How much vibration in an outboard is normal?

[Stingrayzuke]

I know up front that this question is going to be difficult to answer, but I have a 2017 DF115A and I am curious if the amount of vibration and noise level I get is normal. There is definitely a shake to the motor at idle and I get resonance from the motor in the mid 3000rpm range, where the sound echos through the ski locker. And then various rpms there will be vibration sometimes that vibrates the windshield or whatever is in the cupholder. I was kind of thinking the motor would be quieter in general than it is. I am also having the issue with the top speed and top rpms so maybe the motor is just working harder than it should. It is in the shop now and am having them look at the vibration but I don't know if anything can be done about vibration even if it is more than normal.

[Moonlighter]

A very good chance that at least some of the vibration is due to the motor being too low and the engine “lugging” due to being under excessive load to to a combination of the engine too low and being overpropped. I suggest you wait until the dealer addresses the engine height, prop and now the vibration issue as per your other thread. Theres a possibility of course that there is a misfire, but they should detect that and fix it while it is there if thats the case.

If it was me, I would want them to confirm by their own own onwater test that the engine and prop are now working as they should be and that they motor can now hit 6000rpm at WOT, trimmed out. I would also ask to be shown what they changed, and to be told exactly what was done to address the problems.

That said, you will tend to hear resonance type vibrations from 4 strokes far more so than on 2 strokes - simply because they are so much quieter than 2 strokes that you can actuallly hear these things, where the noise and rattling of the 2 stroke drowned them out!

For example, on my own boat with DF115, at idle I can get a vibration from a strut that holds the hardtop roof up. But if I give it just a tiny touch more revs, it stops.

So you might have to do some searching on the boat to find the source of this kind of resonance, and maybe move things around in that ski locker, or adjust the hinges so it closes more firmly.

Id also add that 3000rpm on the 115 hp is often around the point of greatest engine load, as the motor is trying to push the boat over the hill onto the plane - boat can be half on and half off the plane at those revs. Try not to run it at those revs especially when new and still being run in, it is loading the motor up. So push it up a bit more to closer to 4000rpm. It will run easier and have less load on the emgine. Also, when they fix the engine height, it will help this as well.

But normally, when changing from 2 stroke to 4 stroke, the biggest dangers are restarting an engine that is already running, and forgetting to turn it off when pulling the boat out at the ramp - both scenarios being due to the engine idling so quietly you dont realise its running!

[Hoosmatroos]

Keep in mind that an unbalanced prop can cause huge vibrations. 2 months ago my prop is balanced and turn much smoother.

[Moonlighter]

Keep in mind that an unbalanced prop can cause huge vibrations. 2 months ago my prop is balanced and turn much smoother.

Yes, very true!

Even a new prop can easily be out of balance, which can be resolved by having the prop scanned and then tuned so that the pitch of all blades is matched perfectly and the prop balanced too.

[Greg Moore]

Agreed, start at the prop. Borrow one even if possible to compare. I have a DF140a on a pontoon, virtually identical motor. At an idle out of gear I don't know it's running back there. In gear it vibrates enough to rattle a couple of spots thru the boat but add even another 100rpm and tough to tell it's running again. Yes it gets louder as load increases but really I've never been on a pontoon boat with a quieter motor at any speed and at cruise of 25mph and about 4800rpm there's more water noise than motor noise