Mast Base sheave problem ...

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

Guest
The sheaves in the mast base are solid with built up salt / deposits and have refused to yield to liquid attacks ... acid, oil, etc. etc.

Image004.jpg


One sheave has in fact over years caused mount face to distort with the pressure build-up.

Image005.jpg


Now if the small plates are removed from sides --- does that allow the sheave "axles" to be driven out ? Has anyone ever driven out the "axles" and replaced with nut and bolt to make the job easier next time ...... ??

My worry at moment I have to admit - is that trying to drive these out may crack or damage the base mount casting.

Advice / suggestions / ideas ..... all welcome !!
 
It looks as if you have already removed them from the boat. Are they really worth saving? The sheaves look pretty corroded. If you really cannot just replace the whole thing then you will have to try and drive out the central pin.
How are they fitted to the mast base? If bolted, why not replace them with the modern system of a studs fitted in to the base, with holes through them to take blocks, with stand up springs?
 
Use a vice or hydralic press ot maybe a big G-clamp to put steady pressure on the pin with a tube or socket on the other side to support the side that the pin of coming out of.
 
[ QUOTE ]
It looks as if you have already removed them from the boat. Are they really worth saving? The sheaves look pretty corroded. If you really cannot just replace the whole thing then you will have to try and drive out the central pin.
How are they fitted to the mast base? If bolted, why not replace them with the modern system of a studs fitted in to the base, with holes through them to take blocks, with stand up springs?

[/ QUOTE ]

The photos are of mast base casting ... it is still fitted to mast. As far as I remember there are substantial countersunk machine screws holding this into the mast base. I would never try to remove those as I would expect it to then create a major repair job. I have no access to marine workshops that work on this sort of thing - I'm not in Solent etc.

The sheaves look worse than they really are ... they can be cleaned up easy and its basically surface stuff. The problem is to get them out and clean out the years of crud build-up.

As to changing the system - Why ? The in-mast halyards exit nicely via the sheaves - matching the masthead sheaves etc. Once I get them free again ... the whole system will be tickety-boo ! The strange thing is that only 2 sheaves (genny and spinny halyards) out of the 4 are actually a problem. The others are nice and free. I know why ... the genny is on furling gear - so halyard is only used once a year ! The spinny one is unused basically for donkeys years ... As the Mainsail one is used everytime boat goes out - it has stayed free ... Other 4th is unused and I am contemplating swapping to it for genny if I can't get usual one freed up.
It's a story that I am a little embarrased over really ... having had the boat for years in UK literally barely used ... it is only now that I have her at home in Baltic and close enough to do such work. But of course those years idle have added to the original problem.
 
I think you're on a hiding to nothing...

The (stainless) shaft is likely to be pretty well corroded onto the aluminium casting - use of heat would help; and lots of penetrating oil. If you apply the penetrating oil while it is hot, then as it cools it'll soak in a bit.

Don't use a bolt as a replacement shaft; the thread will damage the inside face of the block, particularly when under a high load.

What is the likelihood of just replacing the whole bottom fitting?
 
I suggest that you take the whole sheave and base assembly out of the mast so that you can work on it on the bench in comfort. [You may find that the mast extrusion is badly corroded so that may need repair, or shortening until you reach sound metal.] To get rid of the salt deposits I would boil the assembly in fresh water, changing it several times. Then apply PlusGas or similar penetrating fluid and let it soak in. Some heat might help but beware of melting plastic bits. Make sure your screwdrivers fit the slots in the screws perfectly and if you need to drill any fastenings out you must have a sharp center punch and drill. Try and tighten the screws a fraction before you try to unscrew them. And don't be in a hurry.

When all that has failed go and order a new mast!
 
I would remove the plates first and have a look at the pins. This might sound daft but on one mast in my experience they were Tuffnol and the ally sheaves had a Tuffnoll bush in the center. If they will drive out then fine but if not I would drill them out. You don't have much to lose doing this because you can rebore the sheave centres easily and open up the holes in the mast foot to match whatever you plan to use as a replacement pin. Accuracy in centreing the drilling is also not super critical because you are not talking about a rapidly revolving component. I t just has to turn easily and not have too much play in it. I am not suggesting being careless with it just that it is not that critical.
 
[ QUOTE ]
I would remove the plates first and have a look at the pins. This might sound daft but on one mast in my experience they were Tuffnol and the ally sheaves had a Tuffnoll bush in the center. If they will drive out then fine but if not I would drill them out. You don't have much to lose doing this because you can rebore the sheave centres easily and open up the holes in the mast foot to match whatever you plan to use as a replacement pin. Accuracy in centreing the drilling is also not super critical because you are not talking about a rapidly revolving component. I t just has to turn easily and not have too much play in it. I am not suggesting being careless with it just that it is not that critical.

[/ QUOTE ]

This sort of goes with my thinking ... the sheaves are load bearing of course - the halyard comes round them and up to the cleats. BUT they only turn at slow speed as you heave / lower sail. In fact the ones in question are only used occasionally - the often used are free and OK.

I am extremely reluctant to remove the casting from the mast foot. All looks and feels fine ... and I feel I may anger the gods if I disturb it !

Other problem of course .... temp out there is -10C ..... not the best to work in on such an item ... metal is VERY cold to touch and it's no fun trying to work with gloves on ....
I think during the next month or so as temps cont. as now ... I will keep dosing down with penetrating oils etc. - see if they slowly attack the crud ... even to soften it enough to allow me to pick away at it ...

It would have been interesting if I could have got all the way round the sheaves ... to fit a strap round and like a filter key - turn the sheave !! But can't get round back to feed the strap - tried ...

I reckon once the crud is cracked around the sheave - it will then start to break away and free up. But I can't get a blade or anything in there to work at it ...
 
A classic way of getting some of the crud removed from round the edge of the sheaves is to break a razor blade in half and notch the cutting edge and then hold it in a pair of molegrips and saw gently back and forth, When you.ve got down to the shaft you can then use the back side of the blade to scrape out the bit behind the shaft. You then have room to move the sheave on the shaft and release the shaft . It generally best to re-drill the mast and sheave to accept the next size of pin up to ensure you get a good bearing surface. Lap it in with some T-cut and it'll last for the next twenty years . /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
 
May be a bit too aggressive but could you feed a bent wire around and back out to use as a threader for something like the flexible carbide coated cutting wires you can use in a full size hack saw. You might be able to gently draw one back and forth down each side of the sheave.

This kind of thing.

I would be worried about the increased brittleness of the casting in those low temperatures to do anything that would stress the casing.
 
I'd leave them well alone any force on that casting and it'll self-destruct.

Cut slots in the mast and lead to turning blocks.
 
[ QUOTE ]
May be a bit too aggressive but could you feed a bent wire around and back out to use as a threader for something like the flexible carbide coated cutting wires you can use in a full size hack saw. You might be able to gently draw one back and forth down each side of the sheave.

This kind of thing.

I would be worried about the increased brittleness of the casting in those low temperatures to do anything that would stress the casing.

[/ QUOTE ]

Fuels and temp ..... no problem - I know what happens ... but Metalurgy ?? It's one of the thoughts that went through my mind - strike with a hammer and "CRACK" .... not only cold but being mid 70's boat ... mast could be a lot older ??? Boat was home completed like many were - so could have been 2nd hand mast then ???????

When weather warms up a bit ... will try and look at the pins ... but I seem to recall they were stainless or shiny metal anyway !! Loads of penetrating oil ...........

Like the razor blade idea - but I wonder if its a bit far gone for that ... wondered about a stanley blade .... but still need to get sheave turning .....

Lots of ideas coming out ........... I'm sure I'm not the only one with this problem ... (maybe only one trying to do it in such winter temps though !!)
 
I'm no engineer but I'd be very reluctant to try and drive out the pins with a hammer and drift.....good chance of cracking something. Like a previous poster I'd personally try hydraulics, perhaps in the form of a bottle jack. If you don't want to remove the base fitting from the mast, I'd try and get that end of the mast into a position between 2 rock solid places like brick/concrete walls. Pad out the excess distance with concrete blocks, piece of wood and a socket to accept the pin as it drives out (hopefully), sacrificial brass(?) drift between jack and S/S pin. Put it under pressure and apply heat/freeing oil, etc. If anything goes wrong it should be the brass that suffers and not the mast. Maybe invite local small engineering outfit over for a beer and advice?
 
[ QUOTE ]

don't mess with it, cut slots and use turning blocks, likely to cost about the same and you won't risk angering the gods

[/ QUOTE ]

This is not first suggestion to do this and I am intrigued ... as this is the base of mast and the slot you see is the one that sits on the mast base fitting on deck .... and all halyards are internal .... I'm trying to get my minds eye to visualise such blocks etc.
 
Forum advice...

[ QUOTE ]
This is not first suggestion to do this and I am intrigued ... as this is the base of mast and the slot you see is the one that sits on the mast base fitting on deck .... and all halyards are internal .... I'm trying to get my minds eye to visualise such blocks etc.

[/ QUOTE ] You're surely not expecting practical suggestions on the PBO forum?
 
Re: Forum advice...

[ QUOTE ]
[ QUOTE ]
This is not first suggestion to do this and I am intrigued ... as this is the base of mast and the slot you see is the one that sits on the mast base fitting on deck .... and all halyards are internal .... I'm trying to get my minds eye to visualise such blocks etc.

[/ QUOTE ] You're surely not expecting practical suggestions on the PBO forum?

[/ QUOTE ]

Well naive it may be .... but yes !! /forums/images/graemlins/smile.gif

It may be an answer - but having trouble seeing how it could be done ... cut slot and fit block ........... but surely the slot is already there - its just caked up with a stuck sheave.
I'm pretty sure I can't drill out the pins as I think they are stainless .... the casting looks as though it might not take physical abuse such to get the pins to move .....

I could in fact ignore the whole thing and carry on with as is ... blimey it's been that way for long enough ...

I'll probably end up as another says - calling in a local engineering guy to have a look and dabble at it .. after I've exhausted the penetrating oil routine !
 
Re: Forum advice...

Hello Nigel my guess is that you have 2 corrosion problems one being the pin into the casting and the other being the sheave onto the pin. Apologies if I have got it wrong.

Also of course you will have the base fitting corroded into the mast. The latter being best left well alone. If you decide to remove the casting the best bet is to decide to sacrifice a few inches of mast and basically cut the mast off then cut through the mast material attached to the fitting and try to peel away the mast material.

I think I read that you can't get a piece of rope around the sheave. If you could a rope will give a good grip on the sheave if it is twisted tight to make a good grip the twist could be spoken to with a large hammer to possibly break the corrion of the sheave onto the axle. it is worth trying if possible cos it would solve the problem easily.

Anyway assuming you decide to leave the fitting in the mast and you want the shaft pin out then I would suggest you need to destroy the sheaves by drilling and chiselling. Actually a cold chisel (I gather everything is cold) on the edge of the sheave may get some turning and if not may well be the beginjning of smashing the sheave. If you don't get the sheave out of the way you will have a corrosive join of the pin into the sheave as well as the pin into the casting and as the sheave is virtually joined to the casting you will have little chance of breaking all corrosion joins at once. Once the sheave is out of the way then you have a corrosion join at each end of the pin where it fits in the casting. You may even be able and willing to cut the pin in half so you are only dealing with one corrosion join at a time. Heat on the casting may be the best way to get movement.

I would think that the hammer bash would be as good as hydraulics however you should try to warm the casting before you bash the pin. You may have access to that chalk or pencil used on aluminium to indicate temperature when welding ie before it goes too soft which would allow you to get a good high temperature confidently.

Old age is a bugger for sailors and for masts so good luck olewill
 
You must log in or register to reply here.

Share this page

Top