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Old 15-07-2012, 10:15   #1
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pirate yanmar 3GM30F has rattling sound when starting

When I start my engine, I get a loud rattling sound that lasts for about 10 seconds and then goes away. The rattling noise does not return until the next time I start the engine. Sounds like loose washers. Checked engine mounts, pulleys, and any externally mounted parts but nothing is loose.
Oil pressure is normal, runs fine under load.
Any ideas?
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Old 15-07-2012, 10:30   #2
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Re: yanmar 3GM30F has rattling sound when starting

Might be low oil pressure to the top end when starting,,making the valve train rattle a bit.
I would use a mechanics stethoscope,(or a piece of wooden doweling put to the ear) ,and listen closely when it happens and see if you can track it down.
If you are mechanically inclined, you might want to remove the valve cover and check for rockers loosening and such.

Better to find out now while its still just a rattle.
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Old 15-07-2012, 10:34   #3
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Re: yanmar 3GM30F has rattling sound when starting

How many hours on the engine?

This engine does sound rattly until a load is applied.

Do you have a smart regulator on your charging system (like a Balmar)? The regulators delay voltage ramp-up (and loading up the engine) until the engine is running for about 30 seconds or so (its configurable).

This is my setup and the engine (1000 hours) does "rattle" until the regulator loads up the engine.

Thought is it could be valve clearance as they can get quiet when the engine warms up. But 10 seconds seems too quick.
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Old 15-07-2012, 11:01   #4
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Re: yanmar 3GM30F has rattling sound when starting

I did check the valve gaps which were good. I did notice that the rocker arm for cylinder 3 exhaust valve had more side ways play (when moved forward and backwards) than all the others. Looked like a washer shim would be needed to take the play out.
I'll try the wooden stick to locate the noise.
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Old 15-07-2012, 11:15   #5
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Re: yanmar 3GM30F has rattling sound when starting

Just thought of another source to the Rattling,,,do you have a drive belt tensioner pulley?
Could indicate bearing or bushing sleeve wear,,,just a guess..



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I did check the valve gaps which were good. I did notice that the rocker arm for cylinder 3 exhaust valve had more side ways play (when moved forward and backwards) than all the others. Looked like a washer shim would be needed to take the play out.
I'll try the wooden stick to locate the noise.
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Old 15-07-2012, 12:52   #6
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Re: yanmar 3GM30F has rattling sound when starting

If the sound was not there before and now it is there, then it is bad.

If it is any issue with oil (?) then the second time you start, the issue should not be there.

Is there any probability the sound is related to the starting motor (e.g. not disengaging)?

b.
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Old 15-07-2012, 16:59   #7
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Re: yanmar 3GM30F has rattling sound when starting

Cold diesels rattle.
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Old 15-07-2012, 17:12   #8
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Any chance the damper plate has failed?
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Old 15-07-2012, 20:07   #9
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Re: yanmar 3GM30F has rattling sound when starting

Ours does not rattle cold.

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Old 15-07-2012, 21:32   #10
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My 3QM30 rattles for a few seconds. I assume it to be normal for a diesel with no glow plugs. I'm amazed it starts as easily as it does and a little detonation, if that's what it is, makes sense.

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Old 16-07-2012, 00:35   #11
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Re: yanmar 3GM30F has rattling sound when starting

You will probably find that is rattling until the oil pressure builds up. This is a classic symptom of a big end bearing with excess clearance and about to fail.
Regards,
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Old 16-07-2012, 14:39   #12
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Re: yanmar 3GM30F has rattling sound when starting

I found the source of the sound. It is the alternator. I did this by process of elimination. I removed the belt connected to the water pump and alternator pulley's, started the engine and no noise. I then a smaller belt only over the water pump pulley, leaving the alternator pulley unbelted. Started the engine and no noise. Finally I used another small belt only over the alternator pulley, started the engine and there was the noise.

I can feel some play in the alternator shaft, so it is most likely the bearing.

Also, I can operator the engine without the noise by leaving the pulley belt with additional slack. Next step is to remove the alternator and do the internal inspection.

Thanks for all the feedback.

Isidor
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Old 19-07-2012, 11:04   #13
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Re: yanmar 3GM30F has rattling sound when starting

We used to have a rattle on our previous boat's Yanmar.
It turned out to be a broken motor mount stud.
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Old 19-07-2012, 11:58   #14
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Re: yanmar 3GM30F has rattling sound when starting

ever stand beside an older F250 turbo diesel? It sounds like there are marbles in the combustion chamber..Some diesels rattle like hell until full temp/pressure is gained and then some still rattle like crazy at idle...stick a piece of tubing between your ear and the valve cover on start up and listen. Could very well be lacked of oil in the top end until oil pressure gets up and lubes the valve train.

BIG question! Did this JUST start?

Good luck
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Old 19-07-2012, 16:02   #15
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Re: yanmar 3GM30F has rattling sound when starting

Quote:
Originally Posted by isidor View Post
I found the source of the sound. It is the alternator. I did this by process of elimination. I removed the belt connected to the water pump and alternator pulley's, started the engine and no noise. I then a smaller belt only over the water pump pulley, leaving the alternator pulley unbelted. Started the engine and no noise. Finally I used another small belt only over the alternator pulley, started the engine and there was the noise.

I can feel some play in the alternator shaft, so it is most likely the bearing.

Also, I can operator the engine without the noise by leaving the pulley belt with additional slack. Next step is to remove the alternator and do the internal inspection.

Thanks for all the feedback.

Isidor
Thanks for letting us know what it was; it is always good to hear the final outcome - so many people post a question, get replies but never let us know the final answer.
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