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Old 11-11-2013, 11:10   #1
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Yanmar has the Shakes

Bought this boat back in April with 70 hours on it. Have put about 200 hours on the 3 cyl yanmar 40hp. So, 270 hours on it.

I noticed a progressive issue about 40 hours back.

From day one, it seemed like the engine just took a good 10 minute warmup or so to idle smoothly. I figured that was normal. Eventually, it seemed as though the fully warmed engine was not idling smoothly. Sometimes, another few minutes under power and it would idle fine. Sometimes, not. Now, it pretty much tries to shake the boat apart at idle no matter how long it's been running.

It doesn't matter if it's in gear or neutral, it shakes like hell.

It doesn't smoke. Motor mounts look good. Idle is set at 825-850. It operates at full rpm, although there may be a 100 rpm or so drop in max speed. Not sure about that.

It starts easily, accelerates smoothly, shuts down easily, etc.

Both the primary and secondary filters have been changed, recently. No evidence of fuel issues found there.

One curious issue- when opening the bleed screw on the secondary filter system, I had to pump the little lever on the fuel pump about 25 times before fuel appeared. However, it was solid fuel when it appeared. Also, that bleed operation had no effect on the idle shaking.

Advancing the the throttle instantly stops the shakes. However, advancing it to say, 900 and then stopping, the shakes come back, immediately. Around 1000 rpm, the shaking becomes what I would call normal although I hear a slight knock, like one unhappy cylinder.

The idle stop screw is tight and the plate is firmly against it.

I'm ruling out cable stretch, motor mounts and filter issues.

Time to pull the injectors and clean them?
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Old 11-11-2013, 11:32   #2
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Re: Yanmar has the shakes

Do not just look at the motor mounts. Put a wrench on every nut on them and make sure all is tight.

Next, make sure that the rubber on the mounts is not broken away from the steel mount. You can only see this be looking closely at the mounts when the engine is running.
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Old 11-11-2013, 11:40   #3
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Do not just look at the motor mounts. Put a wrench on every nut on them and make sure all is tight. Next, make sure that the rubber on the mounts is not broken away from the steel mount. You can only see this be looking closely at the mounts when the engine is running.
Done all of this, thanks.

All of the rubber is firmly attached and all of the nuts are tight.
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Old 11-11-2013, 11:47   #4
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Re: Yanmar has the shakes

I would have the injectors tested, although 270 hours is nearly nothing. If it was a bit hard starting I would suspect a piston failure.
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Old 11-11-2013, 11:56   #5
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Re: Yanmar has the shakes

My initial stab in the dark would be you are not getting enough fuel at idle to one of the cylinders and when you advance the throttle it is able to overcome whatever restriction there is and run "normally". again just a guess but possibly something partially clogging one of the injectors
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Old 11-11-2013, 11:58   #6
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My initial stab in the dark would be you are not getting enough fuel at idle to one of the cylinders and when you advance the throttle it is able to overcome whatever restriction there is and run "normally". again just a guess but possibly something partially clogging one of the injectors
This is what I'm starting to think, too.
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Old 11-11-2013, 12:33   #7
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Re: Yanmar has the shakes

I also would be looking at the fuel. How old are the filters? How old is the fuel? Have to tried running the engine using a nice clean pail of diesel and fresh filters (or bypass filters if using a nice fresh container of clean fuel)?
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Old 11-11-2013, 12:34   #8
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Re: Yanmar has the shakes

filters are 20 hours old. the filters they replaced looked fine.

The fuel is quite fresh, too.


This seems to have slowly progressed over 200 hours to where we are now.
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Old 11-11-2013, 12:48   #9
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Re: Yanmar has the shakes

As well as checking the injectors I would do a compression test. If possible do a leak down test with piston at both top and bottom of the cylinder.
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Old 11-11-2013, 12:57   #10
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Re: Yanmar has the shakes

Another thought to try and minimize your diagnosis time. Go to sears and for 20 or 30 bucks pick up a laser temperature gun and check how hot the exhaust is at each cylinder at idle if one is sufficiently cooler than the rest then you know at least where to start. If they are all the same then you "could" have way bigger issues.
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Old 11-11-2013, 13:11   #11
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If you have ruled out injectors , ( just undo one at a time and see if the revs decrease on the good ones , put a rag around it before you undo 1/4 to 1/2 a turn) and fuel supply, the lift pump may be your problem, if it's worked off a cam just flick the ignition for a second to reposition , there should be a more positive resistance on the lever when manually pumped.
Could be the injector pump has rotated and is now miss timed, but I would have thought starting would be a problem or smoke would increase.
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Old 11-11-2013, 13:13   #12
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Another thought to try and minimize your diagnosis time. Go to sears and for 20 or 30 bucks pick up a laser temperature gun and check how hot the exhaust is at each cylinder at idle if one is sufficiently cooler than the rest then you know at least where to start. If they are all the same then you "could" have way bigger issues.
That's a good idea. I have access to a high resolution ir camera.
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Old 11-11-2013, 14:09   #13
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Re: Yanmar has the shakes

Yanmar engine mounts can look good, but the rubber can become delaminated from the metal. The signs is rubber curling up away from the edge of the metal. If you have any of that, odds are one edge of the rubber has come loose. Happened to me.

Also check prop shaft alignment.
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Old 11-11-2013, 15:42   #14
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Very first thing, do what was suggested, while she is shaking, slowly loosed the "b" nut on each injector, when you loosen that nut, that cylinder stop firing as it has no fuel, if you find a cylinder that it makes little or no difference on, that the one with what I think is a dirty / plugged injector. I'll even go so far as to suggest that techron and or sea foam might be all it takes to clean this injector. Yes, I'm betting on a dirty injector, especially when I heard you say it sounds like it has picked up a little knock too, that along with the rough idle is classic of dirty injecotrs
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Old 11-11-2013, 15:57   #15
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Very first thing, do what was suggested, while she is shaking, slowly loosed the "b" nut on each injector, when you loosen that nut, that cylinder stop firing as it has no fuel, if you find a cylinder that it makes little or no difference on, that the one with what I think is a dirty / plugged injector. I'll even go so far as to suggest that techron and or sea foam might be all it takes to clean this injector. Yes, I'm betting on a dirty injector, especially when I heard you say it sounds like it has picked up a little knock too, that along with the rough idle is classic of dirty injecotrs
Thanks. My uncle sells diesel tractors and he said to sea foam it and relax for a tank of fuel.

I'm gonna do just as you say. I'd like to isolate the problem and then try an easy fix, first.
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