Yanmar vibration below 1000 rpm - typical ?

skyflyer

skyflyer

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New (to me) boat and first one I have had with a Yanmar (3GM30F). Mounts have been changed and then had the shaft re-aaligned professionally; above 1000 rpm she's sweet as the proverbial nut.

Below 1000 rpm its a different story, lots of vibration and shuddering

It doesn't mater if in gear or not.

The taco is calibrated correectly so i know the rpm reading is accurate

Is this typical of the marque? if not, what might be the issue?

Many thanks
 
YES , recent discussion with a marine engineer friend ; how do those mounts look , ok, they are original (28 years) I'm asking because this engine bounces all over on tickover , aye they do that hop pity bouncy all over t place tha needs t push um they likes that.

John
 
New Mounts!! Professionally Fitted!! Have the correct mounts been fitted? Installed in the correct layout?

I had a similar problem a few years ago with a Yanmar JH2-E fitted in a Nautical 39. Before my ownership a previous owner had had the original mounts professionally replaced. The wrong type had been fitted, they were "softer" than the Yanmar spec for the engine.

Check what the ID mark is on each mount and compare this your engine spec. Be aware that some Yanmar engines have different mounts fitted on the Port and Starboard sides of the engine. My 4JH2-E does.

Have a look at this page on the Yanmar Help site for some background reading. http://www.yanmarhelp.com/i_mounts.htm
 
Schuss39 said:
New Mounts!! Professionally Fitted!! Have the correct mounts been fitted? Installed in the correct layout?

I had a similar problem a few years ago with a Yanmar JH2-E fitted in a Nautical 39. Before my ownership a previous owner had had the original mounts professionally replaced. The wrong type had been fitted, they were "softer" than the Yanmar spec for the engine.

Check what the ID mark is on each mount and compare this your engine spec. Be aware that some Yanmar engines have different mounts fitted on the Port and Starboard sides of the engine. My 4JH2-E does.

Have a look at this page on the Yanmar Help site for some background reading. http://www.yanmarhelp.com/i_mounts.htm
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Read my post more carefully - new mounts fitted, professionally aligned! I fitted the mounts myself, they are the correct one's in the correct configuration!

(I also started to do the alignment, but gave up in frustration - a classic example of a job that takes forever if you do it once but takes a lot-less when you do it regularly as part of your job!)


Edited to add : the graph and accompanying text in the link you gave indicates that vibration will increase significantly below idling rpm.
 
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Spyro said:
With a 3 cylinder I would have thought it should be pretty smooth. My 2 cylinder version is.
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Our 3GM30 is not that smooth under 900RPM, but fine otherwise while motoring at more normal revs. I have no idea of the vintage of the rubber mounts, but they look decent and nothing is detached/loose?
 
pagoda said:
Our 3GM30 is not that smooth under 900RPM, but fine otherwise while motoring at more normal revs. I have no idea of the vintage of the rubber mounts, but they look decent and nothing is detached/loose?
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Just put new rubber mounts on my 3 cyl Perkins, at tickover of 1000 revs it vibrates very slightly, at all higher revs its rock solid. with the old mounts, it jumped about at revs under 1000.
 
A 3 cyl. engine should be fairly smooth at the correct tickover speed. Are you sure that the mounts are sharing the engine weight equally both sides?
If the support nut on one has backed off unnoticed, this could cause the problem.
 
Have you checked that no parts of the engine are making contact with the engine bearers as the vibration amplitude increases when the revs drop.
 
KAM said:
Have you checked that no parts of the engine are making contact with the engine bearers as the vibration amplitude increases when the revs drop.
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+1 when I installed my new mounts last week, I found that one of the old adjusting studs was touching the alternator, when I installed the new ones I found it impossible to get the engine alignment without an acceptable clearance between the new stud and the alternator again.
I put a shorter fan belt on, which cured that problem.
 
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