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-   -   Yanmar 1GM10 runaway? (http://www.sailnet.com/forums/diesel/116081-yanmar-1gm10-runaway.html)

PaulinVictoria 01-08-2014 08:43 PM

Yanmar 1GM10 runaway?
 
Had an interesting experience at the weekend so just looking for some pointers, advice and the usual useful suggestions that always come from Sailnetters :p
Anyway, I was motoring out of the harbour, normal cruising revs which on mine is about 2800rpm, had the main up as I was going to sailing shortly. There was a clunking, sounded definitely transmission related and I had something similar previously (which I thought I'd fixed but there you go). Throttled back and into neutral, I have an Edson single lever control, back into forward, throttled back up and all fine again.
About 30 seconds later, same clunking, this time when I throttled back the engine revs climbed, and climbed. Back into neutral and off she went, revs up and up. I pulled the kill lever, no effect.
Mildly concerned by a hundred pounds of pig iron trying to destroy itself under my feet, I went below to pull the access covers off to get her stopped. Of course there were a bunch of things in the way so it took me about 30 seconds (a guess, time has a strange way of deceiving you in these situations).
Just as I was pulling the first access cover off, the revs dropped back down as if the throttle had been closed, and then she shut off (same as she does normally, kill lever was pulled remember).
She had revved so hard that one of the water hoses was starting to come off. I tightened everything up, checked what I could see and there was nothing obvious causing it.
After mulling my options, changing my underpants and so on, I fired her back up again, took a few seconds longer than usual but she fired and sounded pretty normal. I motored back to my slip at just above idle.
Went back to the boat Sunday and took the engine control covers off, all looked spotless in there, everything seemed to work smoothly. Couldn't see anything obvious anywhere, only slight tickle was the dipstick touching the throttle lever on the engine when the throttle was open. Bent that out the way. Fired her up, let her warm for a few minutes, revved in neutral no problem, ran her for several minutes in forward at about 2k rpm (can't go any higher when tied up, the load makes her smoke like a chimney), same in reverse at 3k rpm, nothing untoward.

So.... any thoughts on a cause, how to prevent it in future, anything else I need to check etc?

Seems somehow different to most/all the other things I have read about a runaway diesel, she was running at full throttle for at least a minute or two I would think, but never got to the destructive part where bits of engine were flying off and puncturing my hull.

In hindsight, I wish I had checked the throttle was closed at the engine end because that would have at least told me it was an actual runaway, but that's hindsight for you.

Faster 01-08-2014 09:29 PM

Re: Yanmar 1GM10 runaway?
 
Good detailed post.... unfortunately nothing helpful is occurring to me - mysterious...

fryewe 01-08-2014 10:32 PM

Re: Yanmar 1GM10 runaway?
 
Interesting scenario.

I think I would:
- check the oil level...check its viscosity by running it between my fingers...and smell it to see if there is diesel fuel in it.
- pull the governor cover and see if there is any obvious loose linkage or unexpected wear including fly weights and springs.

Then I would think some more and scratch my chin. And check my tech manual drawings and ponder some more.

PaulinVictoria 01-08-2014 10:39 PM

Re: Yanmar 1GM10 runaway?
 
On the positive side, I now know what a single cylinder diesel sounds like at 4000rpm :D

mitiempo 01-08-2014 11:30 PM

Re: Yanmar 1GM10 runaway?
 
Overfilling with oil can cause a runaway as the engine burns its lube oil. Were you at much of an angle - you said the main was up? I wonder if that could cause the lube oil to be ingested if it was higher on one side.

PaulinVictoria 01-08-2014 11:48 PM

Re: Yanmar 1GM10 runaway?
 
I was pretty much upright, there weren't even any waves. Oil was only overfilled if someone broke into my boat overnight and added some more, I did an oil change 42 engine hours ago so I'm pretty sure I would have seen this prior to the weekend, and I have motored in some pretty bouncy sea as well plenty of times.
Only think I can think of is that either it wasn't a runaway at all, rather a stuck throttle lever at the engine end or something like that, or that whatever caused it got used up allowing the engine to return to normal.
Either way, I don't really have an answer. I'll check the oil again at the weekend to see if it's magically got fuller (in which case I must have either diesel leaking into it, or the transmission oil is getting out and into the engine), take the air intake apart and see if there is oil in the filter, pull the governor cover off (will have to look in the book for that), anything else?

mitiempo 01-09-2014 12:02 AM

Re: Yanmar 1GM10 runaway?
 
If not lube oil then the governor could be the cause. I'm not a mechanic so just guessing.

PaulinVictoria 01-09-2014 12:03 AM

Re: Yanmar 1GM10 runaway?
 
With a runaway, wouldn't the revs just keep going up and up as the increased revs draw in more fuel, more air and so on? I'm pretty sure it revved to a point but no further. Admittedly that point was somewhat higher than I would normally expect the revs, but then I wasn't looking at the tacho.

mitiempo 01-09-2014 12:07 AM

Re: Yanmar 1GM10 runaway?
 
Quote:

Originally Posted by PaulinVictoria (Post 1288562)
With a runaway, wouldn't the revs just keep going up and up as the increased revs draw in more fuel...

Until the fuel (lube oil) couldn't be drawn up any more, yes as far as I know.

Dog Ship 01-09-2014 07:44 AM

Re: Yanmar 1GM10 runaway?
 
It's not just fuel that is being drawn in, engine oil can combust too.
Your crankcase is vented through a crankcase ventilation tube that returns crankcase gases back into your intake.
If the engine is worn enough to create blow-by via the piston rings or you have too much oil in the crankcase or worse fuel in your oil via a fault in the fuel rail. You have a recipe for disaster.
The crankcase gases will feed into your intake via the crankcase ventilation tube. Once they become combustible you have a runaway condition.
You can shut off the fuel but the engine with keep running off of the crankcase gases. It will start to increase in rpm which will promote this situation and so on and so on. The engine will start to create so much oil mist that it will continue to increase in rpm until it has a mechanical failure or runs out of oil and seizes. You got lucky somehow.
I'm going to take a guess and say that there is no fuel in your oil and your oil level was a bit to high and/or your rings are worn.
If it happens again you can smother the intake, you can decompress the engine with the decompression lever or you can give it a shot with a fire extinguisher into the intake and put the fire out.
One way or the other you are going to need some engine work done.
Sorry to hear this Paul.


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