Shear pin - Brass or Bronze

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tim_ber

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I want to turn a few shear pins (yep, broke one today and couldn't find my spare in the tool box - was I annoyed or what)

Anyone know what they are made of?

For a 2 stroke 2.5hp Mariner engine.

Thanks in advance.
(I have googled - no luck)
 
Interesting.

Is your prop plastic? Mine is.

All the ones I've ever had are a brass colour.

I'm thinking it will be made of brass, shears a bit easier than bronze which may be more brittle, but too hard in the long run.

I ended up cutting a steel pin off a bit of the rowlocks and using it as a shear pin and limped back.

Felt really stupid for not having a spare. All my other outboards have two in little rubber holders under the cowling.
 
tim_ber said:
Interesting.

Is your prop plastic? Mine is.

All the ones I've ever had are a brass colour.

I'm thinking it will be made of brass, shears a bit easier than bronze which may be more brittle, but too hard in the long run.

I ended up cutting a steel pin off a bit of the rowlocks and using it as a shear pin and limped back.

Felt really stupid for not having a spare. All my other outboards have two in little rubber holders under the cowling.
Click to expand...
On a 2B - s/s
There's also a little rubbery-plastic holder on the tiller which holds 2x shear pins and 2x split pins.

Can't imagine a shear-pin being made of brass - as it would rot (de-zinc) in seawater, then become as soft as 'you-know-what'.
 
Thanks.

My shear pin must have been bronze then.

I've never seen bronze coloured s/s and the broken bits were soft, bronze colour. (This was the shear pin supplied with engine)

I've got bronze, so I can use the lathe to turn a few out. I have got a few s/s bolts I could turn down, but bronze should be ok shouldn't it? I mean proper boats have bronze props don't they?
 
Ive been making mine out of brass for years cos thats what was in my engine when I got it. This is for a 4hp Yamaha 2stroke.
I may just try turning stainless ones for it instead. Theres no chance of my prop ever touching the bottom in anger!
 
This may be perpetuating an urban myth, but I was given to understand that the plastic props use a brass pin, whilst the metal prop uses a stainless pin (Tohatsu and thier Mariner badges versions). I would guess that a brass pin would last several years before rotting away...

Rob.
 
My elderly Mercury 2.2 has a plastic prop and a brass pin.
My feeling is that bronze might be too tough for plastic, esp if it's drawn ph-bronze rod, which much small dia. stuff is likely to be. SS would be even tougher.
 
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Maybe a correction is in order ... mine LOOK like s/s - of course, they could be plated brass for all I know.

If I was going to make my own from s/s, I wouldn't turn down a bolt - but either cut lengths off a s/s welding rod, or use a suitable s/s split pin: they're soft enough. (with a dab of Araldite holding the two halves together)
But - for the small money involved, I'd be happy just to buy 'em.
 
It is very difficult to differentiate between the various copper alloys without sophisticated equipment. One way that might work for you is reference to this website http://www.metalreference.com/Forms_Copper_Alloy.html Note that phosphor bronze is a tin bronze with a very small phosphorus content for deoxidation purposes. All the tin based alloys have a rather pink appearance by comparison with zinc-based ones.
 
Thanks for all the information, this was an eye-opener.

I'm going to use brass then.

I imagine the original pin did as Electrosys suggested - became too soft.

I think the pin gave way under full load and prop did not touch seabed.

If I make a load up and glue them all over the engine, then even if the one being used 'rots' at least I have a load of nice new soft ones to replace it.
 
tim_ber said:
I imagine the original pin did as Electrosys suggested - became too soft.
Click to expand...

Dezincification of brass takes about five years in skin fittings. This is supposedly the expected life of the rubbish that is being sold for the purpose these days. In a small shear pin I assume the process might take less due to the smaller surface area but I wouldn't think it would occur in less than a year of constant immersion.

You can see the problem in a propeller nut that was about 16 years old here. This is possibly a modified brass (manganese bronze) although I'm not certain.
 
Our Mariner 2.2 had a 'brass' pin (plastic prop). B&Q used to sell lengths of brass rod that were the exact diameter for a few £. (One length would make a lifetime's supply of shear pins.)

Andy
 
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