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15-07-2012, 10:15
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#1
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Registered User
Join Date: Jul 2012
Posts: 3
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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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15-07-2012, 10:30
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#2
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Registered User
Join Date: Feb 2012
Location: Punta Banda, Ensenada. and Canada
Boat: 28Ft Piver Encore, Tri-Maran, Anchored in San Diego.
Posts: 728
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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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15-07-2012, 10:34
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#3
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Registered User
Join Date: Oct 2008
Posts: 223
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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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15-07-2012, 11:01
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#4
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Registered User
Join Date: Jul 2012
Posts: 3
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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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15-07-2012, 11:15
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#5
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Registered User
Join Date: Feb 2012
Location: Punta Banda, Ensenada. and Canada
Boat: 28Ft Piver Encore, Tri-Maran, Anchored in San Diego.
Posts: 728
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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..
Quote:
Originally Posted by isidor
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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15-07-2012, 12:52
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#6
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 21,188
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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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15-07-2012, 16:59
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#7
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Registered User
Join Date: Jun 2007
Location: SW Florida
Boat: FP Belize, 43' - Dot Dun
Posts: 3,823
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Re: yanmar 3GM30F has rattling sound when starting
Cold diesels rattle.
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15-07-2012, 17:12
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#8
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Registered User
Join Date: Aug 2008
Location: Wash DC
Boat: PETERSON 44
Posts: 3,165
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Any chance the damper plate has failed?
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15-07-2012, 20:07
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#9
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 21,188
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Re: yanmar 3GM30F has rattling sound when starting
Ours does not rattle cold.
b.
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15-07-2012, 21:32
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#10
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Registered User
Join Date: May 2011
Location: Los Angeles
Boat: C&C 38
Posts: 55
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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.
Ron
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16-07-2012, 00:35
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#11
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Registered User
Join Date: Mar 2009
Location: Australia, Hervey Bay QLD
Boat: Boden 36 Triple chine long keel steel, named Nekeyah
Posts: 909
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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,
Richard.
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16-07-2012, 14:39
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#12
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Registered User
Join Date: Jul 2012
Posts: 3
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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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19-07-2012, 11:04
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#13
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Registered User
Join Date: Aug 2003
Boat: Dragonfly 1000 trimaran
Posts: 7,274
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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.
__________________
'You only live once, but if you do it right, once is enough.
Mae West
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19-07-2012, 11:58
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#14
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Registered User
Join Date: Mar 2006
Posts: 1,594
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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
__________________
Randy
Cape Dory 25D Seraph
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19-07-2012, 16:02
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#15
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 21,515
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Re: yanmar 3GM30F has rattling sound when starting
Quote:
Originally Posted by isidor
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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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.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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