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Old 29-07-2013, 02:25   #1
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Loud Banging from a Yanmar 2gm20

the engine is in neutral so I guess it rules out the shaft? seems to be there regardless of rpm, or fwd/rev.

I'll take a closer look soon, but would be grateful if someone has had similar experience to help me zoom in on what to look at.

Here's a video, please ignore the nicro fan I was fixing... the loud banging is the engine in neutral...

MOV_0209_zps0e9a7909.mp4 Video by rockstock_car | Photobucket

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Old 29-07-2013, 11:25   #2
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Re: Loud Banging from a Yanmar 2gm20

If your lucky its just a bad engine mount, which is what it sort of sounds like to me. Other things it could be is bad / spun big end bearing.

Hows the oil pressure?

I should note that I just found a delaminated engine mount on my 3gm, so it does happen

Quote:
Originally Posted by Salted View Post
the engine is in neutral so I guess it rules out the shaft? seems to be there regardless of rpm, or fwd/rev.

I'll take a closer look soon, but would be grateful if someone has had similar experience to help me zoom in on what to look at.

Here's a video, please ignore the nicro fan I was fixing... the loud banging is the engine in neutral...

MOV_0209_zps0e9a7909.mp4 Video by rockstock_car | Photobucket

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Old 29-07-2013, 19:42   #3
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Re: Loud Banging from a Yanmar 2gm20

Thanks SC,

bad mounts did cross my mind, or that the engine wasn't bolted securely to the mounts.

I'll be looking at her again this weekend, and check on the other bits.

Thanks for the tip!
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Old 29-07-2013, 19:48   #4
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Re: Loud Banging from a Yanmar 2gm20

how long have you had it, when did the noise start? What have you done to it recently?
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Old 29-07-2013, 19:51   #5
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How is your oil pressure? Does the noise to away or get quieter as you increase the throttle? What has changed with your engine recently?

I had my engine make a similar but a little higher pitched sound that was caused by a bad belt. I never would have guessed it and it was right after a new head gasket. Nothing I did should have caused the noise. It turned out that the belt going bad was simply a coincidence. The slightly different tension after reassembling must have brought out the problem. Changed the belt and it ran perfectly. I did have some serious doubts for about 45 minutes.
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Old 29-07-2013, 20:08   #6
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Re: Loud Banging from a Yanmar 2gm20

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Originally Posted by charliehows View Post
how long have you had it, when did the noise start? What have you done to it recently?
Hi Charlie, I'm a noob, and this is my first boat, and I think I've been hearing it since I had her a few months. I've not done anything nor am I capable of, yet...

The previous owner did change her oil/filter before handover though.

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Originally Posted by Tim R. View Post
How is your oil pressure? Does the noise to away or get quieter as you increase the throttle? What has changed with your engine recently?
...
Changed the belt and it ran perfectly.
Hi Tim,

Throttle does not seem to affect the volume, just the frequency, proportionately, if my memory/hearing serves me correctly. With this observation I hope it'll be as benign as mounting issues...

I'll be checking your pointers out this weekend...

Thanks for the help guys!
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Old 29-07-2013, 21:03   #7
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Re: Loud Banging from a Yanmar 2gm20

I finally listened to the sound on the video. I don't hear a loud banging sound. My friend has a 2GM similar to this model and it sounds pretty much like the sound in the video.

Does the motor bounce a lot when running?

Is the motor capable of driving the boat speed above 5 knots in smooth water?
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Old 29-07-2013, 21:12   #8
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Re: Loud Banging from a Yanmar 2gm20

Quote:
Originally Posted by transmitterdan View Post
I finally listened to the sound on the video. I don't hear a loud banging sound. My friend has a 2GM similar to this model and it sounds pretty much like the sound in the video.

Does the motor bounce a lot when running?

Is the motor capable of driving the boat speed above 5 knots in smooth water?
that's what the previous owner said too, but part of me just can't imagine/accept an engine designed to make such a racket... hence this thread

Yes, she does do 5-ish +-, and I'll look for bouncing too, this weekend...
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Old 29-07-2013, 21:30   #9
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Re: Loud Banging from a Yanmar 2gm20

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Originally Posted by Salted View Post
that's what the previous owner said too, but part of me just can't imagine/accept an engine designed to make such a racket... hence this thread

Yes, she does do 5-ish +-, and I'll look for bouncing too, this weekend...
It's a 2 cylinder diesel. It can't be well balanced because of that. If it makes 5 knots without black smoke then both cylinders are firing. I think what you hear is normal.

Our 4 cylinder Yanmar was making a "banging" sound that I finally traced to the door to the head. At a certain RPM the door was vibrating violently. Once I found that I was able to cushion it and things got a lot quieter. Sometimes the sound is not coming from where you first think.
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Old 30-07-2013, 03:03   #10
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Re: Loud Banging from a Yanmar 2gm20

Quote:
Originally Posted by transmitterdan View Post
I finally listened to the sound on the video. I don't hear a loud banging sound. My friend has a 2GM similar to this model and it sounds pretty much like the sound in the video.

Does the motor bounce a lot when running?

Is the motor capable of driving the boat speed above 5 knots in smooth water?
Quote:
Originally Posted by Salted View Post
that's what the previous owner said too, but part of me just can't imagine/accept an engine designed to make such a racket... hence this thread

Yes, she does do 5-ish +-, and I'll look for bouncing too, this weekend...
I have a 2GM20 and it sort of sounds like yours, at least at idle. I am with transmitterdan on this one, check out if it vibrates a lot (bounces around).

Note that this motor will have resonant nodes at some points of the RPM range. It should be very stable at most power setting but you can expect it bounce around at some power settings. Obviously avoid these settings.

If it vibrates over most of the power range, then you may well have a bad mount(s).
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Old 30-07-2013, 08:05   #11
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Re: Loud Banging from a Yanmar 2gm20

Thanks guys! appreciate your taking the time to advise me!
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Old 30-07-2013, 09:17   #12
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Re: Loud Banging from a Yanmar 2gm20

I have two of these in my boat. Neither sound the same as the other. One has a louder diesel knock but that's normal. A good running two cylinder in neutral shouldn't vibrate too much. If you still feel you hear the noise in neutral and it is not bouncing I would doubt the motor mounts are the issue. I had a hard time hearing any out of order knocking on your video as well. When was the last time the valve lash was checked?
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Old 30-07-2013, 14:50   #13
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Hello Salted, I have a 2GM and it sounds about the same. I have had for 10 years now and just keeps plugging away.
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Old 30-07-2013, 15:18   #14
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Re: Loud Banging from a Yanmar 2gm20

There is a fix to the loud banging sound from the engine, which is to convert to electric propulsion.
Diesels in fact bang quite loudly, don't worry you'll get used to it, and the smell of diesel fuel, and the black smoke, soon you'll think this is the way all sailboats are supposed to be,
with a big heavy ugly obnoxious stinky polluting loud thing in your refined graceful quiet wind powered boat. :devil
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Old 30-07-2013, 15:35   #15
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Re: Loud Banging from a Yanmar 2gm20

Sounds like a normal 2 cylinder diesel to me.
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