Yanmar 3GMD sudden increase invibration - SailNet Community
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post #1 of 9 Old 08-30-2012 Thread Starter
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Yanmar 3GMD sudden increase invibration

Yanmar 3GMD issue: Yesterday, I was motoring along at around 2500 or so (mid-range anyway) and there was a sudden moderate increase in vibration. Seemed like it might have been picking up a block of seaweed, etc. at first. Reversed for a bit, with no change, so kept on since it was not a feeling of something major. It continued until the end of the day (much of it was under sail not power, by the way), so now I have to get into a diagnosis. First look will be at the prop, to be sure it is clean and free. The shaft is completely enclosed in the skeg. Assuming the prop is good, I don't have any real idea of what to check for next. The motor idles OK, starts fine, is smooth in gear at idle and a few hundred higher, then starts to add vibration in excess of its usual level. Gets worse up to around 23-2400, then gets smoother and seems sort of normal at higher speed.(26-3400). No signs of black smoke (or any smoke, really). Power seems Ok too, but that is hard to really test because the boat is well overpowered and could easily reach hull speed with a smaller motor. I'll check the coupler, shaft movement, any sign of run-out as it spins, any looseness of motor mounts (as best I can), any sign of fuel leakage. It would not seem to be a fuel starvation issue, or air leak into the fuel. I could picture the vibration being somewhat similar as the norm for operation of a 2 cylinder motor, but I really am just guessing here as I don't have any experience with those. Are there potential ways for it to have dropped out a single cylinder? Injector gone bad? that would possibly fit the bill, since no fuel being injected so no added black, unburned fuel in exaust. Could this be tested merely by opening each decompression lever in turn with the motor runing? I would be a little afraid of opening these with a running motor, but is it OK to do?

Anyway, I'd appreciate all ideas on what to check this weekend.

Thanks

Mike sullivan
1985 Marshall 22 catboat
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post #2 of 9 Old 08-31-2012
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Re: Yanmar 3GMD sudden increase invibration

Seems that you are running on all 3 cylinders at higher rpm's, but you can flip your decompression levers 1 cylinder at a time to see
if there is any change in vibration at the problematic rpm range.
If no difference when lever flipped then you know where to start
looking.
But basics like checking your prop and changing fuel filter (if not
changed recently) would make sense first.
Also, if you haven't already, run the motor through idle to higher rpm's in neutral.
Also how old/# of hours is motor, how long have you owned?
You know maintenance history?
How fresh/long has fuel been in tank? Old fuel with water will grow nastys in the tank. Primary (racor) filter changed/checked/drained of any water?
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post #3 of 9 Old 08-31-2012 Thread Starter
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Re: Yanmar 3GMD sudden increase invibration

Thanks for the ideas. The motor is 1985, but only 500 or so hours. I have had it for past three years, and prior owner had it for around 8. Professionaly maintained by him, partly DIY by me. Interestingly, the prior owner was aboard with me when the vibration started - the first time he had been back aboard. I keep it in the Piscataqua River just up from Portsmouth Harbor, and run it for a least a half hour each way in and out of harbor. River is a very fast current, one of top three tidal estuaries in the US I am told, so the little Yanmar is worked pretty well - never just loafing and not well warmed up. I have put around 100 hours on it to date, with pretty flawless performance. It is very up to date for maintenance. All new wiring harnesses, impeller, hoses, all filters, shaft/cutlas/motor mounts, belts, mixing elbow removed and cleaned last season (didn't need it), etc. Racor replaced in spring, looked clear through the glass, but I didn't open it yet. Fuel is of mixed age - did my first 2012 fill a couple of weeks back, for 8 gallons used so far this season. Tank holds around 14 gal. so rest of it is still from last year. Always keep additives for biocides as well as water, etc. and bottom of tank (seen through the fill pipe) is mostly shiny, with a few visible black bits on bottom. No smell of any fuel leakage, no smoke of any kind, no odd noises, etc.

I will get into it tomorrow, and at lesat eliminate several possible sources. Good to know that I can open the decompression levers at any time, not just when starting (never have needed to do this with any diesel so far).

Mike sullivan
1985 Marshall 22 catboat
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post #4 of 9 Old 09-01-2012
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Re: Yanmar 3GMD sudden increase invibration

Sounds like your on top of your maintenance and the likely suspects...maybe one of our sailnetter mechanics will be able to give some direction.
Think I have same motor on my 1985-30" sloop..3 GMC
(C= saildrive) raw water cooled 22.5 h.p. Very reliable motor
bought new.
Made it up to Portmouth/Kittery from western Long Island Sound
early May last year. Did not have time to go up the Pitcataqua
River. Maybe next time were up there. Interesting as we have the
East River down here that also has very fast current...but is not a river either is actually a Tidal Strait. Come to think of it Long Island
Sound is not a sound at all...is actually an estuary.
Good luck with motor this weekend.
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Re: Yanmar 3GMD sudden increase invibration

In the interest of full disclosure and to add a little humor, the answer to my increased vibration is pure user error. Last week I was replacing thx oil pressure sender (previous thread) and left a small pair of vice grips holding a shift cable out of the way. After a half hour of running, the vice grips opened and fell onto the Yanmar block which resulted in magnifying the sound of a metal tool
rattling on the block. Simplest fix I ever needed ).
sawingknots and davidpm like this.

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post #6 of 9 Old 09-02-2012
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Re: Yanmar 3GMD sudden increase invibration

Good testimonial for doing the easy things first, something I didn't always do, finally learned to go slow. Thanks for the feedback.

Paul T
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Re: Yanmar 3GMD sudden increase invibration

Congratulations, you have joined a large, and ever growing not so elite club of which I am a prominent member.
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Re: Yanmar 3GMD sudden increase invibration

Just a side note our 3GMF has a slight vibration as you power through 1300- 1600 rpm. We have just replaced engine mounts, shaft , and cutlass also. Our mechanic has told me that's normal with the 3 series of Yanmar.

Dave


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post #9 of 9 Old 09-04-2012
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Re: Yanmar 3GMD sudden increase invibration

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Originally Posted by chef2sail View Post
Just a side note our 3GMF has a slight vibration as you power through 1300- 1600 rpm. We have just replaced engine mounts, shaft , and cutlass also. Our mechanic has told me that's normal with the 3 series of Yanmar.

Dave
I get the same thing with my 3gmd, good to know its normal, one less thing to deal with.
Regards
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