Not Terrible Cummins QSC8.3 Vibration

What would you do next? I've had a slight engine vibration over the last 6 months and can't seem to resolve. 2006 Twin engine boat (Fleming 55), engine hours around 4500. We have...1) Dove on props and running gear, had divers check props and running gear, had boat pulled and had mechanics and surveyor check props and running gear, tuned the propellors, had 1000 hours service performed, 2 fuel injectors replaced, ran oil tests on transmission, and engine, switched the balancing weight from one engine to the other (not sure what this was called) all performed by former direct Cummins mechanic. He also assessed engine mounts and following that sort of put up his hands.
Should I just leave it and cross my fingers? Anyone have a similar issue and found resolution?

Did you do an engine alignment? I have had that cause a vibration. We had Drive Savers on the engines when we bought the boat. Eventually I removed them and had a spacer made by Spurs to replace the Drive Savers. Then I was able to do an accurate engine alignment. Took care of the vibration.

Comodave said:

Did you do an engine alignment? I have had that cause a vibration. We had Drive Savers on the engines when we bought the boat. Eventually I removed them and had a spacer made by Spurs to replace the Drive Savers. Then I was able to do an accurate engine alignment. Took care of the vibration.

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We did not - However, this boat has the Aquadrive system which as I understand it, isolates the shaft from the engine allowing for softer mounts (minimizes normal engine noise/vibration) where precise alignment is not necessary.

What happened 6 months ago? Where is vessel located?

The question has so many potential answers especially given all the work that’s been done. Was damper plate checked? High pressure fuel pumps can cause vibration as an early sign. Were all injectors pulled and tested, more than just a visual?Aqua drives are not fail safe by the way.

Suggest you call or text Seaboard for suggestions.

Acquaintance had alignment done with no joy. Eventually shaft was removed and was slightly bent. Said bend so minor he couldn’t see it. Only aware of problem at high rev. Told story at dockside so don’t have further details. Sorry

FIRE said:

We did not - However, this boat has the Aquadrive system which as I understand it, isolates the shaft from the engine allowing for softer mounts (minimizes normal engine noise/vibration) where precise alignment is not necessary.

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Theoretically they should be good then. Ok. I am out of suggestions…

You say it is a slight engine vibration.

Does that mean if you were to run the engine in neutral at whatever RPM is most annoying while tied to the dock, the engine displays this vibration?
Or does it mean that the vibration is only evident when the boat is actually underway at whatever RPM and the vibration is readily evident if you feel and look at the engine?

If the later is the case is the vibration also evident on things like railings, or a flagstaff?

Run each engine individually under load and see if you can isolate to one side

sunchaser said:

What happened 6 months ago? Where is vessel located?

The question has so many potential answers especially given all the work that’s been done. Was damper plate checked? High pressure fuel pumps can cause vibration as an early sign. Were all injectors pulled and tested, more than just a visual?Aqua drives are not fail safe by the way.

Suggest you call or text Seaboard for suggestions.

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That's the funny thing - NOTHING really happened 6 months ago. The issue just sort of showed up one day when I noticed the flybridge helm chair's armrest seemed to be oscillating. I checked the engines and noticed the starboard side was noticeably but only slightly more shaky than port. At that point we were coming back from the Bahamas and after calling on all my resources decided to finish the trip back to MD (Kent Island) and have more extensive testing performed. Transmission was not separated form the engine so no one had access to the damper plate...but no noise is associated with the vibration I am experiencing. High pressure fuel pump...That I will have to check on. I have noticed that when I rev the starboard engine out of gear the engine seems to hiccup before smoothing out....
Fuel injectors were electronically assessed and two were marginally bad and replaced while the others check out.
Good call on reaching out to Tony/Seaboard

Crux said:

Run each engine individually under load and see if you can isolate to one side

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Yep - it is definitely the starboard engine!

There are professional vibration analysis techs out there that can determine the frequency and amplitude of the vibration. That can tell you if it’s from the propeller, shaft, or engine. For a simple example, you run at 2000 rpm with 2:1 transmission. Is the vibration at 2000/min, 1000/min, 4000/min?

luna said:

You say it is a slight engine vibration.

Does that mean if you were to run the engine in neutral at whatever RPM is most annoying while tied to the dock, the engine displays this vibration?
Or does it mean that the vibration is only evident when the boat is actually underway at whatever RPM and the vibration is readily evident if you feel and look at the engine?

If the later is the case is the vibration also evident on things like railings, or a flagstaff?

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Happens at the dock and underway - Some RPM's and some days the problem seems worse than others. Yes you can notice the vibration by feeling cold parts of the engine (I hold both and compare ones side to the other), oscillation of the air breather, flag staff, seat armrest etc.

High Wire said:

There are professional vibration analysis techs out there that can determine the frequency and amplitude of the vibration. That can tell you if it’s from the propeller, shaft, or engine. For a simple example, you run at 2000 rpm with 2:1 transmission. Is the vibration at 2000/min, 1000/min, 4000/min?

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Had no idea - How do I find one?

FIRE said:

Yep - it is definitely the starboard engine!

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I am assuming that you ran the starboard engine in neutral with the port engine off and still had the vibration. You then ran the port engine in neutral and the starboard engine off and there was no vibration. Is this correct?

The Aquadrive uses CV joints? They can wear and cause vibration.

If it occurs with the same amplitude at the dock and underway we can pretty well rule out the drivetrain and just concentrate on the engine or whatever is spinning in neutral.

If the engine is missing a firing stroke you would have thought the mechanic would identify that and fix it.
I have no idea what the "balancing weight" that the mechanic switched from one engine to the other is, but on the surface it sounds weird. Anybody know?
Is there an easily re and re'd balancing shaft on these engines?

If the 1000 hour service did not include setting the valve lash, I would do that, it's likely not hard to do.

I would then do a leak down test to see if all the cylinders are basically even. You likely don't have the tools, so have this done.

After that, there is likely a viewing port in the bell housing where if you open the port you can view a small portion of the torsional coupler and along with a remote starter or better yet, an assistant to slowly bar the engine over you can inspect the coupler.

With most other things eliminated I would then suspect the engine mounts.
Aquadrive says they use soft mounts as no thrust is applied to the engine. Soft mounts may wear out quicker.
If they are originals, at 18 years and 4500 hours, they are likely overdue for replacement.
Aquadrive no doubt charges a princely sum for their mounts which look awfully similar (if not the same as) Trelleborg's Cushyfloat mounts that I replaced on my ride 8 years ago at 20 years old and 3500 hours. Things noticeably smoothed out with the new mounts.
They were relatively economical back then.

Maybe get a mechanic’s stethoscope and move it around the engine and drive train and see if the vibration is more noticeable in one area. I have one and it was about $15. Might be worth a shot.

I went to google maps and typed in Vibration Analysis near me and three companies showed up within a 100 mile radius. I m used to industrial guys we had available that worked on multi million dollar machines but it might be worth a phone call. These guys could tell the difference between vibs caused by impeller vanes passing the pump casing from vibs made by the number of balls in a bearing. Plus how to solve the problem. Good luck.
PS one of our senior navy mechanics used to scoff at the above techs. He would lay a nickel on a suspect bearing. If it just laid there it was good. If the nickel “danced” it was bad.

FIRE said:

Happens at the dock and underway - Some RPM's and some days the problem seems worse than others. Yes you can notice the vibration by feeling cold parts of the engine (I hold both and compare ones side to the other), oscillation of the air breather, flag staff, seat armrest etc.

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So you can rev the engine up in neutral and you get the unusual vibration? If so, it's and engine-related issue, not a drive line issue.

Has the torsion coupler ever been replaced? At around 5000 hrs, I'd say it's a strong candidate.

Quote: luna
If they are originals, at 18 years and 4500 hours, they are likely overdue for replacement.
Aquadrive no doubt charges a princely sum for their mounts which look awfully similar (if not the same as) Trelleborg's Cushyfloat mounts that I replaced on my ride 8 years ago at 20 years old and 3500 hours.

They are most likely Cushyfloats by Trelleborg, take a look here:


Probably 17/1657 - durometer number, which is found on the base near the
Mounting hole. All Rubber mounts stop performing per specifications after 10 years of service. Doesn't mean they stop working, they are just tired.

And even though your mechanic checked them, a simple check is to seee if they have settled uniformly, the A dimension in the attached should be within a mm or 2 front to back, Start with the mount under the injection pump, they typically fail first from contamination.

Not to say this is your problem, but it is something you can check and consider.

One last comment, Aquadrive has a specific window of misalignment that's the sweet spot for those units. I believe 3* was the magic number. Can be = or -, but not zero. So you just can't change the mounts and not do an alignment.

Here in Ft Lauderdale there a a bunch of vibration specialists, and they can pinpoint a vibration with accelerometers and graphs. Firing rate, rotation, gear mesh, shaft rate, prop rate will all show up, the spike will be the culprit