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Old 25-09-2012, 06:36   #1
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Yanmar 3GM 30 Hard Starting

I have a pair of 3GM30s, common fuel system.

One engine has become increasingly very difficult to start, and may not even start. As it is cranking, it sounds like it is firing, but when starter is disengaged, the engine dies out. If throttle is advanced more the engine may start, with a big puff of grey smoke and quickly builds up rpms. And once started, it runs perfectly.

Checked fuel filter, which hadn't been long changed, and it looked fine. Worried it might be serious (my attempt at starting was a complete failure, and the engine had run perfectly for hours the previous day!) I had a mechanic take a look. He saw the same symptoms, so he just bled the fuel, and it started. Figuring I just hadn't fully bled the fuel, and happy it was nothing more serious, I accepted this. But now the problem remains.

So when it next occurred I bled the fuel, but really didn't see any air bubbles.
The engine ultimately started, but this has become a frequent problem.

I'm not convinced this is a bleeding issue, but maybe it is. I should know this, but is there a check valve in the fuel line on the engine that may be leaking?

Any suggestions?
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Old 25-09-2012, 07:30   #2
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Re: Yanmar 3GM 30 Hard Starting

My engine exhibited exactly the same symptoms. Harder and harder to start. I presumed fuel bleeding. Crack the throttle to get it to start. Fine after start.

Turned out to be low compression and ultimately found burned and corroded exhaust valves. I would schedule a valve adjustment and compression check.
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Old 25-09-2012, 08:14   #3
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Re: Yanmar 3GM 30 Hard Starting

ggray:

The fact that your engine starts with a puff of smoke indicates that the problem is not fuel supply. So it could be one of two (or may be both) problems:

1. Low compression. With ring wear or valves not sealing it takes a few seconds for enough fuel to be injected to help seal the rings (less so with valves) so that compression will be enough for ignition. Look at the back of your engine and you will see a 1/2" black hose going coming from the valve cover. Disconnect it and run the engine at the dock in gear at 1000 rpm or so. Feel the end of the hose. Is it pulsing with exhaust gases? If so that is blow by and it is an easier indication of low compression than a compression test.

If you do get noticable blowby then do a compression test to confirm it. But usually the problem is #2.

2. Injectors: A bad injector spray pattern makes it tougher to fire and requires more compression so you have to crank longer as described above. Pull the injectors and get them tested (they will almost always test bad, that is the nature of those who do the testing). Replace them as it costs almost as much as a rebuild.

David
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Old 26-09-2012, 20:20   #4
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Re: Yanmar 3GM 30 Hard Starting

Thanks Dan and David
You have given me something to look into. I will first check that blow-by hose.

But if either of these were the problem, would the engine still seem to have normal power?
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Old 26-09-2012, 20:52   #5
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Re: Yanmar 3GM 30 Hard Starting

May be way off here... but I recently helped a friend with the same problem. I assumed a fuel issue and bled the system (there was a few bubbles) and it started once after that but then resumed the 'hard start'.

I could get it going by manually holding open the compression levers, holding the starter motor on and then slowly releasing the compression levers. I was stumped. Then a friendly mechanic in the anchorage said to tighten the ground wire to the block.

He was right. My friend had just had his starting switch replaced and I guess the worker didn't tighten back up the ground connection. We snugged it tight and the engine's fired up like a dream ever since. Just couldn't draw enough amps to run the starter motor properly.

Like I said I may be way wrong... but this worked and I was a amazed!
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Old 26-09-2012, 23:49   #6
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Re: Yanmar 3GM 30 Hard Starting

Quote:
Originally Posted by ggray View Post
Thanks Dan and David
You have given me something to look into. I will first check that blow-by hose.

But if either of these were the problem, would the engine still seem to have normal power?
There are other things that can cause this but unless you are a mechanic you will spend a fair amount of time on this.

I do not know your cause but my engine exhibited exactly the same symtoms including the puff of smoke on start - I atributed to lots of unbirned fuel finally catching. For all appearances it ran normally after start except in hindsight when under heavy load it would smoke a bit which I atributed to fouling at the time.

The breather hose inspection will confirm bad rings but not bad valves. Bad valve guides would be accompanied by high oil consumption.
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Old 28-09-2012, 06:44   #7
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Re: Yanmar 3GM 30 Hard Starting

Not problem with cranking speed, so it's not an elictrical problem, but thanks anyway.

Quote:
Originally Posted by Aussie_Sequoia View Post
May be way off here... but I recently helped a friend with the same problem. I assumed a fuel issue and bled the system (there was a few bubbles) and it started once after that but then resumed the 'hard start'.

I could get it going by manually holding open the compression levers, holding the starter motor on and then slowly releasing the compression levers. I was stumped. Then a friendly mechanic in the anchorage said to tighten the ground wire to the block.

He was right. My friend had just had his starting switch replaced and I guess the worker didn't tighten back up the ground connection. We snugged it tight and the engine's fired up like a dream ever since. Just couldn't draw enough amps to run the starter motor properly.

Like I said I may be way wrong... but this worked and I was a amazed!
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Old 28-09-2012, 06:46   #8
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Re: Yanmar 3GM 30 Hard Starting

Thanks Dan. Looks like I'll need to have a word with the mechanic who determined it was a bleeding matter...or find a new mechanic.

Quote:
Originally Posted by Ex-Calif View Post
There are other things that can cause this but unless you are a mechanic you will spend a fair amount of time on this.

I do not know your cause but my engine exhibited exactly the same symtoms including the puff of smoke on start - I atributed to lots of unbirned fuel finally catching. For all appearances it ran normally after start except in hindsight when under heavy load it would smoke a bit which I atributed to fouling at the time.

The breather hose inspection will confirm bad rings but not bad valves. Bad valve guides would be accompanied by high oil consumption.
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Old 28-09-2012, 08:51   #9
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Quote:
Originally Posted by ggray
I have a pair of 3GM30s, common fuel system.

One engine has become increasingly very difficult to start, and may not even start. As it is cranking, it sounds like it is firing, but when starter is disengaged, the engine dies out. If throttle is advanced more the engine may start, with a big puff of grey smoke and quickly builds up rpms. And once started, it runs perfectly.

Checked fuel filter, which hadn't been long changed, and it looked fine. Worried it might be serious (my attempt at starting was a complete failure, and the engine had run perfectly for hours the previous day!) I had a mechanic take a look. He saw the same symptoms, so he just bled the fuel, and it started. Figuring I just hadn't fully bled the fuel, and happy it was nothing more serious, I accepted this. But now the problem remains.

So when it next occurred I bled the fuel, but really didn't see any air bubbles.
The engine ultimately started, but this has become a frequent problem.

I'm not convinced this is a bleeding issue, but maybe it is. I should know this, but is there a check valve in the fuel line on the engine that may be leaking?

Any suggestions?
I have a 2QM15, circa 1978 so obviously different but I've had similar starting issues. I did a couple of things. Added a cetane booster/injector cleaner to fuel. We motored a lot this summer so burned though probably 20 gals of fuel that was 'liberally' modified with the additive. It seemed have made starting easier.

The other thing I started doing was letting the engine run at about 1,500 rpm in neutral for a minute or so when we return to our dock. My mechanic said it helps reduce carbon buildup and also lets a good amount of water run through the muffler reducing the amount of carbon residue sitting there for the next start-up.

These two changes have made a very positive difference on how easy it is to start the engine. I open the throttle to about 80%, hit the starter and within five revolutions she is running.

I do plan on a valve adjustment over the winter as that has never been done in the eight years we've owned her.
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Old 28-09-2012, 19:22   #10
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Re: Yanmar 3GM 30 Hard Starting

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Originally Posted by David W View Post

These two changes have made a very positive difference on how easy it is to start the engine. I open the throttle to about 80%, hit the starter and within five revolutions she is running.
Wow, 80%? That seems a lot.
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Old 28-09-2012, 20:13   #11
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Re: Yanmar 3GM 30 Hard Starting

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Wow, 80%? That seems a lot.
Thinking about where the lever actually is, it is probably close to the factory spec in the Owners Manual of 50% and not 80%.
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Old 28-09-2012, 20:23   #12
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One time I had trouble starting my 3gm30 and after much time I found the stop handle out just a little. Pushed it back and bobs your uncle
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Old 01-10-2012, 20:47   #13
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Re: Yanmar 3GM 30 Hard Starting

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One time I had trouble starting my 3gm30 and after much time I found the stop handle out just a little. Pushed it back and bobs your uncle
Yeah, that was my first hope. But not to be.
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Old 01-10-2012, 21:12   #14
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Re: Yanmar 3GM 30 Hard Starting

The gray smoke indicates unburned diesel and low compression. Pulling the hose for checking blow by will implicate rings if you have the blow by. Did you have black smoke for a while perhaps caused by a bad injector? That would cause excessive cylinder wear and blow by. I am thinking you will have to pull the engine and get the head off to check cylinder wear if there is blow by and put a new cylinder liner and piston in.
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Old 01-10-2012, 21:48   #15
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Re: Yanmar 3GM 30 Hard Starting

Just happened across this thread and got very curious as I have been having a similar problem recently with my 3GM30.

Something that no one else has mentioned, however, is whether they are having a hard start every time, or only sometimes?

On mine, it starts hard the first time I start it on a given day. After that, it starts up normally and easily.

I thought at first that it was simply having trouble with a cold start, but that's not it... although it will start easily if warm, it starts equally easily when cold (after, say, eight hours of sailing). But let it sit for a day or two, and it's a hard start all over again.

Thought at first it was the stop knob, as someone mentioned, but I've been checking it closely since this started and that doesn't appear to be it.

So, does that sound like the compression problem, or something else? I am guessing it could be, since if David is correct about the fuel sealing the rings during the first start, it might continue to seal them for some hours later but have evaporated/pooled by the next day. I'll definitely pull the hose and check for blow by.

On the other hand, like ggray, I don't notice any particular drop off in power once it has started, even under heavy load, which is something I've always heard associated with compression problems.

Anyway, glad to find this thread, appreciate any feedback anyone might have on the hard first start/easy the rest of the day phenomena!
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