Do Most Yanmars Have a Vibration Range Harmonic

[a64pilot]

Originally Posted by Shenandoah52

We're basically on the same page here but I think you gave a good explanation that was probably better than mine.

I don’t think so, your explanation was fine, I was just trying to agree with you was all.
I think we are right

[Q Xopa]

Originally Posted by Shenandoah52

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.

Yes, also being in the helicopter maintenance game I agree with the above explanations. With any power pulses, such as from a diesel engine, acting through prop blades against the water resistance. In between, or even just connected, we've got a bunch of items that flex at different rates depending on how rigid or flexible they are. Commonly prop shafts bent or misaligned, eng mounts, or anything loose. Like tuning forks. But change the rigidity or frequency (rpm) and that changes.

Long explanations aside, its usually something loose, or soft. Which is what has been said above. Its not always obvious, so the trick can be to find it.

Prop blade holes were mentioned above. These will give a lower frequency vibration than for example engine mounts. As in every time the offending prop blade goes past a loose spot.

The prop will cause a 1 per rev vibration.

The mounts, or anything not prop related, will give a 2 or 3 (depending on number of prop blades), per rev vibration. As in every time each of the prop blades go past the loose spot.

How does this help, well assuming you dont have vibration testing gear, you may be able to tell if its slow at the same speed as the engine, or if its 'buzzing' more.

But I start by looking, and tugging any usual suspects to feel for play etc.

[dennismenace111]

My 2Gm20F vibrates similarly. I've got a 2 blades prop. My sweet spot is around 2500 rpm where there is no vibration!

I know my mounts are a bit soft and I'm guessing I have some biologicals on my prop! Due for bailout in October when the weather cool s a bit from 95 to 93 so I can do the work my self!

[molly1]

I had a severe vibration at 2200 rpm in my Yanmar 4j but after straightening the prop shaft that was bent in one plane only (2mm) and putting on new zincs and prop speeding the prop It hums like a sewing machine though the whole rev range.

[dennismenace111]

Originally Posted by molly1

I had a severe vibration at 2200 rpm in my Yanmar 4j but after straightening the prop shaft that was bent in one plane only (2mm) and putting on new zincs and prop speeding the prop It hums like a sewing machine though the whole rev range.

I see $$ leaving my bank account at the next haul out! Here I thought it would only be a bottom job!

[ramblinrod]

Step 1. Inspect drive train for problem (/eg crab pot
Line around prop/shaft.

Step 2. Perform engine maintenance in accordance wit manufacturers recommendations. ((When was the last time valve clearance was adjusted?)

Step 3. Motor mounts are god for 5 years or 500 Hours. When were they last replaced?

[Q Xopa]

Originally Posted by ramblinrod

Step 1. Inspect drive train for problem (/eg crab pot
Line around prop/shaft.

Step 2. Perform engine maintenance in accordance wit manufacturers recommendations. ((When was the last time valve clearance was adjusted?)

Step 3. Motor mounts are god for 5 years or 500 Hours. When were they last replaced?

If you can check the manual for your particular engine. Not that it probably matters much in practise but Mr Yanmar recommends 4 years or 1,000 hrs in my 4JH4 Manual.

[Wotname]

Originally Posted by dennismenace111

My 2Gm20F vibrates similarly. I've got a 2 blades prop. My sweet spot is around 2500 rpm where there is no vibration!
.......

Another data point - from new, my 2GM20 ran smoothly across the entire rev range except at 2500 rpm where is developed a significant vibration. I always ran below 2350 or above 2650 without any problems!

I remember the Yanmar's operator's handbook mentioning the possibility of resonance at different rpm dependant on installation so I never worried about it.

I do think however, the OP's situation does sound serious and is worth investigating.

[skipperpete]

Originally Posted by epoxyman

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

Hi epoxyman
I think all Diesel engines suffer to some extent from this problem and the early version of your 4JH4 actually had contra rotating balance shafts in the lower crankcase to smooth out the vibes but that model was too heavy and too deep below the crankshaft for yachts so it was dis continued and later model engines came with the very soft and lively engine mounts you have now .
Very large marine diesels have a "critical range" or "Barred range" which shows as red sectors on the rpm indicator and can only pass through but not operate in the red.
Finally, if the engine alignment is good and the shaft is ok but the vibration is still happening .... consider that the load is not equally shared by the 4 mounts. It's not easy to adjust them all to carry the same load and if just one is too high or low the engine will tend to rock diagonally on the beds.

[Captain Bill]

Oddly enough I have the same issue on my 3jh3ce with sd60 saildrives. I never had this problem with my sd40 saildrives. I have a friend who replaced his sd50s with SD60s and now has the same problem. How could this be? Well I've been doing some research and found that not only is the saildrive replaced when the SD60 is installed, but the damper is also replaced and the technology used in the damper was changed as well. Yanmar changed from an elastomeric damper to a spring based damper. In the comments in the installation manual it says that this damper is now standardized across their entire line. I don't know if that means that you have the same damper I do, but the symptoms are the same. I suspect but cannot prove that this is the source of the problem.

I am on my second spring type damper and it is no different than the first. I had my props serviced and balanced and that made no change. I even had both transmission sections changed out for a different issue and still no change. I even had the prop shafts checked at a machine shop for bends and roundness and they were true to less than .001 inches. Bearing play etc. all in spec. I suppose it could be something in the vertical gear stack, but everything but the vertical shaft has been replaced with no change. I also had the engine mounts replaced and it is exactly the same on both engines.

[epoxyman]

Well Gents, You have all given some very interesting input. I will share some additional information as I have thought long and hard regarding your responses. When I purchased the boat (2017 late Fall) my first experience with the boat was the 2018 season. The boat seemed underpowered (which is ridiculous since this is a 55Hp on a 18,000 lb sailboat). So over the winter 2018-2019 I discovered that the PO had set the MaxProp 2 blade classic to the wrong pitch (feathering props have 3 designators not the normal 2) and the prop was severely under pitched (9 Vs 16 inches). So this spring I re-set the prop. The cutlass bearing was tight without wobble. I did put a heavy duty zinc on the shaft. Engine has 700 hours on it (installed in 2007). Engine runs beautifully, very smooth. At rpms of 1100 to 1800 there is little evidence of vibration and the boat speed is ~ 5.5 kts. Vibration is significant from 1800 to 2200 and above 2200 rpm the vibration is much less and the speed goes to ~6.4 kts at 2300 rpm. The engine is rated to 3000 rpm which I can obtain so I do not believe that the prop is over pitched. At 2600 rpm I attain hull speed of about 7.5 kts.
I have read that it is not good for the engine to run at low or at a single rpm for long periods of time so I run 2 hrs at 1750 rpm followed by 1 hr at 2400 rpm during long passages. I agree that the vibration is not normal (this is my 8th cruising sailboat), but this idea of resonant frequency harmonics has me puzzled. The response that the early model 4JH4E had known vibration issues and had dampening that was removed due to weight is very interesting and the input of the vibration pads(motor mounts) is also interesting. I would believe that the mounts have not been changed since installed. Does anyone know how to check the motor mounts for "softness" - is this a durometer test??? and also how difficult is it to change out the motor mounts??
Thank you all

[Compass790]

I don't believe it's not ok to run a diesel at the same revs for a long period of time. Many generators operate for 1000's of hours under those conditions.
Many engine manufacturers warn against running unloaded or just idling for long periods of time. Some yanmar manuals say to give them a burst of full throttle every so often tho. I suspect that's at least partly to stop exhausts clogging which they are prone to do in the crappy cast-iron elbows
Changing the mounts can be difficult just for access reasons but otherwise no biggie. Engine has to be aligned after. Plenty of you tube vids on that.

[skipperpete]

Originally Posted by Compass790

I don't believe it's not ok to run a diesel at the same revs for a long period of time. Many generators operate for 1000's of hours under those conditions.
Many engine manufacturers warn against running unloaded or just idling for long periods of time. Some yanmar manuals say to give them a burst of full throttle every so often tho. I suspect that's at least partly to stop exhausts clogging which they are prone to do in the crappy cast-iron elbows
Changing the mounts can be difficult just for access reasons but otherwise no biggie. Engine has to be aligned after. Plenty of you tube vids on that.

I agree compass790. Ac generators seem to live a long life with absolutely no warm up period and only the slightest variation of rpm at either 1,500 4pole or 3,000 2pole. They stay on speed/frequency continuously between oil and filter changes....... but I have seen the Yanmar instruction regarding continuous operation and varying the rpm so I do as they say.
On the idling issue..... I live part of the year in Asia and almost every diesel powered bus , minibus and RV is left to idle to keep the aircon functioning, often for hours but I have no idea how that affects their diesel engine apart from the fact that a lot have very smoky exhausts when underway( black smoke).

[hpeer]

I have the 4JH4-TE, it had 672 hours when we purchased the boat. And itnhad a vibration similar to what you mention.

I have:
Replaced the shaft
Replaced the prop with new
Installed a prop saver coupling
Had the engine aligned

Nothing made a significant difference.

In my case I think it is because we have a 7’ long 1-1/4” shaft. It is supported near the prop and then about 2’ behind the engine. So almost 5’ unsupported.

I think that distance is a bit much. My guess.

We generally run 1,700-1,800 RPM with the suggested bursts higher, although I didn’t do that at first. I’ve never seen any carbon build up. We now have about 2,200 hours in the engine.

[a64pilot]

If your engine is getting to full operating temp your not going to hurt to by running it slow.
Now understand a Diesel heats up based on load, it may not heat up at 2000 RPM in neutral but will at 1500 pushing the boat.
As has been stated your not going to hurt it keeping it at one RPM, after it’s been broken in.
Generators as has been stated blow a lot of myths out of the water, and yet low RPM generators are among the longest lasting Diesels there are, and they are not special generator motors either.

If you change mounts, I recommend doing so one at a time, using a 2x4 or whatever will fit to lever the motor up enough. Then measure the old mount and adjust the new one to the same, you will get very close that way.
Of course when removing don’t move the lower nut.

My engine mounts were about 29 yrs old when I changed them and gave no problem, and seemed fine, so I believe they will last longer than four years myself. I’m pretty sure they were original as they had the Yanmar grey paint on them and new mounts don’t come painted.
I need to get around to changing those 32 yr old hoses on the engine.