have I ruined another prop?

Discussion in 'Props' started by the brain, Aug 20, 2017.

  1. the brain
    Joined: Sep 2016
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    the brain Senior Member

    something bumped my alumimin props center section.

    can I test this prop for out of balance?

    I certainly don't want to ruin the prop shaft seals.

    I actually have ordered a new prop. (still dialing in for perfect RPM) would like this as a spare stowed.

    edit can I heat and bend w/ crescent wrench?
    Thanks TB
     

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  2. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Not sure if your prop has a rubber hub but the application of heat might ruin the hub. If it does not, you must remove the prop so any heat application so that the heat will not damage the seal, any rubber on the bearing seal if it has any.

    If you heat the aluminum with a torch you really should know what you are doing as the melting temperature is quite low and you run the risk of the bent part just melting off the hub. Welding supply shops sell "temp sticks" which looks like a marking crayon, you heat the aluminum and wipe the crayon with the appropriate temperature rating and if it is that temperature or above, the crayon will melt.

    The aluminum has obviously bent to this position so it MIGHT be able to be bent back to the original shape without heat. That being said as it has deformed, the material that is bent has been stretched beyond its elastic limit and has strain hardened to a degree. Ie got more brittle due to the permanent deformation and might not take the reshaping without cracking. But you have nothing to lose. If there is no rubber in the hub, a tig welder would be able to build up enough material that you could grind back to its original shape

    If you put a crescent wrench on the bent portion, it will certainly impinge on the thinnest part of the bent portion and probably break.

    So if it were mine, I would take two hammers, one as backing and the other, ball peen, and carefully tap the bent portion back into place. If it works you have saved a few bucks, if not you need a prop shop to deal with it.

    Alternatively, take it to a prop shop and let them bang it straight

    Alternatively, maybe you have a body shop guy who has the dollies to help in the straightening process and it might cost you a beer.

    If you can get it pretty straight, keep it as your spare, or keep it as a spare as it is now. The small amount of material that is not concentric with the shaft and does not mirror the other opposing side, will not cause any damage for short term use as it is close to the shaft and light weight. Low rpm, light weight, imbalance material close to the hub, as a get home prop, will be fine
     
  3. the brain
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    the brain Senior Member

    yes the hub is rubber. this a new prop. used very little

    thanks for advice TB
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    "bumped the prop centre section" ? I don't follow what has occurred there. Of course there is a rubber hub there, so applying heat to the hub is not a good idea.
     
  5. gonzo
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    gonzo Senior Member

    Looks like you backed into something kind of hard. You heat it a bit and use a hammer and backing iron to straighten it.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I see what you mean, should have expanded the picture ! No problem with the rubber.
     
  7. the brain
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    the brain Senior Member

    fixed this prop. w/ pair of pliers 14.25x21 pushed vessel to mid 40knts

    my repair isn't perfect what do you Guys think will this prop vibrate?
     

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  8. JamesG123
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    JamesG123 Senior Member

    You should also check run-out with the prop installed to make sure the prop and shaft are still within tolerances. Otherwise the seals and bearings will be the next to go.
     
  9. the brain
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    the brain Senior Member

    I think you're correct, an out of balance prop will wear out seals.

    How can I tell if this prop is usable just run it and hope it doesn't vibrate ? thanks TB
     
  10. JamesG123
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    JamesG123 Senior Member

    Not so much just out of balance, but out of round or bent shaft.

    You need a dial gauge. Any shop will have one if you can't borrow one, or pick up a cheep Chinese one from Harbor Freight etc.
    [​IMG]
     
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  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Aluminium props are light, just run the thing, I don't think you will have too much to worry about, but if as you say, vibration becomes evident, then you might have to do some more (better) panel beating.
     
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  12. the brain
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    the brain Senior Member

    is this a prop. shaft being measured? how far can needle be allowed to move?

    the fins are fine. just the middle is/was dinged.

    currenty my 14.25 x 19 =38knt at 6200RPM
     
  13. baeckmo
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    baeckmo Hydrodynamics

    Support Mr E here; the bent part is easily (as with a small force) bent/deformed. That force wouldn't normally affect the shaft.
    A tip on temperature checking: When a soft wood stick (say pine) makes a brown track on a hot surface, it is slightly above 300 C, allowing reshaping most common alu alloys. Note that the "aging" of the prop alloys to reach adequate strength again takes time.
     
  14. JamesG123
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    JamesG123 Senior Member

    That was just a generic pic of a dial gauge I found on the interwebs. The runout specs will be on the motor's mfg. owner/service manual. I was just suggesting what any competent boat shop would/should do when fixing a prop. Feel free to run er til' it starts making crunchy noises. :)
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    those old Johnno boxes are pretty durable, I would not lose sleep worrying about
    the dinged prop hub, you see some horrible looking alloy prop blades that are bent and uneven, and that is more likely to cause problems than what you are looking at.
     
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