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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 08-03-2009
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Vibration / Alignment

I have had a drivetrain vibration since I launched this spring. Over the winter, I replaced or added the following.

New Cutlass Bearing
Shaft trued up
Propeller (fixed 2 blade) pitch re-tune (to spec)
New R&D split half shaft coupling (keyed to shaft)
New R&D drive saver coupling
New PSS seal

Syptoms I've noticed:

Noticable driveline vibration in gear at varying RPM. It seems to smooth out at 1200 and 22-2400 RPM. Anything above 2400 sounds and feels like the boat is going to shake itself apart.

Under sail, with the propeller freewheeling in neutral, I can hear a clunk with each shaft rotation. Locked in reverse, this goes away.

I've spent a few hundred bucks to have the local yard check the alignment and declare it within tolerance. My understanding is they unbolted and removed the drivesaver, pushing the the half couplings together and measured the alignment. I'm concerned about the precision and attn to detail with the yard (they don't like working on my boat 'because it's tight and hard to work down there')

I don't know where to go next. I would like to try to narrow the area of concern to prevent spending too much investigative $$$, either with my normal yard or another in the area. The regular yard wants to do motor mounts next...which I am not sure is the problem. I did not have the symptoms when I hauled out last year.

Thanks in advance.

Jason
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Old 08-03-2009
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When you say that the shaft has been "trued up" are you saying it was checked for straightness? 25 yeas ago I owned a Hunter 27 that had a lot of drive train vibration. THEN I dropped a sheet over the side at night and caught it in the prop, bending the shaft about 20 degrees and nearly ripping the strut completely out of the boat! I didn't have the money for a new shaft, so I straightened it myself by pressing it and rolling it over a surface plate. I then lined up the strut, shaft and engine using feeler guages. I was hoping for only a little worse vibration than before. I was shocked when the sucker ran smooth as silk! Everyone who came aboard was amazed at how smooth it ran.

Gary H. Lucas
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Old 08-03-2009
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Yes, checked for straightness. It was in good shape.
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Old 08-03-2009
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Ideas

Here are some ideas, in no particular order:
  1. Growth on the prop - Have you noticed the vibration since day one or has it gotten progressively worse. If worse, could be growth.
  2. Engine mounts going? Can you have some one work the throttle while you look at the motor? If so check the vibration as the throttle revs. Check the tightness o f the motor mounts and the whether the mounts are solid.
  3. Check the motor out of gear with the throttle. If you rev the motor in neutral, do you feel the vibration.
  4. If the vibration has come on suddenly, could you have thrown a shaft zinc or a piece of one?
  5. Something wrapped on prop shaft?
  6. Put the motor/shaft in neutral and turn it by hand, is there any binding or looseness?

DrB
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Old 08-04-2009
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Try running engine in gear without the prop.
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Old 08-04-2009
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Good ideas, thanks.
Quote:
Originally Posted by DrB View Post
Here are some ideas, in no particular order:
  1. Growth on the prop - Have you noticed the vibration since day one or has it gotten progressively worse. If worse, could be growth.
  2. Engine mounts going? Can you have some one work the throttle while you look at the motor? If so check the vibration as the throttle revs. Check the tightness o f the motor mounts and the whether the mounts are solid.
  3. Check the motor out of gear with the throttle. If you rev the motor in neutral, do you feel the vibration.
  4. If the vibration has come on suddenly, could you have thrown a shaft zinc or a piece of one?
  5. Something wrapped on prop shaft?
  6. Put the motor/shaft in neutral and turn it by hand, is there any binding or looseness?

DrB
The vibration has been there since Day 1 of this season, the prop was clean. This engine ran in gear like a Lexus commercial with the pyramid of wine glasses on the hood last year. This is definitely in the drivetrain.

I will look at the mounts and their tightness.

No vibration with the motor rev'd (to max RPM) in neutral.

Boat was short hauled in the last couple of weeks to replace a seacock at the same time the yard tried to 'diagnose' the vibration. Zincs were good and nothing wrapped on the shaft.

I will peform the test for binding, looseness, but since the yard de-coupled and re-coupled the shaft, coupling and transmission....I am fairly confident there is no loosenes. I also crawled down there last week and put a wrench on all the coupling bolts....tight.

Thanks for the feedback.
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Old 08-04-2009
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Quote:
Originally Posted by trantor12020 View Post
Try running engine in gear without the prop.
OK. If the vibration goes away....what does that mean?
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Old 08-04-2009
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No Prop, No Vibration

My guess is that if you can take off the prop in the water and run the engine and turn the shaft and the vibrations significantly reduce, the prop could possible have one of the following issues:
  1. One side pitched more than the other
  2. A damaged blade (one or both)
  3. Prop not centered on shaft
  4. Prop loose
  5. Prop unbalanced

When you take the prop off and the vibrations still exist, you have to look at the shaft, CB, strut, tranny, etc. Remember, when the tranny is in neutral the shaft and the motor are decoupled, so if the gears are shot, they maybe causing the vibration. However, usually a blown tranny has slippage and problems going in and out of gear, not what you describe.

DrB
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Old 08-05-2009
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Quote:
Originally Posted by jason3317 View Post
OK. If the vibration goes away....what does that mean?
that means its probable the prop is off balance as the prop had been repitched/rework prior to launching.
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