Terrible Vibration with New 4 Stroke Engine

[edbuchanan]

Hi All,

I just bought a new Tohatsu 6HP 25" 4 stroke outboard to replace my ancient 2 stroke Johnson.  To get to the point: when the Tohatsu is put in gear, there is a violent shaking, even at low RPMs.  The vibration does not change much as the speed changes.  No reasonable amount of steering friction would keep it straight.  It was also quite shaky in tests on a saw horse with the lower end in a barrel of water.  Out of gear the motor is very quiet and smooth.

The engine was bought on internet; it showed no damage to the styrofoam packaging around the lower end.  It looks quite perfect.

The Tohatsu dealer thinks it might be a problem with the mounting on the boat.  The example given was a soft spot on the transom or loose clamps on the motor.  I have the original 2 stroke Garelick on the boat.

I called Com-Pac to inquire about a mount.  He had never heard of such a problem.  He also said that Tohatsus very rarely have problems.

I noticed that Garelick mounts intended for 4 stroke engines are quite a bit wider than the old 2 stroke variety.  This is most likely to prevent "harmonic vibration".  I will purchase one but somehow I don't think it will fix the problem.  Suggestions?

Ernie


   

[mattman]

If only in gear, prop balance or a shaft out of alignment. Maybe the prop blades have been bent or one blade is out of pitch...never heard of this in an outboard, but vibrations from a misaligned inboard, fouled prop or worn cutlass are not uncommon. I don't believe it is the motor mount. Interested in others opinions. btw when I got my new 3.5 she ran pretty rough the first hour or so, lower unit was tight and it took time to loosen up to run in gear at idle. after that no problems. best of luck.

[MacGyver]

Ernie,

I too have the same engine and am surprised by the vibration..... to be honest I thought maybe it was a problem till I talked with a mechanic just the other day. He says they run like that..... and only the in gear is a issue for me as well!

I get a vibration through the boat sometimes making it sound as if the boat will come apart, but no issues.... and I cant see any problem with the mount either and I have seen and dealt with boats a long time with it being my job.

I thought this year I would take a video of it and post it to see what others have on here. The only thing that is a little different from what I have is when you say of tightening the turn screw, I too have the issue, and cant seem to get it tight enough, but saw somewhere that it is a normal problem on them as far as tightening that thing down.... I plan to look at that when I get it home from storage.

At any rate, maybe someone else like Billy, or someone can spread a little light on the subject as far as their experience as well. It is a fantastic motor, and I really am impressed with the performance, but the vibration at times is pretty unlike my old 2 stroke......... makes me yearn for a old twin engine, atleast they balanced well...

OH, I have a CP19.

Mac

[edbuchanan]

Thanks for the replies.

Mattman: yes, that is my suspicion, I will check the run out for the sake of my mental health.

MacGyver: which motor mount are you using?  It is possible that a proper 4 stroke mount might fix the problem.  The 4 stroke mounts are much wider than the 2 stroke types.  This would probably prevent some wiggling.

[MacGyver]

My mount is a SS style, and i installed a new plastic motor mount board. I dont remember any wobblyness in the mount, but that isnt saying much..... I havent been messing about with the engine stuff since last year.

I do know of smaller mounts than the one I have, and I could see those making noise and such, but mine is now spaced out farther with the addition of HDPE blocks, and a giant aluminum plate on the backside. One thing to note is on the old engine, I didnt have those additions, so maybe some of my issue is too rigid of a connection to the boat that it easily transfers the sound through the boat......

In this link I have a bunch of pictures, and this page I linked to shows the motor mount a few times. See if it looks like yours or not.

http://cpyoa.geekworkshosting.com/forum/index.php?topic=6212.75

Mac

[skip1930]

Every engine has a harmonic vibration somewhere with-in its useable rpm.
So as the rpms change the vibration should change.
If the vibration occurs on the motor mount and off the motor mount, at all rpm's start looking at ...

Look at the prop. Look for a bent output shaft, the 90 degree prop drive, bad bearings, bent crank shaft, fouled plugs if it's 2 cylinders.
Pull the prop off and run it. Adjust the valves on this 4 stroke. Check the timing. Check the water pump and everything else that moves rotationally.

If nothing fixes it, throw it out.

skip.

[edbuchanan]

Hi MacGyver,

Your motor mount looks pretty beefy.  Mine is the old fashioned, quite narrow type.  I was hoping you would also have the narrow type as a possible explanation of the vibration.  Oh well.

[edbuchanan]

Here is a video of a Tohatsu 6HP running while mounted directly to a transom:

http://www.youtube.com/watch?v=spSDFCSIaO8

Note that there is no vibration on the motor or the skipper's hand.

[HideAway]

A friend of mine bought a new Tohatsu 6HP 4 stroke and while I did not run it I was surprised how noisy and how much vibration it had under load and at idle compared to my old 8hp Evinrude 2 stroke.   We were motoring side by side in calm water at the time.   I thought that it may be caused by the single cylinder vs the twin cylinder Evinrude or some other engine problem.  A bent prop will certainly cause a vibration but it feels different than an engine problem-  try to determine if it feel like the bottom end is shaking or the engine - I know that sounds weird but my experiences with out boards generally are

[atrometer]

You need to take it to a GOOD Tohatsu dealer (warranty).  I had one and it might have vibrated a teeny bit more than a 2 cyl, but I was surprised how well balanced and smooth it was.  You Definitely have something wrong!  Watch the video, that's how it should be! 

[MacGyver]

Actually, I wonder if it is the mount now, because in that vid I can see the warble on the sleeve and such which shows the transmission of vibration is actually being picked up by the camera. Also his engien sounded exactly like mine, so I am pretty sure that mine at least might be right as it should.

Your smaller footed mount could actually be a issue, and I have seen those mounts and worked on mounts similar to it that caused issues like you describe.

The mechanic I know says the Tohatsus and other ones like it will vibrate, it is just the nature of the beast.

Mac

[MacGyver]

Look at this video, same guy, but watch the handle, itll show the shake from the first that it still does, it is just since he is part of the boat he is with the vibration.... if that made sense....... I need to go to bed, i am tired....

https://www.youtube.com/watch?v=mod-wNvTC1I

Mac

[Jon898]

This may seem like a dumb suggestion, but you may want to be sure the lower end is lubed.  Sometimes engines are shipped "dry", and it's easy to fill up the motor oil and forget the lower end.

[brackish]

I have that motor.  While it certainly has more vibration than the two cylinder 9.9 four stroke Suzuki it replaced, I was expecting that to be the case because of the single cylinder.  It is about the same as the Utube video posted above and it does not change if it is put in gear, the level of vibration remains the same. 

I have a very substantial mount, and I normally use the mount position that is second from the bottom.  The motor pin position puts it almost perfectly plumb with the world when at rest.

To Skip's point, there is a zone from about 1800 to 2000 RPMs that it doesn't seem to like.  Vibrates slightly more in that range which causes the motor cover to rattle.  Past that zone, lower or higher,no problem

[edbuchanan]

Jon898: thanks, but I did check the gearcase oil level before starting it the first time.

brackish: mine vibrates at all speeds.  This weekend I will check the runout of the propellor and output shaft.

MacGyver: I will tighten the bolts on the mount to see if there is any perceivable difference in the vibration.