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loose prop

Discussion in 'Props, Shafts & Seals' started by Beau, Jul 6, 2015.

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  1. Beau

    Beau Senior Member

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    Hi Folks

    So every year I have to tighten my prop nuts at least several times. My theory is that I have such torque in reverse, that they work themselves free. We have tightened them with a breaker bar, they still loosen. Any ideas on a solution? I was thinking of changing out the nuts, even though they look fine. I have had the props and shaft journals rematched also
  2. Bill106

    Bill106 Senior Member

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    Many possible causes and solutions; Try dry fitting without the keys and marking how far the wheel goes up on the taper (without torqueing or using the nuts, just slip them up), then installing the keys (making sure they don't slide up too far in the keyway), the wheels should go back to the marks, if not the key's are binding them. Second possibility, put on and torque the smaller nut first followed by the larger one, doubt it will make a difference but worth a try. Third is to get a Propsmith or similar device to press them in place (and remove them with less struggle!). I have seen yards apply a little goo (4200 or 5200 sealant) on the threads before putting the nuts on but personally wouldn't do that, the next guy who has to remove them won't be calling you "honey"! :)
  3. Beau

    Beau Senior Member

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    Thanks Bill106

    My marina has the larger nut on first?
  4. Capt J

    Capt J Senior Member

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    Smaller nut goes on first. I always lap the props when I put them on, Put them on with the nut a bit loose and spin them with valve grinding compound inside the hubs, pull them back off, clean everything, re-install keyway, put props on, tighten nuts. I've NEVER heard of them loosening because of too much torque in reverse, the keyway should keep any movement from loosening the nuts. Have also seen people put 4200 or 5200 on the threads before tightening the nuts, we never did, but have seen it done. Also sometimes the keyway extends too far into the taper of the keyway slot and doesn't allow the props to go all of the way on, Have had to shorten the keyway before as well on some new boats from a quality manufacturer. You should see this if you mark the shafts as Bill described.
  5. Beau

    Beau Senior Member

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    Thanks Capt J I'll print this and give it to the yard. The prop shop owner is coming tomorrow to take a look for himself. Could it be as simple as having the nuts installed in reverse order??
  6. Capt J

    Capt J Senior Member

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    I doubt it, but you never know. Big nut/small nut you still have 2 nuts. Just guessing, I think the Keyways might be too long and the nut drives them up the taper, not allowing the props to seat themselves all of the way up the shaft. I would, lap the props, clean all of the valve grinding compound out, put the prop back on without the keyway, snug 1 nut and mark where the prop ends up on the shaft with a magic marker, pull it off and then try it with the keyway in and see where it ends up. Also how tight does the diameter of the keyway fit into the prop and shaft.
  7. Beau

    Beau Senior Member

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    Capt.

    I will ask the marina to follow your advice. We just had the props off last fall. The keyways are square and fit well in their notches - seem nice and snug, but I will check their length. Thanks for the good advice.
  8. K1W1

    K1W1 Senior Member

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    In addition to lapping the props with grinding compound you should after cleaning it all off apply Prussian Blue to the cone part of the shaft evenly and slide the prop home to where it would normally sit, once removed any bright bits will be where the prop contacts the shaft.
  9. karo1776

    karo1776 Senior Member

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    A trick or two on K1W1 comment as to checking with Prussian Blue:
    1. Line the shaft so the keyways are horizontal, not vertical either up or down, but it does not have to be perfectly horizontal.
    2. Take out the keyways and clean any noticeable burrs on the keys, and key slots in both the prop and the on the shaft... AND CLEAN PERFECTLY CLEAN THE SHAFT AND PROP MATTING SURFACES... use some light scotchbrite or other to make sure of no rust or anything but bright clean metal.
    3. Apply the Prussian Blue in a light even coating to the shaft... important it is thin and even as possible... this take time to learn but a linen or closely woven cotton (like bed sheet scrap) over a neatly folded rag pre-saturated with the blue (exactly like an ink stamp) with no globs on the saturated smooth sheet surface works or buy an old fashioned ink stamp pad and remove it from being glued down in the tin (Store in tin). Apply to shaft by putting a small glob on the smooth surface of you bluing pad (home made or store bought as I said). Using the pad wipe it on the shaft you will find stippling it on helps evenly get it on... then using wide smooth strokes smooth the thin film of blue on the shaft. TO GET EVEN THIN FILM ON SHAFT.
    4. Slide the cleaned taper on the prop up the shaft by letting it rest on the top or upper surface of the shaft; this will leave a bright line on the shaft wiping off the bluing. When in place snug your nut lightly. Carefully with a Soft faced hammer (lead preferred) tap the prop to free it. Being careful not to move the prop other than to free from the taper. Carefully slide the prop off the shaft with it resting on the top surface, reverse of assembly.
    5. Disregard in "reading the bluing" the line of assembly bring mark.
    6. The high spots will show with clean or bright surface.
    7. These should be smoothed down with a fine small file a Swiss Crochet files work best.
    8. Now some comment about the fit of the taper. The small areas you file even if below the surface and not contacting will make little difference in the holding strength of the taper... there is a large area of contact. That is the thing to remember the taper works by having a large contract area and the slope causes the surfaces to closely mate up. If you only see points of contact those must be worked down to get the overall even close MATING of the surfaces. Remember a few or even many small low or no contact areas like due to pitting will be inconsequential.
    9. Importantly, the key is not the primary part holding the prop from turning on the shaft. The fit of the taper does that without the key. The key is really just there as a backup due to imperfections of the fit. With proper fit the shaft and prop are literally like welded together.

    If you wonder I learned these things as a kid... I attended a military school for a time and they had a machine shop class taught by a semi-retired German immigrant (full master machinist and tool maker in the guild traditions) instructor. I might say NO ONE got a top mark in that class as his belief was that was reserved for perfection. And, secondly I suppose it was about 1960 and my grandfather had his boat hauled and I remember the old guy English guy doing the prop fitting to the shaft in the yard... in those days insurance protections did not include keeping the client or even interested kids away from the work.
  10. Bamboo

    Bamboo Senior Member

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    Are the props loose as well or just the nuts?
  11. Beau

    Beau Senior Member

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    The props become loose also as a consequence of reversing, If I just used the forward gear I wouldn't even need the nuts.
  12. Capt J

    Capt J Senior Member

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    They shouldn't. The Keyway keeps the props locked to the shaft so they can't turn except with the shaft.
  13. Beau

    Beau Senior Member

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    Agreed on the rotational, but if they slip down that fraction of an inch they have that forward and rear motion.
  14. RT46

    RT46 Senior Member

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    my Viking would always have one prop that was loose on the shaft no matter how tight I made the nuts.
    I don't remember which one it was, but every time I was in the water under the boat there was always movement with the prop on the shaft.

    The other one required a great deal of force with a prop remover to take off.
  15. Capt Ralph

    Capt Ralph Senior Member

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    It's all in the surface contact in the tapers. When all is correct and perfect surfaced, you don't need a key.
    Just a lil void in the surface between prop and shaft and it will be loose in a couple of hours.
    RT46 had a great example. one tight and one loose.

    Years ago my diver would report loose stb nuts every three months and tighten them up. Next haul I found the key ways on the shaft and prop were pushed up a bit (fish lip). Probably from running with a loose prop banging against the key. I filed and polished all down, then sent the props in for checking out.
    On return of the wheels, I dyed the shafts again and found the shop had polished the inside of the hub and I lost some contact on the shaft. Laping compound back out, a few more beers and all clean & tight.
    That was 12 years ago, never a loose nut (on my prop shafts) since.

    I will admit only to my close friends here; Yep, I have hit things, logs, Jimmy Hoffa, The bottom of the river and the props do have to come off. My diver does have a few extra words for me now. Those 32" wheels takes da big tool to come off.
  16. Capt Ralph

    Capt Ralph Senior Member

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    If you check into the other web site, Tony describes using epoxy in setting the nuts.
    I think that's nuts but it works for him and his customers.
  17. RT46

    RT46 Senior Member

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    just to add I remember the nuts being loose and up against cotter pin a few times.
  18. Capt Ralph

    Capt Ralph Senior Member

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    That's why that (ever so important part) pin is there.

    During a delivery to WPB and on my own stern-drive boat, IT IS an undeniable feeling (WTF to start) when you call for reverse,,, and it's NOT there.
  19. Capt Ralph

    Capt Ralph Senior Member

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    This also reminds me of another story,, Castle and pin nuts. You may call them crown nuts. Big shaft nuts with slots in them like a Rook or crown, the pin goes thru them and the shaft.

    Pulled a boat with a loose prop and the nuts were still jammed together, top castle nut and pin intact. This was probably the start of my extra time and thoughts in setting props on shafts many years ago.
  20. Bamboo

    Bamboo Senior Member

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    If you use a propsmith to install the wheels and you have lapped them and previously "blue" tested the taper they should not come loose; the nuts or the props.