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Wobble in port shaft

Discussion in 'Post Yacht' started by Stainless45, Jul 16, 2021.

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  1. Stainless45

    Stainless45 Active Member

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    So my port shaft has some wobble to it. It isn't massive like a bend, but you can see it when it's rotating and there is some vibration at speed. No leaks from the dripless packing. 6v-92, Twin Disc MG 509 gears. Got my diesel guy coming next Friday to have a look. We tried to measure it in shipyard and came up with about .070

    I'm looking for feedback from those who have done an engine alignment (assuming it's not bent)

    And with a wobble like that how much am I risking tearing up the gears by running the boat?

    Thanks
  2. mapism

    mapism Senior Member

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    TBH, I would call "massive" any shaft wobble that you can spot by eye.
    In your boots, I wouldn't even start checking engine alignment without pulling and checking the shaft, first and foremost.
    BTW, you don't mention how old the boat is and if/when shafts were last checked, but considering the engines I guess she's no spring chicken...
    So, it wouldn't be a bad idea to check both shafts, not just the wobbling one.
  3. Capt Ralph

    Capt Ralph Senior Member

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    If you can see a wobble, imagine what the output flange on the clutch feels.
    Marine gears can loose their loading bearings with any wobble.
    There is a factory max runout spec, at the coupler face, max 0.004" .
    Last edited: Jul 16, 2021
  4. Stainless45

    Stainless45 Active Member

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    While in the shipyard we noticed the shafts were both center punched in the prop end, 5 punches like you would see on a set of dice. I don't know if they had been previously straightened, or what this means. Yes the wobble is visible to the eye, and the boat is 1990

    She's in the water currently,
    Last edited: Jul 16, 2021
  5. mapism

    mapism Senior Member

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    No idea of what the punches mean, but it might as well be done from the factory on all new shafts.
    If you are unsure of if/when they were ever pulled and checked/straightened, it's something worth doing on a 30 years old boat.
    Possibly taking the opportunity also to replace bearings and check/refurbish the seals.
  6. Matt46post

    Matt46post Senior Member

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    What ever you do don’t let these fools Platypus Marine touch your shafts
  7. DOCKMASTER

    DOCKMASTER Senior Member

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    How long have you had this vibration? Is it a fairly new issue? How/what did you measure that you got .070”?
  8. SplashFl

    SplashFl Active Member

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    Make sure when an alignment is done she's been in the water a day or so. A yard that once did mine on land found themselves doing it again a day after back in the water.
  9. mapism

    mapism Senior Member

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    Very good question.
  10. Stainless45

    Stainless45 Active Member

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    It was a rough measurement we made with a fixed micrometer while rotating the shaft. She's been in the water a couple months. Anybody have experience doing an engine alignment on these? If the mounts are bad where do I source those?
  11. Pascal

    Pascal Senior Member

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    If you have that much wobble I don’t think an alignment will fix it. The shaft will have to come out and either be straightened by a good prop shop or replaced.

    Don’t run it like that above 1000 rpm or you will damage the gear.

    shafts are not that expensive you may consider replacing it. Get a price from a good prop shop.

    when I repowered my 53 hatt a couple of years ago, I put new shafts. That was a corner I didn’t want to cut... and on the 53 MY, they are 20’ long !!
  12. mapism

    mapism Senior Member

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    Forgive me if I insist, but I fully agree with Pascal on this one.
    It's pointless to start thinking to replace the engine mounts, because as I said in post #2, you really don't want to waste time in a a re-alignment without straightening the shaft first.
    No matter how good your reasons for thinking that alignment is the culprit, by now you have ALSO a shaft problem, whether you like it or not.
    When running a boat with a bad alignment, something has to give, and you'd better hope it's the shaft, because the alternative is the gearbox...
  13. Oscarvan

    Oscarvan Senior Member

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    Amazing the engineers got them to run straight. Mine do.... knock on wood.
  14. Stainless45

    Stainless45 Active Member

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    I appreciate the replies... since the boat is in the water I'm not going to be pulling the shaft any time soon. Going to see what can be accomplished with an engine alignment since the engines were put in by the previous owner and I don't know if they were ever properly aligned.
  15. Pascal

    Pascal Senior Member

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    Well originally they were two piece shafts with a coupler. When I went to one piece I discussed it with the prop shop and they agreed single piece would be better
  16. Pascal

    Pascal Senior Member

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    frankly there is nothing special about a 34 C. Find one without this issue unless this is a great deal. You don’t know what damage was done running that way.

    and I still believe a boat that get damaged from a line around a shaft is suspect
  17. DOCKMASTER

    DOCKMASTER Senior Member

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    So that .070 you measured with a micrometer while rotating the shaft, where on the shaft were you measuring? Up near the coupling, down by the shaft log/seal or in the middle? Do you have any reason to suspect a bent shaft? Did you hit something? I would be a bit surprised if you damaged the gear but it certainly can and does happen. What size shafts are they?
    Getting the alignment checked first is a good move since you are in the water and sounds like you prefer not haul or don’t have plans to currently. You really just have to do a process of elimination.
  18. Capt Ralph

    Capt Ralph Senior Member

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    Oh the taps on the shaft end? This end out.
    Probably a double taper shaft and it helps the shop know what end is the prop end.
    After one of my shafts was cleaned up, It was real hard to tell.
    Stainless45 likes this.
  19. Stainless45

    Stainless45 Active Member

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    The measurement was back at the seal, the coupler doesn't have any movement. I have a video but I don't think I'm able to post it. Didn't hit anything, got the boat like this. 2" shafts and no evidence of any strikes while she was in dry dock. Going to see on Friday where an alignment gets me to. As you said process of elimination.
  20. Capt Ralph

    Capt Ralph Senior Member

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    Measuring at the log and finding 0.070" wobble can be serious.
    But, I can also see an alignment issue causing a D bend or shaft whipping.
    Also, poor coupler facing, poor coupler attachment, poor alignment to the support bushings.
    Question; Is there a bushing in the shaft tube?

    Give a multi point alignment a try. If your confused with that comment, e-mail me.