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Old 05-03-2014, 21:38   #1
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How do you stop a Diesel Motor

Recently i was on a boat and had to stop the motor, but pulling the stop didn't work, we then tracked the cable and tried manually all to no avail, we phoned a "friend" he suggested pulling off the air filter cover and starve it of air this may have worked if we had gear with us to do it.

the boat had trouble going into and out of gear so stopping the engine was called for, and we did not want to sit and wait for the fuel to run out then bleed the engine to make it run again if we were to turn off the fuel lines

i have never run across this issue before and wondered if there is a way to kill the motor quickly
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Old 05-03-2014, 21:47   #2
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Re: How do you stop a Diesel Motor

Diesels require 3 things to run…
AIR
FUEL
COMPRESSION

Remove one of these and the motor will stop!
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Old 05-03-2014, 22:15   #3
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Re: How do you stop a Diesel Motor

Blocking the air intake cover would be my move. At least with my Yanmar 3gm, I could just smother the air intake cover with a rag rather than take it off and risk any material getting sucked past the filter.

Blocking fuel intake is no guarantee in the event of oil runaway and loss of compression via a rag seems the least desirable of the three ways to shut things down

I am yet to be paid for diesel work though so this is not religion

Boat Rat: Killing the Runaway Diesel | Cruising Compass ? The Free Weekly Newsletter for Sailors & Cruisers ? ©2013 Blue Water Sailing
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Old 05-03-2014, 22:31   #4
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Re: How do you stop a Diesel Motor

Quote:
Originally Posted by 40 South View Post
Diesels require 3 things to run…
AIR
FUEL
COMPRESSION

Remove one of these and the motor will stop!
FUEL
Ok We never wanted to have to bleed the motor (although this is what we did)
by turning off the fuel supply, in low revs it took maybe 4-5 minutes for it to stop (too long in our situation)

Air
We tried a few rags but couldn't get it to stop or even show signs of stopping, how long does this method usually take

Compression
How does this work when the motor is running? what do you do to loose compression?


I just thought maybe there was a quick way without us having to bleed a hot motor in very confined space
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Old 05-03-2014, 22:33   #5
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Re: How do you stop a Diesel Motor

There is a difference between a runaway diesel and an non operative stop cable or button. Do you know what you had? It sounds like you had a runaway, but you make no mention of the horrible noise and billowing black smoke of a usual runaway. If the motor was responding to normal throttle settings and idle, you had a faulty stop solenoid or cable. World of difference. The only way to stop an actual runaway is to stop the air intake, since the engine is running on crankcase oil, diluted from leaked diesel, not from the normal fuel injection. If the engine responds to normal throttle control and you still cant shut it down, then take the correct size wrench, or and adjustable spanner and loosen each injector nut until the engine stops. You will have to bleed the injectors to get it running again, but at least it will stop. There are many threads on CF about bleeding diesels. Good Luck. _____Grant.
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Old 05-03-2014, 22:35   #6
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Re: How do you stop a Diesel Motor

Quote:
Originally Posted by laika View Post
Blocking the air intake cover would be my move. At least with my Yanmar 3gm, I could just smother the air intake cover with a rag rather than take it off and risk any material getting sucked past the filter.

Blocking fuel intake is no guarantee in the event of oil runaway and loss of compression via a rag seems the least desirable of the three ways to shut things down

I am yet to be paid for diesel work though so this is not religion

Boat Rat: Killing the Runaway Diesel | Cruising Compass ? The Free Weekly Newsletter for Sailors & Cruisers ? ©2013 Blue Water Sailing
Yeah we tried this for a couple of minutes maybe we were not completely blocking the intake sufficiently but couldn't get it to even show signs of it slowing
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Old 05-03-2014, 22:44   #7
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Re: How do you stop a Diesel Motor

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Originally Posted by gjordan View Post
There is a difference between a runaway diesel and an non operative stop cable or button. Do you know what you had? It sounds like you had a runaway, but you make no mention of the horrible noise and billowing black smoke of a usual runaway. If the motor was responding to normal throttle settings and idle, you had a faulty stop solenoid or cable. World of difference. The only way to stop an actual runaway is to stop the air intake, since the engine is running on crankcase oil, diluted from leaked diesel, not from the normal fuel injection. If the engine responds to normal throttle control and you still cant shut it down, then take the correct size wrench, or and adjustable spanner and loosen each injector nut until the engine stops. You will have to bleed the injectors to get it running again, but at least it will stop. There are many threads on CF about bleeding diesels. Good Luck. _____Grant.
Sorry the motor was operating normally we had an issue with the stop cable and then manually trying the stop. (we had a gearbox issue in that a selector jammed and we had to stop the motor to move it from reverse to neutral then to forward) hence the need to stop it quickly while trying to manoeuvre in a marina

in the end we used sails, but for future i was asking to see if we could have stopped the motor quickly, given the normal stopping method had failed to work
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Old 05-03-2014, 22:47   #8
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Re: How do you stop a Diesel Motor

Quote:
Originally Posted by aclmck View Post
FUEL
Ok We never wanted to have to bleed the motor (although this is what we did)
by turning off the fuel supply, in low revs it took maybe 4-5 minutes for it to stop (too long in our situation)

Air
We tried a few rags but couldn't get it to stop or even show signs of stopping, how long does this method usually take

Compression
How does this work when the motor is running? what do you do to loose compression?


I just thought maybe there was a quick way without us having to bleed a hot motor in very confined space
FUEL:
Your shutdown cable (or solenoid) should be connected to a lever to stop the fuel at the fuel pump on the motor. Activating this by hand should stop the motor instantly so long as it is not running on crankcase oil (runaway). If it is a modern common rail motor then cutting electricity will stop the injectors from opening = no fuel. Shutting the fuel at the tank can take some time as there is still fuel in the filters and lines, as you found out.

AIR:
Block the air intake with solid object, NOT HANDS as injury may occur because of suction. e.g. a board across the intake. Not rags as they still allow air to be sucked in. Not soft items as there is a real risk of them being sucked into the motor. The seal has to be good. Should stop within a few revolutions. I have stopped a Detroit 6-71 using the air flap in the intake. It took a couple of revolutions to stop.

COMPRESSION:
Some small diesels are fitted with decompression levers. Open these and the motor will stop instantly.

Hope this helps
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Old 05-03-2014, 23:07   #9
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Re: How do you stop a Diesel Motor

Quote:
Originally Posted by 40 South View Post
FUEL:
Your shutdown cable (or solenoid) should be connected to a lever to stop the fuel at the fuel pump on the motor. Activating this by hand should stop the motor instantly so long as it is not running on crankcase oil (runaway). If it is a modern common rail motor then cutting electricity will stop the injectors from opening = no fuel. Shutting the fuel at the tank can take some time as there is still fuel in the filters and lines, as you found out.

AIR:
Block the air intake with solid object, NOT HANDS as injury may occur because of suction. e.g. a board across the intake. Not rags as they still allow air to be sucked in. Not soft items as there is a real risk of them being sucked into the motor. The seal has to be good. Should stop within a few revolutions. I have stopped a Detroit 6-71 using the air flap in the intake. It took a couple of revolutions to stop.

COMPRESSION:
Some small diesels are fitted with decompression levers. Open these and the motor will stop instantly.

Hope this helps
although we tried some of these we didn't try the complete blocking of the air (we had not enough tools to remove the rest of the gear) we had thought that rags would have worked.

We Had an old clunker but it did have decompression levers which when activated failed to work (or at least in 30-60 seconds)

to be honest we never tried to stop the fuel at the motor like that as it was difficult to get to the injectors with the motor running and hot
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Old 05-03-2014, 23:22   #10
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Re: How do you stop a Diesel Motor

Having had runaways on both boat diesels and old tractors, I would say dont ever use a rag to try to stop a runaway. The rag can easily be sucked into the engine and bend a valve, which requires major engine work. What I have done is to use a piece of wood (2 by 4 or 2 by 6) that is pushed against the manifold where the air filter was removed from. A hard cover book will work, not your hand. Most runaways dont damage the engine unless it goes on for a long time. After the first runaway on my boat diesel (really scary) I always left the air filter just loose enough to be lifted off easily. Another 2 cents worth of advice. ____Grant.
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Old 05-03-2014, 23:23   #11
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Re: How do you stop a Diesel Motor

I have tested diesel emergency stops many times. They always involve shutting off the air.

You can use a flat strong board.


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Old 05-03-2014, 23:25   #12
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Re: How do you stop a Diesel Motor

I don't imagine they're still legal, but the engineer of an under-maintained large sailing vessel which I will not name used to keep an aerosol can of BCF (extinguisher, aka Halon IIRC) handy to the intake of each engine. Big engines can kill when they overspeed and self destruct.

CO2 works just as quickly (although its a long time since I saw a sparklets bulb, or a soda siphon) but the dry powder type, especially, is not good for the engine.

Better for the ozone layer, though, and it still saves lives in the engineroom, so it gets my vote....

On small boats, it's a good idea to have a small port with a hanging swinging "lens cap" like in prison doors, in a bulkhead or sidewall of the engine room. That way you don't have to open an access door if the engine goes on fire (or overspeeds), you can just hold your extinguisher up to the aperture and 'fill your boots'
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Old 05-03-2014, 23:37   #13
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Re: How do you stop a Diesel Motor

Andrew, many years ago I was told that spraying CO2 into a running motor would cause broken pistons because of the freezing effect of CO2 against the almost red hot pistons. Maybe it is a myth, but it sounds logical. I think some way of shutting off the air is the only safe way to shut down a runaway. Maybe I need to relearn. ____Grant.
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Old 06-03-2014, 00:07   #14
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Re: How do you stop a Diesel Motor

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Andrew, many years ago I was told that spraying CO2 into a running motor would cause broken pistons because of the freezing effect of CO2 against the almost red hot pistons. Maybe it is a myth, but it sounds logical. I think some way of shutting off the air is the only safe way to shut down a runaway. Maybe I need to relearn. ____Grant.
If I was an engineer whose owner refused to make the engines safe, I would consider that a point in favour!

If I had to do it to my own boat or a friend's, I would simply hold the soda siphon (with no water payload, of course) further away, so the CO2 was roughly at ambient temperature by the time it displaced all the air in the vicinity of the intake.

But, as I think I implied, BCF was always considered to be better for the engine.
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Old 06-03-2014, 03:39   #15
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Re: How do you stop a Diesel Motor

Thats fine guys but as i said above i didn't have a runaway, i had a broken stop mechanism, so i don't see how this is connected????
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