it would be fine. I asked it it would be too strong and not shear as easily as the genuine part. They said it would be fine.

I'm unsure what material the nail is but just want to get a second opinion on this?
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I would have thought that it would drive the prop just fine but would not shear if required to, so fine as a temporary repair to get you home or going again until you can get a proper one.
 
Try Ron Hale Marine,

Portsmouth

for proper shear pins ( and get a few spares + spark plugs &the usual minor toolkit if not already ).

- they do all this sort of thing and all sorts of bits and add-ons inc 12v charging coil kits for maybe slightly larger ( say 4hp up Yamaha etc motors ) well worth a call, they do mail order all the time.

http://www.ronhalemarine.co.uk/
 
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Many years ago I went gliding with a a winch launch. Shear pins cost money and so to save a little a wire nail with the same strength was substituted. This was fine in theory but the quality control of nails is not consistent and every now and then we had a soft nail, the strop would part and the launch was aborted at some random moment of take off. The harder you tried to get lift the greater the strain on the wire and the more likely the failure to occur. Interesting landings.

The choice is yours, it will probably be OK just be aware it might not sheer when needed or it might sheer early.
 
Different metal and shear loads too; try banging in a hinge or something with a prop' shear pin - still if eveyeryone's happy, go for it I suppose - in WWII fine - I'd said give it a go with a cropped nail etc, later if paying for rides maybe not so much,,,:)
 
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I used to run my 3.5 Merc in the marshes a lot, which led to shearing pins. The Merc price is crazy high, and one day I just needed something, so I went to the corner hardware, got a 2' length of brass rod the same diameter, and with a hacksaw and bench grinder had a lifetime supply of proper pins in about 10 minutes.

Strange thing was, At about the same time I stopped visiting the problem area and never sheared another pin.

But no, I would not use a nail other than to get back to the boat. That's what the oars are for.
 
lukedh said:
Many years ago I went gliding with a a winch launch. Shear pins cost money and so to save a little a wire nail with the same strength was substituted. This was fine in theory but the quality control of nails is not consistent and every now and then we had a soft nail, the strop would part and the launch was aborted at some random moment of take off. The harder you tried to get lift the greater the strain on the wire and the more likely the failure to occur. Interesting landings.

The choice is yours, it will probably be OK just be aware it might not sheer when needed or it might sheer early.
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With aircraft re release speed and height - unexpected - that is madness.
 
Just to clarify

The shear pin is used as the weakest part of the power train that will fail if the prop hits something

If you use a nail and hit something and there is something weaker than the nail in the power train it might fail instead of shearing the shear pin

The nail would be a get you home measure but i would replace it with a correct shear pin as soon as possible to protect the rest of the power train from damage

Regards Don
 
Sounds like a pointless risk given costs of repairs if it didn't break as required however if your split pin broke and you had a spare nail on you to cross a known stretch of water I would probably be tempted for aone off solution to get me home but not further however I try to keep a spare split pin with the engine to avoid the temptation to use nails or knitting needles etc. Ultimately it's all down to your level of desperation to motor off and if you carry any nails maybe?
 
Consequence of using a steel shear pin might be losing propellor blades.
Buy a foot length of brass rod on ebay.
 
lw395 said:
Consequence of using a steel shear pin might be losing propellor blades.
Buy a foot length of brass rod on ebay.
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Ive never come across brass shear pins. I would use one as a temp measure but replace as soon as poss. My Hondas hAve a couple of spares stored under the lid and the Seagull uses a spring.
 
ashtead said:
Sounds like a pointless risk given costs of repairs if it didn't break as required however if your split pin broke and you had a spare nail on you to cross a known stretch of water I would probably be tempted for aone off solution to get me home but not further however I try to keep a spare split pin with the engine to avoid the temptation to use nails or knitting needles etc. Ultimately it's all down to your level of desperation to motor off and if you carry any nails maybe?
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Most OBs have a separate shear pin inside, the split pin only keeps the prop on.
You may find yourself equally taken short if you only carry a split pin!!
 
Bought a couple of new shear pins for my Mercury 3.3 last week as the original brass one had sheared, and the new ones came in stainless steel: marked Mercury on the packet. I asked the dealer why and he said ".... they've changed - the old brass ones broke too easily".

On the little Tohatsu/Mercury/Mariner engines the visible split pin is not a shear pin - the actual shear pin is hidden inside the prop hub. Confused me at first....
 
Seajet said:
With aircraft re release speed and height - unexpected - that is madness.
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All glider pilots are trained to handle cable breaks at any point in the launch. The vital thing is to lower the nose to get flying speed, and then you can decide if there is space to land ahead or if you need to circle to land. Nothing particularly difficult about it: huge fun.
 
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