Yanmar 3JH4W 40hp question

[letskeepriding]

so now that I've had a chance to use my new boat I have a question about the engine. 2005 40hp Yanmar. From idle to 1900 RPM it is not as smooth as I would expect. She shakes a bit. Not a huge amount, just not smooth. At 2000 RPM she smooths out and does not shake at all. I have no experience with these engines so I'm looking to find out if this is just how they are or if I should look into this further. In a former life I was an auto tech for 15 years so I have some mechanical experiance just not with diesels or this engine. Enough that I notice if things are not what I think they should be. The yard is so backed up I can't get anyone to even look at it for a few weeks. If anything I'm thinking a slightly clogged injector could cause this. I adjusted the valves over the winter and only one was slightly out of spec and the engine was clean as a whistle. If it were a compression issue or a balance issue it would not smooth out over 2000. The engine mounts appear to be ok as well. Not collapsed or torn. Before I go making work for myself I thought I'd check. thanks

 

[sail sfbay]

Same engine on my 2004 Hunter 386 did not vibrate. Vibration could be caused by a fouled or corroded propeller or unbalance motor mount (s) in my experience, which I have experienced both:

1. fouled propeller on my Sport Nautique from a piece of wood lodged on the propeller resolved by removing the wood piece after I trailed the boat out of the water
2. corroded propeller on my Hunter 46 resolved by replacing the propeller
3. misaligned shaft on a 56 ft Spindrift Motor Yacht after it went out of alignment on trip from LA to SF in heavy seas resolved by shimming motor

My 2 cents is inspect the propeller, and shaft alignment and have a Yanmar diesel engine mechanic inspect the engine and motor mounts.

 

[quadrille38]

Have same boat but a 2008. Same 40 hp engine too. Do not experience vibration you describe.
Id go with sf bays suggestions above.

 

[letskeepriding]

thanks guys. I'll check it out. I appreciate the help

 

[sail sfbay]

Plesse let the forum know what you learned and what the fix was so we can learn from your experience.

 

[letskeepriding]

Will do. Could be a while before anyone gets a chance to look at it.

 

[P12nash]

My 2007 does the same thing. I know there is a small amount of play in my cutlass bearing but a surveyor suggested this season that I should be able to get another year or two out of it. Not sure if that could have anything to do with it. I’d definitely be interested in what you hear back to see if it would have any impact on my vibration.

 

[splax]

soft foot condition motor mount causing slight misalignment....?

 

[letskeepriding]

so the consensus from the marina tech, a surveyor who was by to check some other things, and a guy on my dock who looks like Ernest Hemingway is that the mounts are soft. I did check the alignement and it was out only slightly. .005. The marina tech said that was not enough to cause this issue. So, I'll put some mounts in and see what happens. They had the two rear ones in stock so I'll start with those.

Apparently the metal parts of the mounts are made of "unobtainium". A precious metal used in most parts for boats, Ducati motorcycles and Ferrari's. This accounts for the "Are you F@#$ing kidding me" price of the mounts. Luckily I also own a Ducati and am well versed paying $189 for a $39 part. Otherwise I might be upset. Ernest choked on his beer when I told him.

I'll let you know how it works out

 

[sail sfbay]

Good ti hear!! Great progress!!