Latest News: Forums Technical sticking sheave

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  • #4247
    waveney
    Participant

    Apologies if this is an old chestnut, but I could not find a relevant thread elsewhere..

    My lower mast sheave (triple block near the foot of the mast – sorry if terminology is wrong) is jammed and I was looking for a way to repair or replace. It has a coiled rivet type pin running through the blocks which has no obvious means of removal for cleaning. Would it be easier to fit a new mast plug in it’s entirety?

    Any help very welcome indeed.

    #9767
    Colin Parkstone
    Participant

    Not always, the new type is wider and fits the tabanacle to well.

    Try taking the heel off the mast and remove the lead rivet with a large bolt the same size as the rivet so as not to spread the rivet.

    Your find the sheaves will be coated with mud and salt, clean off and pass a file across the faces of each one.

    Then return to the heel but put the best sheave for the genoa halyard as it takes the most load.

    If the screws into the heel are not good and loose, maybe redrill in a new place for a better fit.

    Done!!

    CP

    #9768
    waveney
    Participant

    Thanks, sounds good – will I be able to re-use the lead rivet? seems a strange device to me but I am sure there is a very good reason for it’s use. From what I can see it is a rolled piece of lead and I would have imagined that it is qute difficult to bang this through the sheaves without bending it.

    I am sure I am missing somthing but I am keen not to wreck my new boat!

    #9769
    Colin Parkstone
    Participant

    Yes you can, your be fine ! It will come out ok if your carefull. CP

    #9770
    Dave Bevan
    Member

    @waveney wrote:

    From what I can see it is a rolled piece of lead and I would have imagined that it is qute difficult to bang this through the sheaves without bending it

    I very much doubt it is lead, it will be a roll, or spring pin. You should be able to drive it out as Colin describes – just make sure the mast heel is firmly supported on a block of wood or similar that will absorb any shock from your tapping, and make sure the drift you use to drive out the pin is just slightly smaller than the hole. You shouldn’t need to remove it completely, just far enough to release the sheeves.

    #9771
    waveney
    Participant

    Thanks evreyone, I shall have a go today; Invaluable advice.
    I must say I had not come across rolled pins before but have now ‘googled’ them and understand what they are for. I found this short piece which may interest others:

    The spiral spring concept represents broad design
    latitude in the control and development of pin
    fl exibility. The engineered fl exibility of Spirol® coiled
    pins provides for compression of the pin into the hole
    and for continued fl exibility after insertion. Without
    this fl exibility, the total load applied to the pin would
    be transmitted to the hole wall without dampening
    the impact. Since the hole material is normally softer
    than the pin, elongation or enlargement of the hole
    would result. The fi t between the hole and the pin
    would become loose, increasing the impact force and
    accelerating the rate of hole damage. The inevitable
    result would be premature failure of the assembly.
    In properly engineered applications, the fl exibility of
    Spirol® coiled pins dampens shock and vibration, thus
    eliminating hole damage on all the components of the
    assembly resulting in maximum product life.

    #9772
    Colin Parkstone
    Participant

    I understood that, I think? Wonder why its not used in any other pin on the mast like genoa and main halyard sheaves, ?
    CP

    #9773
    Swiebertje
    Participant

    Because these springs are made of hardened steel that will rust in no time.

    Are you sure they used a spring pin in the mast foot? In my mast’s foot it is a stainless steel pin, not a (blue) steel spring, but it does have a tight fit. So tight it has to be driven in and out by punch and hammer as you described earlier. I stock several boxes of spring pins but I have to store them with a thin film of oil to prevent them from rusting, despite they are kept indoors in closed cardboard boxes that are in a dry and warm cupboard.

    Maybe that is the root cause of the problem? Someone at some point in time lost the original stainless steel pin and replaced it with a spring pin? Then, over time this pin started to rust preventing the sheave from running smoothly?

    #9774
    Colin Parkstone
    Participant

    Bert,
    You may have the new type heel which is a plastic type, that has the solid pin in it held in with Blue triangular covers, unlike the older alloy type that has a rolled or other type pin.
    CP

    #9775
    waveney
    Participant

    Well, progress has been made. I couldn’t remove the plug as one of the bolt heads sheared off. I will try and remove it with a stud extractor later on, and then replace the three machine screws (if I can find replacements)

    I decided to try and remove the spring pin in situ, and it actually came out quite easily (just as Colin had said). There are some deposits on it, but it is not rusty so must be of stainless construction. The sheaves are quite burred so I will replace them and hope for a good result. The pin, once removed, is a loose fit through the sheaves which were actually stuck against the sides of the mast plug so I will clean the inside of this with some wet and dry and then oil.The mast plug is alloy.

    Thanks again, Seb

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