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Old 28-11-2020, 15:57   #1
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Yanmar 3GM30f won't start

Greetings diesel wizards, what do you make of this? For the last few months my Yanmar 3GM30f (4,000+/- hours on the meter but I bought the boat used so who knows?) had been running rough for the first few minutes on start-up, then it smoothed out and ran fine. A couple of months ago, I started it and it ran VERY rough for a minute or two and then smoothed out. After a short time it smelled hot so I checked the exhaust water flow and there was none! Just black smoke and soot pouring out of the exhaust pipe. Before I could shut off the engine, it shut itself off. The engine compartment was filled with black smoke that smelled like burnt oil. I removed the air cleaner and noticed that the foam filter element was gone! Only the metal frame remained. I cranked the engine over and noticed smoke coming out of the intake manifold. I pulled the head and sent it to the machine shop. As expected, the exhaust valves were seriously burned. I had the valves ground and the head checked for true. I had the injectors serviced. I reassembled the engine, adjusted the valves and bled the fuel system. The engine still would not start. Not even if I used starting fluid. I can't imagine the the engine has slipped time but who knows. Any input and/or ideas before I order a new engine would be appreciated.
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Old 28-11-2020, 16:17   #2
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Re: Yanmar 3GM30f won't start

. Welcome to the forum.
Did you pull the pistons as well & check the rings?
Sorry if this is a dumb question but it isnt mentioned in your description.
I believe some of those engines were subject to piston/ ring failure. Good chance of damage if you had a serious overheat. Search for sailorchick s story on rebuild


Maybe it would be good to do a compression test & check that injectors are spraying before you trash the engine.
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Old 28-11-2020, 16:22   #3
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Re: Yanmar 3GM30f won't start

Since you've already done the head might want to rebuild the rest of it before going with a newer engine. Have 2 Yanmar GM's and they have been great engines and extremely reliable though not with near the hours you've got on yours. Going with a different engine usually involves a lot of changes to exhaust, mounts, shaft, etc that can get real expensive if if you are paying a mechanic to do it making rebuilding your engine way cheaper in the long run. Also have seen used 3GM30F's show up relatively often so you might try and hunt down a used engine if you didn't want to go the rebuild route.

Running an engine without cooling till it seizes usually doesn't have a good outcome. Believe the Yanmar's are a sleeved engine so the block may be okay. First thing is to check if the casting has cracked. If it has a new or used engine is in your future. What did the bores look like when you had the head off??

Believe the new Yanmar's are electronically controlled common rail injection engines. Personally don't trust electronics in a marine environment so wouldn't even consider a new Yanmar.
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Old 28-11-2020, 16:34   #4
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Re: Yanmar 3GM30f won't start

Welcome aboard CF, Chris Cringle.

This may sound like a silly question but have you checked the exhaust manifold and water injection point (mixing elbow etc) for blockage.

These items can (and will) corrode and block up to the stage where the engine won't start.
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Old 28-11-2020, 17:07   #5
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Re: Yanmar 3GM30f won't start

Those are known for clogging the exhaust elbow. Pull and check the exhaust elbow. Some recommend checking the exhaust elbow annually, so if it hasnít been done, Iíd start there. Donít ask me how I know......
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Old 28-11-2020, 17:18   #6
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Re: Yanmar 3GM30f won't start

Check out FBís Yanmar Marine Engineís Owners Group..
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Old 29-11-2020, 09:55   #7
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Re: Yanmar 3GM30f won't start

Thank you to everyone for your quick and well thought-out suggestions. I will try to respond to all of your comments in this one post. I did not pull the pistons in order to check the rings, but I did kinda "jiggle" the pistons and there seemed to be some play in the rings. The cylinder walls looked good, as did the tops of the Pistons. The engine did not overheat to the point of seizing. It just died. It would easily crank moments after it died.I did not think of the possibility of a clogged exhaust elbow. I will check that. Over the years I have gone both the re-build and replace routes. The hassle factor is about the same to me. Since this will probably be my last boat (number 31) and I don't know for sure how many hours (and dirty little secrets) the engine has, my tendency is to et a new engine and live the remainder of my boating life in peace.
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Old 29-11-2020, 10:04   #8
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Re: Yanmar 3GM30f won't start

A compression test would go a long way to diagnose your problem.
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Old 29-11-2020, 10:11   #9
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Re: Yanmar 3GM30f won't start

I would check the exhaust elbow first, a known problem.
Also, they can break pistons and still run, but be hard to start and rough at low rpm etc.
The ring land cracks and the piece just floats in there.
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Old 29-11-2020, 14:37   #10
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Re: Yanmar 3GM30f won't start

Stay away from started fluid, it strips your cylinder walls of lubrication.
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Old 29-11-2020, 15:04   #11
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Re: Yanmar 3GM30f won't start

I dont have the fear of starting fluid as others do, but for your diesel, a spray bottle with diesel in it, or WD40 will start it up. If it wants to run with that, but not otherwise, you have a fuel problem.
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Old 29-11-2020, 15:33   #12
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Re: Yanmar 3GM30f won't start

Quote:
Originally Posted by Chris Cringle View Post
Thank you to everyone for your quick and well thought-out suggestions. I will try to respond to all of your comments in this one post. I did not pull the pistons in order to check the rings, but I did kinda "jiggle" the pistons and there seemed to be some play in the rings. The cylinder walls looked good, as did the tops of the Pistons. The engine did not overheat to the point of seizing. It just died. It would easily crank moments after it died.I did not think of the possibility of a clogged exhaust elbow. I will check that. Over the years I have gone both the re-build and replace routes. The hassle factor is about the same to me. Since this will probably be my last boat (number 31) and I don't know for sure how many hours (and dirty little secrets) the engine has, my tendency is to et a new engine and live the remainder of my boating life in peace.

Yes I can see your reasoning if you have the dollars & you clearly have the boating experience.
Exhaust elbow a good check to do & post #11 is a good test as well.

Don't know where in the world you are but Beta/Kubota repowers seem to be popular here based on much lower parts prices & non electronic engines. I have no association with Beta but I do have an experienced based fear of local yanmar, volvo & Bukh parts prices.
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Old 29-11-2020, 16:54   #13
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Re: Yanmar 3GM30f won't start

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Originally Posted by Wotname View Post
Welcome aboard CF, Chris Cringle.

This may sound like a silly question but have you checked the exhaust manifold and water injection point (mixing elbow etc) for blockage.

These items can (and will) corrode and block up to the stage where the engine won't start.
I have never seen a blocked exhaust manifold... what blocks it?
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Old 29-11-2020, 17:02   #14
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Re: Yanmar 3GM30f won't start

Compass 790, Yes, if I decide to re-power, I will definitely choose a Beta. I have been shipmates with Beta engines before and like them a lot. I am embarrassed that I did not think of the exhaust issue myself and will check that out ASAP. Hopefully, no new engine will be required.
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Old 29-11-2020, 17:21   #15
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Re: Yanmar 3GM30f won't start

30 years worth of 2gm and 3GM Yanmars. They eat those foam silencer elements all the time. I finally just quit fooling with mine, just have the metal support frame. The mixing elbows will clog with carbon and rust in a few years. I just replace mine every 4 or 5 years. Using a SS one off ebay (now 5 YO, a record).

I have found them to be reliable and trouble free (change the oil every 50 to 100 hours). My 3GM (3500 hrs) will be a little hard to start if not cranked for a couple of weeks. Think it is a little air getting into fuel system. If you have reworked the head might want to continue with the troubleshooting. They are just great engines. Would not be in too big a hurry to just toss it out.


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