Tolerenace for Propeller Shaft Alignment

Discussion in 'Downeast Engine Room' started by PatrickPresti, Jun 10, 2019.

  1. PatrickPresti

    PatrickPresti Captain

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    Hi Guys,

    What's the tolerance specifications for a propeller shaft to transmission coupler alignment?

    Thanks,

    Pat
     
  2. Genius

    Genius Captain

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    I usually settle on 0.004".
     
  3. Gurryman

    Gurryman Captain

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    .001" for each inch of flange diameter. I usually get them under .002"
     
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  4. PatrickPresti

    PatrickPresti Captain

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    Gotcha. I think a ZF 63a has a 4" diameter flange...
     
  5. ARC

    ARC Senior Member

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    All are in agreement. That’s a first
     
    ARC,
  6. PatrickPresti

    PatrickPresti Captain

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    It's getting lined up this weekend...
     
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  7. mike@mpi

    mike@mpi Senior Member

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    Center your prop shaft in what ever stuffing box or shaft log you have coming through the hull into the engine room. In my case I have a 2" shaft tube and 1.5" shafting so I centered the shaft using four 1/4" strips of rubber. Set the gear output flange so it's right in line with the shaft and then pull the prop shaft up onto the transmission output shaft pilot. When it's close enough to easily measure with a feeler gage you want to set the flange face to face tolerance to .001" for every inch of shaft diameter plus .002" built in tolerance. Basically if I have 2" shafting and it's flange deviation is .005" or less it's going to be OK. I just don't want the whole engine/gear package offset to the side or up and down enough that it's stressing the prop shaft seal.
     
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  8. PatrickPresti

    PatrickPresti Captain

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    I got Up and Down and Left and Right between .025" and .003". I am going to try to get it a little more closer in tolerance...
     
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  9. Toolate

    Toolate Captain

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    Rotate the shaft 120 degrees and do it again. Then do that again so you have checked it 3x in 3 diff positions.
     
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  10. Diesel Jerry

    Diesel Jerry Captain

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    Not to be captain over achiever but if you get it in spec don’t just stop there. Get it as close to perfect as you can.
     
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  11. PatrickPresti

    PatrickPresti Captain

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    Okay
     
  12. PatrickPresti

    PatrickPresti Captain

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    What?
     
  13. Diesel Jerry

    Diesel Jerry Captain

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    Lets say you have a 5” coupling. Don’t get it to .004 and just stop. Sometimes with a little patience you can get it to .002 or better.
     
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  14. PatrickPresti

    PatrickPresti Captain

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    Understood. Thanks.
     
  15. Toolate

    Toolate Captain

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    Are you a “check it again in the water” type of guy? I have done in a few times and not seen any difference so I think I am over it but if I had an old/flexy boat I would probably do it.
     
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  16. Diesel Jerry

    Diesel Jerry Captain

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    In most cases yes. I do a lot of sail boats here and you wouldn’t believe the change from no mast to mast that is fully tuned. Some don’t change. All depends on how the boat is built. How the boat’s block and stands are.
     
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  17. Genius

    Genius Captain

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    ....then you start your engine that sits on soft mount and your alignment goes to sh#t.
     
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  18. Diesel Jerry

    Diesel Jerry Captain

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    It is funny to see an engine move around, then you start to wonder why was I so anal.
     
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  19. toolmaker

    toolmaker Senior Member

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    Patrick
    ---everything that the boys have stated is great info, BUT lets never forget the machining accuracy of the couplers themselves and the shaft and keyway. When I built my last twin screw Carolina boat a few of my incoming QC inspection holds were on these specific components [learned from previous nightmares] and both were found to be no where near what I considered even close in my world. Everything was boxed up and air freighted to my shop and reworked to perfection; makes assembly and alignment a heck of a lot easier and accurate with minimum drive line vibrations due to excessive individual component tolerances as a result of manufacturing sloppiness and no accurate inspection.
    Always a lot of variables to deal with of course when setting up the drive line.
    Jay
     
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  20. PatrickPresti

    PatrickPresti Captain

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    Jay,

    I totally agree. Before I removed the engine, the boat ran smooth and was vibration free. I am still using the same gearbox, shaft, and couplers so I know it wasn't an issue beforehand. I will keep you posted with how I make out. Thanks for your suggestions.

    Pat
     

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