Lower mast halyard sheaves - freeing up

[Guest]

Take an average style mast with internal halyards. The halyards enter mast at bottom foot via sheaves on pins through base..... up to similar sheaves at mast-head.

Masthead sheaves are fine .... but bottom sheaves are seized. You have small plates and self-tapper screws holding the sheave pin in place. The sheaves are literally caked around with white / green salts .... one in fact is just solid.

Now the question is ......... has anyone managed to free similar without unstepping the mast ? I've tried removing the small end plates and extract the sheave pin - but solid - won't budge. The mast design is such that the sheaves can be taken out while mast stepped .... IF I can break that solid mass of salts etc. !!

Here is a piccie of the mast base ......

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[nordic_ranger]

Try puting the offending part in boiling water for a while, this might disolve the salts.

 

[stephenh]

white vinegar is very good for this....

 

[Guest]

Boiling water .... trouble is I don't want to unstep the mast again ..... and is difficult to maintain hot water round it without.

Vinegar or Kettle descaler was a thought I had ... along with "shock" to try and break the bond of the salts to the sides / sheaves etc.

 

[Lakesailor]

We used to pour boiling water from a kettle onto salty type corrosion on car batteries and it worked a treat.

Though I'm sure it's not the same thing at all.

 

[rogerthebodger]

I had the same problem at the top of my mast and I found it was a stainless pin in aluminium mast and the white stuf was corrosion which ment using heat , a big hammer and a big wrench to get it out.

In your case at the bottom of the mast you can get to it. If the sheaves are in a sheave box I would remove the box and sheave from the mast and you can then try various means on the bench. The best pressure to apply is with a press so if you canot remove the sheave box from the mast try a big G clamp which may break the corrosion jam.

I have not found any common chemical to frmove the alunimum oxide but have considered the chemicals used in aluminium anadizing may work but have not tried it.

Let us know your final solution as this seems to be a reocurring problem in different ways with stainless steel fittings corroded into aluminium masts

 

[ruvane]

I have exactly the same problem.

The sides of my halyard block have swollen so badly that I can't get the block out of the mast at all after removing the screws. I could do it by widening the cutout in the mast, but I doubt this will do the structural integrity of the mast any good.

I'm still waiting for a smart solution!

 

[Lakesailor]

Correct me if I'm wrong but it looks like the sheaves are mounted in the base casting, not in seperate boxes in the mast?

 

[Guest]

The sheaves are set into the mast base with pins as axles from the side. You can't drive the pins out as the centre of the base has the slot for the deck pivot blade.

Correct the sheaves are not actually in the mast istelf ... they are in the shoe. The metals are dissimilar .... pin is stainless, shoe is an alloy cast.

 

[cliff]

Had same problem last year and managed to free off the sheaves without removing the mast or the pin.

In my case I took a hacksaw blade and carefully worked it down the side of the sheave scraping out the gunge / salt / corrosion product as far as I could (boiling water from a kettle helped greatly) then sprayed in plus-gas freeing oil and repeated every ½ hour or so. To rotate the sheave I threaded a piece of 4mm braided nylon cord round the sheave, in the top and completely around the sheave and out the bottom then in the top again and out the bottom. Then attached a couple of "toggles" to the ends of the cord and tried to turn the sheave back and forth. Eventually with a bit more plus-gas and sweat the sheaves would move a bit then it was a case of more freeing oil and working the sheave back and forth until it was turning 360°. This was followed by much spinning of the sheave and lots of wd40 to wash out the crud.

Once the sheaves moved even a little it did not take long to get them completely free just by turning them back and forth and squirting in more plus-gas or wd40.

The tricks are patience, being able to get some torque on the sheave with out damaging it and lots of freeing oil.

Next time the mast is off I intend to drill out the center of the pins and fit a grease nipple so I can pump grease up the center of the pin and out below each sheave. Should only need a squirt of silicon grease every season to keep them free /forums/images/graemlins/grin.gif
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[Guest]

So it can be done ...... good

Unfortunately when the mast was down - I had so little time and what I did try .... failed. I have soaked it in freeing oil when I left .... so I'm hoping that when I get back to UK - I can carry on and do as you describe Cliff.

It's obvious that being at bottom like that - they suffer all the salt spray and crud ..... basically over time locking up.

Cheers ...

 

[TigaWave]

I've found this stuff very effective.
http://www.worldwideaviation.co.uk/Marine/Marine%20Main.htm
I've used it on siezed up alloy/alloy alloy/stainless tufnol/stainless.

 

[Ruffles]

Spirit vinegar will dissolve aluminium oxide. Adding washing up liquid will help it to penetrate. Heat will also speed up the reaction but I suspect the will dissipate too quickly in this case.

Don't forget to hose the excess vinegar away when you have finished - it's amazingly corrosive...

BTW does anyone know of a less permanent way of insulating aluminium from stainless steel than duralac? I need to bolt a new cleat on the mast for some lazy jacks. If I tap and screw it on and put duralac in the hole I suspect I'll never get it off again.

 

[Guest]

Insulating fitting ...

Why not use GFN cleats ... the black "plastic" type .... and rawlpugs into suitable holes in mast ? That way - the stainless screws are not actually direct contact with mast alloy - plus cleat is inert material ????????

 

[PuffTheMagicDragon]

If you can get a (very) high pressure washer, it is possible to blast away most of the dirt from between the sheave and its housing, then continue, as Cliff has suggested, with a hacksaw blade.

If you can pass a string between the sheave and the block at the top and then out through the bottom - all the time staying between the sheave and the block, even if only a couple of millimetres deep - you can abrade the muck away by using what we call 'Mitchell Cord'. This is a string that is coated with abrasive and is used, see-saw fashion, by tugging alternately on the ends. It comes in various sizes, both diameter and grit.

 

[rogerthebodger]

In the past there has been much said for and against using heli coils. Where fittings are bolted to the mast for my new yacht I inteng to use stainless heli coils and then screw stainless set screws into the heli coil. If the origional thread fitting is strong enough the heli coil will be. The aluminium will corrode and fix the heli coil to the mast but the stainless heli coil / set screw interface will not (I hope)

I also am thinking of putting the sheave pins into a stainless ring pressed into the aluminium mast to try to avoid the current problem that nigel has

I have used duralac before and had very little problem in removing the screws later but I have not used it over a long term.

BTW I purchased duralac from the manufactuer in Birmingham last time I was in the UK and foumd it very very much cheper than in the normal suppliers

 

[Lakesailor]

Is there an opening here for a 21st century solution using non-metalic materials? Would carbon fibre rod be suitable for the pin? Is there a modern synthetic material with a high shear value which would be suitable?

 

[Guest]

Blasting dirt ....

This unfortunately is absolutely rock solid stuff .... so Cliffs method is going to have be from start right through.

Once cleared - I agree that washing out is good idea ....