Corrosion on mast fittings

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Kyle2

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I have lowered the mast this winter - the first time since I got the boat, a Snapdragon 747. The alloy casting at the top of the mast has several S.S. pins passing through it, securing the forestay and backstay, and the halyard sheaves. There is also a rusty bolt which secures the shrouds and the VHF aerial and anchor light. These all seem to be set solid in the casting, presumably by corrosion of the alloy casting. I want to remove the pins to replace the forestay & backstay, and replace the rusty bolt with stainless. I think my next step will be to drill out the three rivets holding this casting to the top of the mast, as it will be easier to work on when removed, but how can I release these seized pins and rusty bolt? Any tips gratefully received!
 
Heat is the answer. The reason being that aluminium expands more than steel or stainless steel and so releases its grip.

Boiling water, hot oil (but that's messy ) or even dry heat using a hot air gun maybe. Perhaps worth trying the hot air gun before removing the fitting especially as you'll be able to concentrate the heat on the aluminium.

let it soak for a while in plus gas by all means, it might help but you'll still most likely need the heat. Dont shear the bolts off!
 
And even with heat it might not work. I've just stripped down my furling gear and the three bolts holding the flanges to the drum were solid. I used heat - lots of it - along with a fly-press to see if the bolts would shift. Not a chance.
Drilling the bolts out is an option, but is more difficult than it sounds. You need to drill stainless with a low speed, and the drill will tend to wander into the softer aluminium. I ended up having to make a flat-bottomed milling cutter with a long shank, along with a milling machine, to get the wretched things out.
Assuming you win this fight, make sure that you etch-prime and paint all the components and use Duralac when you re-assemble.
 
My tragic experience

of trying to remove stainless/alloy corroded items is that it's only feasible in about 40% of cases.

Heat is the least unsuccessful, penetrating oil of any kind a waste of effort.

If you do have to drill out, replace the massacre you've caused with a piece of turned aluminium rod pressed into an oversize hole you've cut with a keyhole bit.

I've just been able to find 3 replacement stanchion sockets at the Barge, for £10 each, instead of £38 that the new replacements would have cost me.
 
It's worth persisting. I'vejust discovered my Snapdragon 747 mast has cracks and compression fractures between the spreader rivets and extending up to the shroud bolt. Needs a big repair or a new mast! By the way, can you measure the length of your mast? I may need a second hand one and mine is locked in Phil Evnavans' yard. Very grateful if you could tell me how tall it needs to be!
 
I haven't yet made an exact measurement, but the mast is approximately 8 metres. I'll try to make a better measurement tomorrow. I guess I may end up needing a new mast too, if the corrosion problems can't be sorted out. Thanks everyone for the help. I think I will remove the casting and try application of heat.
 
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