YANMAR RUNAWAY! Lessons Learned...

[Wotname]

Originally Posted by Compass790

I think they would stop your 2qm15 in a runaway situation.
We have a ysm8 which is basically 1/2 of a 2qm15 & I'm sure the decompression lever would kill it but the noise of the piston hitting the valve would be disconcerting to say the least.
Diesel just cant run without compression.
I dont like using the decomp lever to kill it & it says not to in the manual but I wouldnt hesistate to use it if I couldnt stop it by putting my hand over the air intake after I'd pulled the air cleaner off.
We dont have the Yammer original silencer/air cleaner setup.
I noticed no difference in noise levels with Yammers silencer removed & it cant clean air in Yanmars setup so replaced with oiled foam filter.

Are you sure the piston hits the exhaust valve when decompressed in the YSM.

It doesn't in the YSE, GM and QM.

In fact if it did, it would make the decompression function fairly useless, in what circumstance could you use it?

[Compass790]

Originally Posted by Wotname

Are you sure the piston hits the exhaust valve when decompressed in the YSM.

It doesn't in the YSE, GM and QM.

In fact if it did, it would make the decompression function fairly useless, in what circumstance could you use it?

Yes I'm sure & just coz the piston hits it doesnt mean it pushes up to the seat so it still leaks.
Mind you I operate by hand as the cable is knackered so trust me I can feel it hitting the v/v. It could be I'm opening it further than intended. i.e pushing the v/v too far down.

I use it to spin the motor up till the oil pressure alarm stops sounding i.e as a pre-oiler.
Dont want the engine to fire until oil pressure is 40psi actually & I'm watching the gauge whilst spinning it up decompressed.
Any more questions?

[Symphony]

great subject to think about.
if you're not expecting it, the sound is quite scary even at a distance.

1100 hp engines a bit different than my previous little Yanmars. I've got a fire blanket to smother the air intake.

[Bill Seal]

I'm sure the clattering you hear is just slop in the valve train because the decompression lever is holding the valve slightly off the seat. Sort of like a collapsed hydraulic lifter noise. If the piston would actually hit the valve, it would probably bend the pushrod even when hand cranking it.

[Wotname]

Originally Posted by Compass790

Yes I'm sure & just coz the piston hits it doesnt mean it pushes up to the seat so it still leaks.
Mind you I operate by hand as the cable is knackered so trust me I can feel it hitting the v/v. It could be I'm opening it further than intended. i.e pushing the v/v too far down.

I use it to spin the motor up till the oil pressure alarm stops sounding i.e as a pre-oiler.
Dont want the engine to fire until oil pressure is 40psi actually & I'm watching the gauge whilst spinning it up decompressed.
Any more questions?

Yep, one more question

How does the piston push the valve up towards the seat when there is no spring in the system. The decom lever is attached to the rocker cover and it holds the valve slightly depressed by pushing directly on the rocker arm and thus on valve stem.

If the piston pushed against the valve, it must also push against the rocker cover. There is no give in the system.

From the 2QM15 manual. I reckon the YSM is the same

[Wotname]

Originally Posted by Bill Seal

I'm sure the clattering you hear is just slop in the valve train because the decompression lever is holding the valve slightly off the seat. Sort of like a collapsed hydraulic lifter noise. If the piston would actually hit the valve, it would probably bend the pushrod even when hand cranking it.

Yes, the clattering is occurring as the cam operates the valve in the normal manner (via the pushrod). When decompressed, the exhaust valve opens as normal but when as it closes, the rocker arm (and valve stem) encounters the decompression lever and so stays slightly open. That is the noise / vibration which is coming from the decompression lever.

It the piston hit the valve (when decompressed), it would destroy something (likely the rocker cover).

[Wotname]

Originally Posted by Wotname

........

It the piston hit the valve (when decompressed), it would destroy something (likely the rocker cover).

EDIT - IF the piston hits the valve... etc.

[Montanan]

Originally Posted by Stu Jackson

Lovely thought: throw bits o'rag into your engine.


Sorry, just not buyin' it.

Ha, Stu, I believe the guidance and intention is to stuff cloth into the air intake leading to the air filter such that air entrainment is inhibited. Stuffing a rag directly into the air intake manifold would seemingly not work as it would likely just be pulled towards one cylinder and probably even pulled through an intake valve where it likely would then combust. The air filter seemingly will catch the cloth and restrict air flow. Just keep stuffing the air intake(s) for as long as the engine is sucking air. Including any of the auxiliary air intakes elsewhere leading into the engine block.

And not bits of rags but sizeable pieces of cloth, such as shirts, towels, or many of the 1 square foot sized work rags that are typically found in an engine compartment.

I recall one time a mechanic at a diesel repair shop, just took his boot off and slipped it over the intake such that it sucked the boot from the inside of the sole hard against the air intake opening and thence the engine slowed, stumbled and stalled.

[Montanan]

Originally Posted by Jammer

Thanks for sharing and glad it turned out ok.


Good to have a CO2 fire extinguisher around for these situations. They work a treat on runaway diesels. Not bad on fires, either.

Deploying a CO2 fire extinguisher in an enclosed space is highly hazardous, will not take long for the CO2 to out compete for your oxygen uptake and you pass out and die. Better be sure the CO2 is only going into the air intake of the engine and not flooding into the atmosphere of the engine room one is located in.

Reference: Carbon Dioxide as a Fire Suppressant: Examining the Risks https://www.epa.gov/snap/carbon-diox...xamining-risks


Snipets therefrom:

Carbon dioxide is used internationally in marine applications in engine rooms, paint lockers, vehicle transport areas on cargo vessels, and in flammable liquid storage areas (Willms 1998). Large marine engine room systems may require as much as 20,000 lb of carbon dioxide per system. Carbon dioxide fire suppression systems are currently being used by the U.S. Navy and in commercial shipping applications.

Extinguishing Mechanism of Carbon Dioxide

Flame extinguishment by carbon dioxide is predominantly by a thermophysical mechanism in which reacting gases are prevented from achieving a temperature high enough to maintain the free radical population necessary for sustaining the flame chemistry. For inert gases presently used as fire suppression agents (argon, nitrogen, carbon dioxide, and mixtures of these), the extinguishing concentration (As measured by the cup burner method (NFPA 2001)) is observed to be linearly related to the heat capacity of the agent-air mixture (Senecal 1999).
Although of minor importance in accomplishing fire suppression, carbon dioxide also dilutes the concentration of the reacting species in the flame, thereby reducing collision frequency of the reacting molecular species and slowing the rate of heat release.


Extinguishing Effectiveness of Carbon Dioxide
Carbon dioxide is the most commonly used "inert" gas extinguishing agent, followed by nitrogen. On a volume basis, carbon dioxide is approximately twice as effective as nitrogen (e.g., for ethanol fires, the minimum required volume ratios of carbon dioxide and nitrogen to air are 0.48 and 0.86, respectively). However, because carbon dioxide is 1.57 times heavier than nitrogen [44 and 28 molecular weight (MW), respectively] for a given volume, the two gases have nearly equivalent effectiveness on a weight basis.

The amount of carbon dioxide needed to reduce the oxygen level to a point at which various fuels are prevented from burning is relatively high and is also at a level where humans will suffer undesirable health effects.

Use of Carbon Dioxide Extinguishing Systems
Carbon dioxide fire extinguishing systems are useful in protecting against fire hazards when an inert, electrically nonconductive, three-dimensional gas is essential or desirable and where clean up from the agent must be minimal. According to the NFPA, some of the types of hazards and equipment that carbon dioxide systems protect are "flammable liquid materials; electrical hazards, such as transformers, switches, circuit breakers, rotating equipment, and electronic equipment; engines utilizing gasoline and other flammable liquid fuels; ordinary combustibles such as paper, wood, and textiles; and hazardous solids" (NFPA 12).


Life Safety Considerations of Carbon Dioxide
Health Effects
The health effects associated with exposure to carbon dioxide are paradoxical. At the minimum design concentration (34 percent) for its use as a total flooding fire suppressant, carbon dioxide is lethal.

At concentrations greater than 17 percent, such as those encountered during carbon dioxide fire suppressant use, loss of controlled and purposeful activity, unconsciousness, convulsions, coma, and death occur within 1 minute of initial inhalation of carbon dioxide. At exposures between 10 and 15 percent, carbon dioxide has been shown to cause unconsciousness, drowsiness, severe muscle twitching, and dizziness within several minutes. Within a few minutes to an hour after exposure to concentrations between 7 and 10 percent, unconsciousness, dizziness, headache, visual and hearing dysfunction, mental depression, shortness of breath, and sweating have been observed . Exposures to 4 to 7 percent carbon dioxide can result in headache; hearing and visual disturbances; increased blood pressure; dyspnea, or difficulty breathing; mental depression; and tremors.

[Compass790]

Originally Posted by Wotname

Yep, one more question

How does the piston push the valve up towards the seat when there is no spring in the system. The decom lever is attached to the rocker cover and it holds the valve slightly depressed by pushing directly on the rocker arm and thus on valve stem.

If the piston pushed against the valve, it must also push against the rocker cover. There is no give in the system.

From the 2QM15 manual. I reckon the YSM is the same

The give in the system is my hand on the actuating lever on the rocker cover & I can assure you my hand gives before the rocker cover does.
Also pretty sure that v/v can push my hand back before it bends the v[v stem.

As I said maybe my manual operation opens it more than the cable does.
Bill Seal, I'm not hand cranking it, I'm using the electric start.
Clattering could be the pushrod but I'll check to see if decomp lever is getting knocked to make v/v opening larger or smaller, that will answer the question.



Wottie if you check the clearance of a mostly open valve you will see it must contact the piston at TDC.The head is pretty flat & the piston rises fractionally above the liner top.That is, if the decomp lever opens it fully. Guess that is the big question. You would think they'd design it not to hit but....

Cant check as my spare head doesnt have the v/v's in it.

Thats my story & I'm sticking to it until I can check anyway.
Will post back when I closely observe behaviour of decomp lever in my hand on rocker cover. I think it knocks it back but my memory is not infallible.

Despite all the BS in this post I think its likely that I'm wrong as the rod that pushes on the rocker arm may not open the v/v enough to contact the piston but I dont know.



Bit of thread drift here but oh well.

[jimbunyard]

Originally Posted by SobeFlyer

I share this in the hopes it helps someone else....


I purchased a storm damaged sailboat and got to getting the Yanmar 4JH-TE running after almost two years unused. Fortunately a cousin is a marine diesel mechanic and he warned of a rare failure that will cause a runaway on a diesel that's been laid up for long periods.. the dreaded runaway. Yep, it happened to me, and I want to share lessons learned.


What happened...

After checking normal items, like oil quantity/quality, fuel quality, bleeding fuel lines to the injection pump, etc, I cracked each injector and cranked a bit to bleed possible air. I noticed rear injector was no juice when turning several revolutions. THIS SHOULD HAVE CAUSED ME TO ABORT A START ATTEMPT UNTIL RECTIFIED. But in my eagerness to get her going, I tried a few more cranks and she started and ran right to full speed for a few seconds until I placed a wood plank over the intake throat where the filter screen attaches. Fortunate for me, I had removed the screen and had plank at the ready. She still idled for about a minute before finally suffocating and stopping. During this time the stop lever and speed lever had no effect.


After lots of research online and in the service manual, I first removed the high pressure fuel lines and cranked the engine bit. No fuel from rear injector pump outlet. So I removed and disassembled the pump to confirm my suspicions.... the plunger in the pump was stuck likely due to two year old fuel residue. What was worse, the stuck plunger caused a stuck fuel pin on, which caused a stuck fuel rack... in the full speed position! I had front three cylinders running away with no fuel to number four.


Here's what I have to share...


1. The speed lever (don't call it a throttle) is not directly connected to the fuel rack. It is connected to an adjustment spring on the governor which IS connected to the fuel rack. The speed lever adjusts the target RPM that the governor adjusts the fuel rack, which, turns the fuel pinions which adjust the amount of fuel pushed by the plungers each stroke. The stop lever manually pulls the fuel rack to the no fuel position, BUT... if you push the stop lever back in (assuming you have a manual pull) after it stops, you are returning fuel rack control to the governor, which is trying to get to idle RPM, and thus the fuel rack is in the full fuel position. Maybe if you're going to lay up for a long time, wouldn't it be wise to leave the stop lever pulled to at least have a stuck fuel rack in the stop instead of full speed position?


2. If you're checking out a diesel engine unknown to you, or having been laid up a long time, disconnect the high pressure fuel lines and check fuel delivery by the injector pump and spray out the lines with carb cleaner, and blow dry. Reinstall but leave all injector nuts cracked open until you get fuel seeping from ALL cylinders before tightening ANY.


3. If you have a stuck plunger and don't want to remove for a full teardown, try to get a solvent into the plunger/barrel that's stuck to free it. You may have to gently push the plunger as you turn the shaft to get it to move both ways.


Disclaimer... I realize that the best course of action is to have a profesional remove, service, and test the pump and injectors in a diesel shop. But lots of cruisers find themselves hundreds if not thousands of miles away from professional help, and resort to self help. I was in that situation.

To split hairs a little bit, technically what you experienced wasn't a runaway, but an unexpected excursion to wide open or near wide open throttle position (throttle's not accurate but it's OK to use the term colloquially here).

Scary enough, especially when unexpected, but not really a dangerous situation. Good that you were prepared and got it under control quickly; perhaps my first move would have been to shut off the fuel supply and then block the airflow, though many of us are not known for our cool intellection in such circumstances.

My curiosity would be more picqued as to what the effects of running a four cylinder engine on three cylinders at WOT for a prolonged period would be. Intuitively I'd think that the unbalanced forces generated by the unfueled cylinder would not throw a rod (a perhaps more common result of a runaway) but might break a crank. Luckily the question is moot in this case.

Good job.

As for a 'real' runaway, it's generally caused by an ungoverned source of fuel allowing the engine to rev out of control, which at a certain point literally blows the engine apart. Probably the most common sources, in no particular order, are a ruptured diaphragm-type fuel pump diaphragm, an overfilled crankcase, a broken turbo oil line or severely worn turbo oil seals. With a bad runaway, depending on the engine design, blocking the air intake might not even slow it down; the engine will pull air in through the crankcase ventilation, oil seals, poorly sealed gasketed joints; basically wherever it can.

Luckily these are rare and larger engines are more susceptible.


It is a scary thing; one certainly wouldn't even think of using their hand to try and stop it when experiencing one, doing so on anything over a tiny engine could easily cause serious damage to your skin or worse. No matter what anyone else advises, don't try it on anything larger than a smallish lawn mower type engine.

[Wotname]

Originally Posted by Compass790

...........


Wottie if you check the clearance of a mostly open valve you will see it must contact the piston at TDC.The head is pretty flat & the piston rises fractionally above the liner top.That is, if the decomp lever opens it fully. Guess that is the big question. You would think they'd design it not to hit but....

..................

Let me save you some trouble....
From the YSM8 manual.
Top clearance - 0.6mm (worst case)
Valve recess - 1.25mm

So the valve has to be depressed at least 1.85mm before the piston will hit it. The decompression lift is not adjustable for the YSM so no value is given.

So for more guidance, let's look at the 2QM20 numbers because the decompression lift is adjustable for the 2QM20 (although not adjustable for the 2QM15).

From the 2QM20 manual.

Top clearance - 1.08mm
Valve recess - 1.05mm
Total gap before valve hits piston is 2.13mm

Decompression lift is adjusted to 0.8mm

That leaves at least 1.33mm gap between the decompressed valve and the piston for the 2QM20 engine.

I'll bet you a fishing trip the YSM has a proportionally similar clearance.

Of course your engine might be different as it is somewhat dependant on one's engine rebuilding expertise - sorry

Disclaimer - I ain't a mechanic but I can read the manual .

[Compass790]

Originally Posted by Wotname

Let me save you some trouble....
From the YSM8 manual.
Top clearance - 0.6mm (worst case)
Valve recess - 1.25mm

So the valve has to be depressed at least 1.85mm before the piston will hit it. The decompression lift is not adjustable for the YSM so no value is given.

So for more guidance, let's look at the 2QM20 numbers because the decompression lift is adjustable for the 2QM20 (although not adjustable for the 2QM15).

From the 2QM20 manual.

Top clearance - 1.08mm
Valve recess - 1.05mm
Total gap before valve hits piston is 2.13mm

Decompression lift is adjusted to 0.8mm

That leaves at least 1.33mm gap between the decompressed valve and the piston for the 2QM20 engine.

I'll bet you a fishing trip the YSM has a proportionally similar clearance.

Of course your engine might be different as it is somewhat dependant on one's engine rebuilding expertise - sorry

Disclaimer - I ain't a mechanic but I can read the manual .

Did you read to the btm of the page this time Wottie?
OOOHhh thats an underarm the engine rebuilding expertise crack.


Just looking at the possible depression of the lever in the rocker cover I'd estimate the possible valve lift at 4 to 5mm but that depends on the gap between the rocker arm & the decompression actuating rod flat face.


Its a 10mm rod & half of it is machined flat to sit on or above the rocker arm & its rotated till flat is almost vertical when you turn the decompression lever hence possible 4-5mm lift

Thanks for coming up with the clearance figures, certainly seems possible for valve to hit piston on the YSM8.

Yes you & scubaseas are probably right that Yanmar would make it so v/v doesnt open far enough to hit the piston.
However, I'm not surrendering until I've checked whats happening when I use the decompression lever.
It may be that, as I mentioned earlier, operating the lever with no cable lifts the valve more than designed.
I'm not going to pull the head off to check but if I had a spare exhaust valve I'd check on my spare head.

I'll pass on the fishing trip wager, my debts are mounting

[Dougtiff]

Back in the 80'S, when i was working as a Oilfield Diver, i was assigned to a floating drilling rig, our diving system [think diving bell and decompression chamber, ect.] was adjacent to the engine room, and the very large hatches were open, being we were in the Java sea, Indonesia, it damm hot, and ventilation is needed, anyway, i was doing some work on the diving system, when i heard a load sound starting to come from the engine room, it grew louder very quickly, until it was screaming, and then a sound of the engine blowing up, smoke pouring out of the hatches, then all was quiet, except for all the shouting, for some reason the BIG Cat engine ran away, blowing rod's out the side, i don't know how many horse power that engine was, but in the thousand's I'm sure, it powered the generator that provided the electricity for the drilling rig, and without it, the rig couldn't drill, now the rig had a stand by engine, same size Cat, but the mechanic's had been robbing part's off it, to keep the other engine on line, there was a small gen set for emergency, which kicked it, powering essentials, like communications, freezer's,ect., well all hell broke loose, as the contract starts penalizing the drilling company ater so many day's, if the rig is not drilling [turning to the right,as they say], in lots of Dinero,so lots of head's rolled, we all walked around like on egg shell's for a number of day's, as i recall, it took about a week to get up and running again, part's were being flown in from all parts of the world, as Cat in Peoria didn't have every thing needed, but i'll never forget the sound of that engine running away.

[SobeFlyer]

Originally Posted by jimbunyard

...As for a 'real' runaway, it's generally caused by an ungoverned source of fuel allowing the engine to rev out of control,...

For sake of discussion only, wouldn't my situation with a fuel rack stuck at WOT even if only feeding three cylinders meet your definition of "ungoverned source of fuel" ?