Yanmar 2G Engine Runs very rough under "load"

[Skippie10]

I have a Yanmar 2G Diesel (1985 year) in my S2 9.2 sailboat and it has operated without problems for 30 years (we have a 3 month sailing season).

Over the past several years, this engine seems to have developed a problem. The problem occurs when I put it in gear vs when I'm in neutral. When I go from idle and increase the throttle (when in gear), the motor shakes like crazy (I mean to say, it shakes the whole boat as if it is coming off of it's mounts!) It does not shake when I run up from idle in neutral.

At first, I blamed the folding prop but that doesn't seem like it would be a problem since the prop is geared so that both blades need to come "out" equally. And, I notice that if I increase throttle speed very slowly, it will go up in rpm without excessive vibration. Or, if it vibrates and I change the rpm a bit, it seems to "smooth out" and the vibration - eventually - disappears.

What to do? Someone suggested that my idle speed is set too low. Can it be as simple as that?

Don Voigt, Port Washington, WI

 

[woodster]

when is the last time you changed your mixing elbow

 

[Allan12210]

So, the problem appears when under load (i.e., in gear)? If the idle speed was too low it could shake and rattle when put in gear, but that would smooth out as rpm increases, so its probably not that. Does it act the same way when in gear in reverse as well as forward? I'm leaning towards worn or broken motor mounts as a simple cause. If the motor was constricted by too tight packing gland (acting as a brake) or a clogged mixing elbow, I would think it would make black smoke as well. Just as a double check, look at the air intake filter element and make sure it hasn't collapsed. Check the prop and make sure one blade isn't bent throwing off balance.

 

[Skippie10]

Mixing elbow?

when is the last time you changed your mixing elbow

Hi Woodster,

I'm embarrassed to say I don't know where the mixing elbow is....is that on the fuel line coming into the engine?

I can look it up - my manuals are all on the boat in the harbor.....Is that something that a person orders in advance and then installs when it gets here?

Don

 

[Benny17441]

A slow developing problem on a 30 year old engine; I'm afraid you will need a mechanic as it would be almost impossible to diagnose online. It could be one of too many things or a combination of them. If it was me I would start with the motor mounts; the might look new but they could very well be shot. It is hard for a small engine to shake the boat if it has new motor mounts. The next thing I would try would be remove, clean and balance the prop. Then would come engine performance, adjust valve lash, clean mixing elbow, replace all filters and make sure fuel is fresh. If all fails then you would have to look at cylinders compression, fuel injectors and governor operation. It does not end there but the best indicators perhaps are 1) is the engine smoking and what color? 2) is it quick to start or do you have to crank at it? These Yanmar engines do not take kindly to prolonged low speed idle and should be ran at 85-90% of maximum rate RPM. You may want to add a fuel additive to keep the fuel in the tank and the injectors clean.

 

[Maine Sail]

From the description...

The problem occurs when I put it in gear vs when I'm in neutral. When I go from idle and increase the throttle (when in gear), the motor shakes like crazy (I mean to say, it shakes the whole boat as if it is coming off of it's mounts!) It does not shake when I run up from idle in neutral.

Most Likely:

Alignment
Motor Mounts
Cutlass Bearing
Prop
Bent Shaft

Least Likely:

Engine Tuning Issues
Exhaust Elbow

 

[woodster]

Hi Woodster,

I'm embarrassed to say I don't know where the mixing elbow is....is that on the fuel line coming into the engine?

I can look it up - my manuals are all on the boat in the harbor.....Is that something that a person orders in advance and then installs when it gets here?

Don

the mixing elbow is at the end of the exhaust manifold and has a large hose coming out of it to the water lift muffler....it is usually a hump that goes up and back down

 

[Skippie10]

All excellent feedback. Now that I'm recalling the history of this engine, at one time - about a year ago, the intake air filter (foam) became weak and was - literally - sucked into the engine! At first, I worried about that but when I started the engine, it worked...so, I didn't give it much additional thought, at the time. Maybe that would foul things up, a bit....surely the mixing elbow would be a major area to look! I'll report back as to what I find.

 

[woodster]

follow main sails advice first ...he is the sherlock holmes of trouble shooting after you exhaust his recommendations you will well knowledgeable like you never thought you could be ......

 

[Benny17441]

No the foam filter would not be the cause. It probably evaporated soon after. I cannot stress the motor mounts well enough. They restrain the engine from vibrations and that fact that your engine is shaking the boat shows that at best they are worn and there is a possibility one or more could be broken. What usually happens is that the rubber separates from the metal bracket or split down the middle leaving just the weight of the engine to hold it in place. It could be some other cause for the vibrations but the mounts are not helping at all. When installing new mounts you need to realign the engine.

 

[Skippie10]

Wow, I get it! I'll check the mounts. If they do not look like they are cracked, is there a way to tell if they are good or bad?

I have an S2 sailboat (no longer made nor are there likely to be parts around). Where does a person buy motor mounts?

I have also contacted a boat/motor technician to have the shaft aligned and so I'll get the motor mounts, as well, and then have him align.

Don/Skippie of BVI

 

[woodster]

try here http://www.marinedieseldirect.com/c...l=2GM20F&manufacturer=Yanmar&catalog=Y00F5052

shop every one that will sell to you they have protected zones you need to know witch type you have

 

[Johnb]

The good news is mounts are available, through Yanmar or elsewhere. You should do some research to make sure you are getting the right ones, don't just replace with same.

The attached picture shows a mount that has bulged one side and needed to be replaced although it was not split or cracked.

 

[Skippie10]

Very interesting....I did some "looking" on the web site suggested for engine parts for Yanmar and the mounts I have do not look similar. I'll have to dig a bit deeper but thanks! Don

 

[Allan12210]

Very interesting....I did some "looking" on the web site suggested for engine parts for Yanmar and the mounts I have do not look similar. I'll have to dig a bit deeper but thanks! Don

Can you post a picture of your current mounts? It could help us figure out what you have.

 

[Skippie10]

Photos of Yanmar mounts and shaft output

Hope the photos are attached....have not tried this process before. Checked motor mounts and they are snug and seem in great condition. No looseness and no bulges/cracks.

I do have a folding prop but it has a gear device which requires that the two blades open evenly.

It might be a misalignment problem but the only mechanic around town is very busy and is quitting work to sell boat parts on e-bay!?

So, if I knew how to do alignment via a youtube video or similar, I would attempt checking it. Does anyone know a quick learn video on alignment?

Skippie

 

[Allan12210]

Hope the photos are attached....have not tried this process before. Checked motor mounts and they are snug and seem in great condition. No looseness and no bulges/cracks.

I do have a folding prop but it has a gear device which requires that the two blades open evenly.

It might be a misalignment problem but the only mechanic around town is very busy and is quitting work to sell boat parts on e-bay!?

So, if I knew how to do alignment via a youtube video or similar, I would attempt checking it. Does anyone know a quick learn video on alignment?

Skippie

Well, those are Yanmar mounts all right. Can't tell much by looking at them, but eventually they can get soft and its easy to move the engine about.

Here's a description of how to align the shaft.

 

[Benny17441]

If you can easily move the engine from side to side by hand they are likely worn. If you can pick up the engine from one support point end and elevate it that mount is split and broken. Nice pictures but cannot tell by their looks. Beware of some cleaning products that tend to deteriorate rubber. The prop might be very well designed to have both blades open simultaneously but have you verified it is properly working? That mechanism can wear down and fail to work as advertised. Everything related to that fault needs to checked, do not make any assumptions.

 

[Skippie10]

One more point....when I say that the engine shakes the boat, I can tell you (from my meager years as an amateur engine tuner) that it also feels like the engine is running on 2 cylinders vs 3....like there is a "miss" in the engine firing.

Again, it doesn't do this when I have it in neutral - only when under load and I try to move up in speed from idle with a "quick" move of the throttle. Similar to the days when we had carburetors and when you stepped on the gas, you had a miss and things chugged along (those were the days!).

By the way, the engine has never been "tuned" nor "cleaned" in any way and for 25 years, we never exceeded 2400 rpm - we were told by the original owner to keep the rpms below 2400 so we don't wear out the engine prematurely...I now, understand that this is bad practice...so, maybe all those years of slower rpms is part of the problem?

I'll be doing a final check on alignment in next several days.

Don

 

[kloudie1]

Don, I can't see the aft ends of the engine mounts very well in the picture but it does look like the top (movable) metal piece of the mount is very close to the bottom fixed metal piece. Someplace in the literature, I think I remember that the gap between the top and bottom metal parts should not be less than 1/4".. Usually if the rubber has collapsed to where the metal is striking top-to-bottom, you could see the marks on the bottom of the mount.. look carefully.. If you see one that has been touching, you may rotate it 180 before alignment to get it loaded a different way. and temporarily stop the racket. The 3 cyl engines shake A LOT at low RPM.... the Yanmar mounts are quite soft to allow that but when things hit together, it makes a lot of noise..