How much does your outboard engine vibrate?

[Regular Guy]

I would like to hear what your experience is regarding vibration from your outboard engine.
I have bought a new Honda 9.9 hp outboard engine, xl shaft drive. The break-in procedure by manual is 10 hours. I am in the 6th hour now and can go 80% of throttle but not more than 5 minutes at the time full throttle.

However, I discovered a strong vibration; the swim ladder on the transom for example is rattling, also it become very noisy in the cabin already by 50% throttle. I have not had that with my old 8 hp Mercury 2-stroke.
I had the new engine checked out by two different, independent Honda service stations and both told me nothing is wrong with the engine. The fact is, the vibration is there; and I’m concerned it may harm the boat; the rattle could crack the joint between the bottom and deck part on the transom or who knows what else.

Am I too concerned, will the vibrations go away after some more hours? What do you think? Thanks,
Hart

 

[rufus1138]

haha, this is good, the service techs are right, its going to vibrate, dont worry too much. my h27t has a honda 15 on it and the whole hull hums when you are running under power. my 33 has a yanmar 2gm20 raw water 2 cyl diesel and you can litteraly see rings coming off the hull when its idling at the dock.....bang bang bang they go, if you want to avoid the vibrations id go back to the 2 stroke, i wanted to on the 27 really really badly. but then again i live aboard so moving to the 33 was more important.

 

[Chief RA]

You might want to see if you can take it back under warranty. I just bought a 9.8 Tohatsu and do not have a vibration problem. I'm would think it is less expensive also. The fact that it is a 4 stroke shouldn't cause excess vibration. Chief

 

[Chief RA]

I just mentioned this problem to my wife. She was parts manager for a Yamaha dealership for years and she says it sounds like you either have a bent prop or bent driveshaft. Remove the prop and see if the vibration continues. You might want to take it back to the dealer and refuse to accept it back. Make them replace it with another one! Chief

 

[seadaddler]

2 stroke 4 stroke

I have heard 1 or 2 times the different way a 2 stroke runs
compared to a 4 stroke but I have a 2 stroke and just throw it in the mix.
nick

 

[twodzusfittings]

I have vibration and I think I know why. Before installing the new Nissan (Tohatsu) 9.8 I removed the engine mount and put a 12 x 12 aluminum plate on the outside as well as the inside, sandwiching the transom. What I neglected to do was to put in a 1/8 inch piece of neopreen of equal size as a dampening agent. I re installed the motor mount and then installed the motor. This was suggested to me by a friend, after the fact. So this year i will put up with the noise and when redo every thing this winter. After the noisy two stroker, this is not so bad.

 

[CharlzO]

I would say in the meantime, see if you can find a dampening agent of some sort to clamp onto, even some simple foam gasket something or other might help at least a little.

 

[Benny17441]

No I would not think the vibration is going to go away by itself. It is somewhat normal for engines to vibrate some at certain RPM points but not throughout the entire RPM range. I would suspect a out of balance prop. Like Chief suggests remove the prop and run the engine to see if the vibration diminishes. If it remains then I would look at the engine dampers where the cylinders block attach to the casing. Last I would consider the boat's motor mount; see if you can improve the dampening.

 

[Crazy Dave Condon]

Hart;

That is a four stroke engine and will vibrate a little more than a two stroke. Nature of the beast. However, check the tightness of the bolts of the motor bracket where the bracket attaches to the steel supports and also to the transom. If tight, you will have to live with it. Nothing wrong. Maybe you might want to tie a line between the steel brackets tight and see if that might dampen that noise. Just a thought sir. If it works, then you with an engineering background then can come up with something. Again, just a thought here. Take care.

Poor old Kermit had to put up with me for two days but I gotta say he is a perfect host.

 

[isaksp00]

My 8HP Honda does send a fair amount of vibration into the hull at certain RPMs. I don't get any undue vibration when I run it off season in a can of water - that is, it is not the motor itself that is making the noise. Must be harmonics where the vibration frequency of the motor just matches the hull or other part natural frequencies.

If you can run it off the boat easily in water, and there is no vibration then, I'd assume it is just the hull harmonics.

 

[BrianW]

Not Much Vibration on Mine!

I have a Honda 9.9 on my H26. The transoms are different on our boats, but I have very little vibration at 3/4 throttle. It is also very quiet! Prior to the Honda, I had a Johnson 9.9 two-cycle. BrianW

 

[Chief RA]

Vibration problems have little to do with whether the motors are 4 stroke or 2 stroke. It is more related to the size/style engine you are using. Most outboards change from a single piston to twin piston at about 6 hp. Of course the twins are much smoother than the singles. Chief, past Yamaha dealer

 

[twodzusfittings]

After reporting on how my motor vibrates the other day and my solution steps to be taken, I found a temporary solution while out on the water yesterday.
I noticed that when I put down pressure on my tiller, the noise level would drop. So I filled a wash bucket with water and roped it to the tiller. I had a peaceful trip back up the river. I will still keep my original solution on the to do list, but in the mean time this will work for me!

[/IMG]

 

[Crazy Dave Condon]

Chief;

I can only report what I saw over the past 45 years as well as what others say about 4 vs 2 stroke harmonics. The tiller I forgot about that. However, we all can agree is can be nerving to listen to the rattling noises.

 

[Regular Guy]

Thank you for all your contributions. I can't hide how disappointed I am with my new Honda 9.9 hp in that regard.
It does vibrations at any rpm, so not really a harmonic match of frequency wave lengths. Also when put in neutral (shouldn't that be doing the same as taking the prop off?) the same thing. Means no shaft or prop issue.

They won't take the motor back since nothing wrong with it was found.

I will try a dampening agent, starting with some old line under the clamps as Uncle Crazy Dave suggested. Have to look for something permanently when that reduces the rattle.

Thank again for all that great input, I feel not to be alone with that problem.

Kermit and Crazy Dave: Wishing you both good times ....
Hart

 

[Chief RA]

Read the warranty carefully as I would think that if you can't abide the vibrations they have to take it back. I had a dealer tell me he wouldn't give me my money back on a new faulty inflatable and I got him to take it and check it out. I then called the Visa card company and explained the dissatisfaction with the boat and they cancelled the payment quantity to him. Chief

 

[Ward H]

Interesting solution. I have some hatch lids that rattle and buzz at certain RPMs unless someone is sitting on them.
My 9.9 Yamaha vibrates a bit at idle but smooths out at higher RPMs.
I do notice more noise and vibration when the boat gets to hull speed and I try to push it harder.
You mentioned 80% throttle. My O'day has a displacement weight of around 4,000 lbs. I never need to exceed 50% throttle, even when heading into heavy winds and 3ft chop.

If I'm motoring more than the 10 mins needed to get the open, I watch my speed on the GPS. Once I get to what appears to be max speed, I throttle back until the speed just starts to drop off.

Last week I was motoring into 18 to 20 winds just off the bow. I wanted to extend my fuel range so once I hit 5.8 kts I backed off the throttle until I was at about 5.6 kts so I knew I was not applying more throttle than needed. Throttle was about 45%.
Anymore throttle than that was wasted power and fuel as well as more vibration and noise.

 

[Happy Daze]

can you post a picture of how your auto tiller is mounted to the boat? I do not want to connect mine to the lifting seat cover.
Thanks

 

[pacerpilot]

Your engine is probably ok. What is more than likely happening is the transom is "drumming". Think of the transom as a drum head and the engine as the stick. The thin fiberglass actually increases the vibe. Different speeds cause more or less vibe. However, Chiefs right, check the shaft by removing the prop. It only takes a minute to be sure.

To dampen the vibe, install a plywood doubler inside and out on the transom. The plywood will stop the vibration and help support the engine.

I've run an old Honda 9.9 on my previous boats and found them very quiet, smooth and, fuel efficient. I wish I could afford one again. My 1968 Evinrude 6hp will have to push the Mac for now.

 

[Crazy Dave Condon]

One thing to remember. Use straight gas and not oil mix in the gas with a four stroke engine. Even better, find places that sell gas without ethanol or what I call corn crap in the gas. I have heard of that causing an engine to run rough.