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Old 07-09-2019, 07:01   #1
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Do Most Yanmars Have a Vibration Range Harmonic

I have a 4JH4E on a Cal 39 MK2. The engine runs smoothly from idle to 1800 rpm then vibrates wickedly until about 2300 rpm then is reasonably smooth to about 2600 rpm. I have a two bladed Maxprop feathering prop.
I have wondered if this is "normal" for Yanmars (a fellow sailor with Yanmar has almost the same range vibration issue).
I would think that if this was a shaft or prop balance issue it would be constant throughout the RPM range.
The cutlass bearing is fine with no noticeable wobble.
Does anyone have any thoughts regarding this vibration issue as it pertains to either the natural harmonic of the boat / engine?
Thank you
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Old 07-09-2019, 07:06   #2
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Re: Do Most Yanmars Have a Vibration Range Harmonic

Could be the shaft, bearing, prop or balance wheel but it’s definitely not normal.
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Old 07-09-2019, 08:00   #3
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Re: Do Most Yanmars Have a Vibration Range Harmonic

My Yanmar has no such thing.


I suspect this is not in the engine, but downstream of there.


I've had some vibration in previous years, which was cleared up with a new cutless bearing. Alignment is also important; as are motor mounts, and prop balance. Here you need a good engineer, and it's NOT normal -- fix it.
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Old 07-09-2019, 08:02   #4
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Re: Do Most Yanmars Have a Vibration Range Harmonic

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I would think that if this was a shaft or prop balance issue it would be constant throughout the RPM range.
That wouldn't be the case because different rpms create different harmonics. A property known as 'resonant frequency' is inherent in all components and just as waves can build upon each other, or cancel each other out, the same can be said of your drive system.

If your Yanmars have no vibration at those rpms when the shaft is not spinning, (tranny in neutral) and occur only when the shaft is turning than you need to look at the shaft system, that being the shaft, bearings, couplers, prop, zincs, etc.

As silly as it sounds changing the shaft zinc may be all that is required to change the harmonics and get rid of the vibration in a best case scenario.
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Old 07-09-2019, 08:49   #5
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Re: Do Most Yanmars Have a Vibration Range Harmonic

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I have a 4JH4E

I have two on my cat, one use to vibrate as you describe, I changed the mounts last winter and the vibration magically disappeared ...
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Old 07-09-2019, 08:51   #6
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Re: Do Most Yanmars Have a Vibration Range Harmonic

I had vibration in my Yanmar 2gm20. I put an old two blade prop that came with the boat and replaced the three year old Acme 3 blade prop. Very smooth, no vibration at any speed.
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Old 07-09-2019, 09:01   #7
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Re: Do Most Yanmars Have a Vibration Range Harmonic

If the vibration happens at a specific frequency range, it is a resonance issue. Resonance is a function of the mass that's vibrating and the stiffness of the mounting spring. In this case the mass (engine) is what it is. The spring is the mounts which are normally stiff enough so that the resonance frequency is much higher than your operating range. I would check your mounts.
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Old 07-09-2019, 09:05   #8
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Re: Do Most Yanmars Have a Vibration Range Harmonic

To answer your question no.

During the sea trial of our new to us Hunter 46 we experienced a similar vibration from our Yanmar. During haul out for an out of water survey discovered one of the 3 propeller blades had holes in it caused by corrosion. Replaced the 3 bladed propeller and the vibration went away.

Similar issue occured on my Spindrift Motor yacht with two Volvo Penta engines during its first trip up the coast from Los Angeles. Apparently one of motors was not aligned properly after new shafts were installed. After arriving in San Francisco the engine motor mounts were adjusted and the vibration want away.

Similar thing occurred on my waterski boat with a PMC marine engine. When I pulled the boat out of the water discovered a piece of submerged wood lodged itself on a fin ahead of the propeller which caused water to vortex around the propeller. Once I removed the wood the vibration went away.
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Old 07-09-2019, 11:08   #9
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Re: Do Most Yanmars Have a Vibration Range Harmonic

My Yanmar 3YM30 has no vibration and I also have a Max 2 blade feathering prop.
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Old 07-09-2019, 11:20   #10
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Do Most Yanmars Have a Vibration Range Harmonic

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Originally Posted by Shenandoah52 View Post
That wouldn't be the case because different rpms create different harmonics. A property known as 'resonant frequency' is inherent in all components and just as waves can build upon each other, or cancel each other out, the same can be said of your drive system.



If your Yanmars have no vibration at those rpms when the shaft is not spinning, (tranny in neutral) and occur only when the shaft is turning than you need to look at the shaft system, that being the shaft, bearings, couplers, prop, zincs, etc.



As silly as it sounds changing the shaft zinc may be all that is required to change the harmonics and get rid of the vibration in a best case scenario.


This, trust me from a 20 yr experience of maintaining helicopters. It the SYSTEM, not the individual parts that exhibit harmonic resonances, and identical aircraft due to slight differences can exhibit different harmonics, many things were done to discourage harmonics like odd gear ratios, components spinning at different RPMís etc. , but it still was occasionally an issue.
Even if the engine doesnít vibrate at X RPM or the drive train, itís entirely possible that the two of them do, but donít separately.

Itís common for example for an airplane that had a two blade prop for extended time to have a harmonic if a three blade prop is fitted, where it wouldnít if it was fitted from new, but no one, or none that I could find in Hartzell propellor or Avia Propellor or Lycoming engineís could explain either why or how, but Engineers from all three recognize the issue.
Sometimes the Science breaks down and you solve it by trial and error, or give up trying.

Really, honestly once you determine there is no fault like bad motor mounts and or shaft alignment etc, about all you can do is transition though ranges that exhibit harmonic resonance, do not operate in them. Excessive wear can and will result.

On edit it could be a bad / dirty injector causing what amount to a misfire. You just have to start eliminating things, and if you donít know when the injector were last cleaned they likely could use it anyhow.
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Old 07-09-2019, 11:21   #11
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Re: Do Most Yanmars Have a Vibration Range Harmonic

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Originally Posted by epoxyman View Post
I have a 4JH4E on a Cal 39 MK2. The engine runs smoothly from idle to 1800 rpm then vibrates wickedly until about 2300 rpm then is reasonably smooth to about 2600 rpm. I have a two bladed Maxprop feathering prop.
i have same engine with 3 blade FOF, it doesn't vibrate
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Old 07-09-2019, 11:27   #12
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Re: Do Most Yanmars Have a Vibration Range Harmonic

Harmonic resonance, in this case itís called ground resonance, but shows how destructive resonance can be.
https://youtu.be/0FeXjhUEXlc
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Old 07-09-2019, 11:42   #13
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Re: Do Most Yanmars Have a Vibration Range Harmonic

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Even if the engine doesnít vibrate at X RPM or the drive train, itís entirely possible that the two of them do, but donít separately.
Yes, what you said is indeed true. I alluded to that same phenom when I said, "A property known as 'resonant frequency' is inherent in all components and just as waves can build upon each other, or cancel each other out, the same can be said of your drive system."

And when I said, "If your Yanmars have no vibration at those rpms when the shaft is not spinning, (tranny in neutral) and occur only when the shaft is turning than you need to look at the shaft system,..." I was also alluding to the same phenom as your example where the engine ran fine until coupled to another component such as the props you mentioned. My suggestion being to look at the shaft system first.

We're basically on the same page here but I think you gave a good explanation that was probably better than mine.
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Old 07-09-2019, 12:30   #14
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Re: Do Most Yanmars Have a Vibration Range Harmonic

I have 4jh3e , Had a bent shaft and broken motor mount ,Didn't know it ,Increased rpm 500.
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Old 07-09-2019, 12:35   #15
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Re: Do Most Yanmars Have a Vibration Range Harmonic

We have had two boats with 4JH4TE engines. 730 hours on this one (saildrive)
We have never experienced a vibration. You donít have an engine issue, look elsewhere as others have suggested: engine mounts, cutlass bearing, prop, zinc.
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