I need to change my shaft hub coupling

Discussion in 'Powerboats' started by sdowney717, Jul 21, 2015.

  1. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    I was working on engine alignment and saw that it is too loose on the shaft.
    I plan to do it with boat in the water, there is a lot of room to slide shaft back.
    Going to put an exhaust clamp on the shaft to secure it so it cant slip out of the packing. Although I think it cant since the prop will hit the rudder first.

    The replacement coupling is used but better than the one I have. I measured with a digital caliper and it is right at 1 3/8. If it is also too loose, then I will get a split coupling. The one I need is this which seems to be a good price.

    http://nop.deepblueyachtsupply.com/split-marine-transmission-coupling-50500s1375
    And here is a master list.
    http://catalog.buckalgonquin.com/vi...essories-transmission-couplers-split-couplers

    Sadly every coupler I might end up using, has a different bolt pattern. The replacement coupler the bolts are in a Y pattern with the key, which I like.
    My current coupler the bolts are 180* apart and 90* from the key, which I don't like much.

    The split coupler, uses one bolt 180* from the key.

    Getting the old coupler off will be easy as it is greased and not rusted in place.
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Couplers should have an interference fit. That is, they need to be pressed or pounded in for a proper fit. If you can install or remove yours easily, it it too loose. This, of course, does not include split couplers.
     
  3. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Yes, I know needs to be tapped on. I used a 3 lb sledge, levers, and wedges and exhaust clamp to get it replaced today. The old one was too loose, easily tapped off, I could tell when I was aligning the engine to the shaft.

    This 'new' one I got for free. It was replaced due to some people will always buy a new coupling when they work on their shafting.

    I cleaned it up and primered it, the bore is in good condition. The bolts are in a better arrangement and it is bigger than my old one, it is .25 inch longer and the flange is thicker.
    I coated everything with moly grease to keep away rust and make it easier to put together.
    I am extremely happy it fit so nicely!

    Here are some pics.
    Original coupling, bolts out, slid back. You can see the retaining bolts are 180*, how dumb is that.
    [​IMG]

    Exhaust clamp tightened on. This is 1/38 shaft, clamp is 1 1/2, it worked great to hold the shaft. They make a 1 3/8 exhaust clamp, but I would have to order it.
    [​IMG]

    Old one is off. Shaft surface under hub is in perfect shape.
    [​IMG]

    Comparing them, the grey one is much bigger. The flange is smooth, I had just filed the primer to feel if it was flat.
    [​IMG]

    New one is in place! I had to reset the clamp one time, not for slippage, but this new hub is longer.
    [​IMG]

    Nice sharp bit to to drill the SS shaft for the bolts, about 1/4 inch max, dont go any deeper. I think I went 3/16 inch. Use end of file to compare hole to hub edge to see how far in I went.
    [​IMG]

    All done now. I greased up a tap to chase the metal filings, they will stick in the grease and come out the hole.
    [​IMG]

    I ran a die down the bolt threads. The square head bolts are like a grade 10 bolt, one needed the end cleaned up due to being squashed, likely from the loose coupling moving - walking a little on the shaft, and glad I did that. Even the hard tap had trouble cleaning up the bolt end, but afterwards it threaded in smoothly to the coupling.
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Looks good. If the other one was loose it would probably cause some problem later on.
     
  5. pdwiley
    Joined: Jun 2008
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    Location: Hobart

    pdwiley Senior Member

    So..... let's see if I understand this.

    The *only* thing holding that hub to the shaft is the 2 set screws into the shaft, and the only torque transfer is the combination of interference fit and the shear strength of the engaged portions of the screws?

    No keyway in the shaft & hub?

    PDW
     
  6. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    If you look at the photos, it shows the keyway.
     

  7. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Yes, it has a big SS key.
    Those bolts are still very important, consider they bear the prop thrust forward and back.
     
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