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Old 07-27-2016, 03:36 PM   #11
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Good plan. I am working on an emergency shutdown device for my little 4BT. Personally, I think every diesel should come equipped with one. I am actually considering an RV blackwater dump valve on the air intake side of the turbo. The "real deals" work just the same...they just cost about $600 bucks more.
Too funny!

I tried one on an 8v71 but it was too small and restricted the intake. On a 4BT it should work fine.

Make sure you keep it lubricated and cycle it open & closed periodically. If left unattended they tend to stick....
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Old 07-27-2016, 03:40 PM   #12
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I love how this discussion has gone to the crapper...
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Old 07-27-2016, 10:28 PM   #13
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Originally Posted by Tango View Post
Good plan. I am working on an emergency shutdown device for my little 4BT. Personally, I think every diesel should come equipped with one. I am actually considering an RV blackwater dump valve on the air intake side of the turbo. The "real deals" work just the same...they just cost about $600 bucks more.
I've also been thinking about making one, even though my engine's a DDEC so it doesn't have racks to stick open like on a MUI. I'm thinking of a CO2 injection system, using a CO2 extinguisher to discharge directly into the intake. I saw a video on YouTube of someone stopping an 8V71 this way, but it wasn't a run away - I guess as long as you reduce the oxygen level in the intake to less than supports combustion, then it should work?

Wouldn't you hydrolock an engine if you injected a liquid (even a chunky liquid) into it? And don't stand behind the exhaust, otherwise you'd be pelted with superheated turds - imagine if you had to go to the ER with 3rd degree burns and bruises to your lower legs caused by this?

John
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Old 07-28-2016, 09:14 AM   #14
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Diesel newbies are often unaware of just how simple these engines are to keep running. Once in motion, all they need is fuel & oxygen. Compression provides the ignition source.

And therein lies the danger.

Remember...when you turn a key to "shut down" one of these, all that takes place is that a solenoid closes off the primary fuel supply. Notice I said "primary". Give it any source of fuel and it will happily run on regardless of what position the key is in. And with enough of a supply, it will rev up to and well beyond it's limit resulting in a very big Kablooey.

So...where else can a diesel find another source of fuel?

First suspect is usually a failed fuel solenoid. You turn off the key and if that solenoid is bad...the fuel just keeps flowing. Good news there is it will often be limited to an "Idle" flow and stay at that RPM. But not always.

Another source of fuel is...the engines motor oil. Remember...Herr Diesel's motors were originally called "Oil Engines" and can run on darn near anything. Badly leaking rings can actually allow enough oil up into the cylinders for the motor to rev up until it either blows up or has consumed all the oil in the pan. Either way, the results are expensive.

One more source of engine oil being introduced into the cylinders is through a turbocharger. They all have a high flow supply line that feeds their bearings. Worn, sloppy bearings can also leak enough motor oil to feed the beast and cause it to go wild.

Any other sources for fuel? Yes. A diesel will run on anything combustible that is in the atmosphere/air supply. Every diesel power plant/engine in Oil Patch is required to have some means of shutting off it's air supply for just this reason. It is quite common for fairly high levels of methane/natural gas to be present in the air around drilling rigs and these engines will suck it in and run away unless that fuel supply is quickly and completely cut off. You do not want to be anywhere near an 1100 cubic inch, 16 cylinder diesel when it explodes. Or a 4 cylinder for that matter.

Given that they can run like gangbusters on their own oil or anything else combustible that can find it's way into the cylinders...the only proven way to prevent a diesel from running away is to shut off it's air supply.

Long story short...a mechanism for controlling the engines air/oxygen supply is a really good idea. Particularly for older, high mileage engines.
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Old 07-28-2016, 01:05 PM   #15
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Wow, Tango. If I had never driven diesels, I'd probably go nowhere near them.
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Old 07-28-2016, 03:00 PM   #16
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While in the USCG I was working on a 6-71 & needed to rotate the crank a couple of degrees.Without thinking I hit the start button & the engine started and ran for a couple of seconds.What is really interesting is that the jumper lines were off and at least 2 of the injectors had been removed.Only damage was to my underwear.

On a serious note, make sure the injectors are in good shape.You donít want to blow a tip off.That will cause serious damage.

Air shut down: Detroit has a flapper assembly that will shut down air to the blower. Easy to install and remotely trigger. Make sure it has the proper gaskets or it wonít seal and not stop the engine. Checking it on a regular basis is sound advice. Donít do it with the engine running other than when doing the initial test very often or it can lead to blower seal failure.
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Old 07-28-2016, 03:20 PM   #17
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Don't get me wrong. I LOVE diesel engines. But like anything mechanical, they require some basic understanding to live happily with and I have been surprised by how many folks are not at all familiar with the "run on" or "run away" potential they can be subject to.

BTW...there are tons of YouTube vids these days of such catastrophic failures. Most seem to occur on backyard transplants and home rebuilds.

One more caution...

Never attempt to shut off the air on a running diesel by covering an open turbo with your hand. I know, it sounds like a common sense thing, but hey...how common is common sense these days? More than a few fingers and hands have been sucked into those very high RPM turbo vanes. A turbo spins fast. Very fast. Most peak between 80,000 and 150,000 rpm and low inertia turbos can hit over 190,000 rpm. It ain't pretty and your digits won't even slow the motor down. Not a good idea to try and stuff a rag in there either. Something like a flat board or clipboard might work but only with caution. Remember...a diesel runs at MUCH higher compression and combined with a turbo typically produces a much higher vacuum at the intake.

Be informed. Be safe.
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Old 07-28-2016, 05:02 PM   #18
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Originally Posted by Tango View Post
Don't get me wrong. I LOVE diesel engines. But like anything mechanical, they require some basic understanding to live happily with and I have been surprised by how many folks are not at all familiar with the "run on" or "run away" potential they can be subject to.

BTW...there are tons of YouTube vids these days of such catastrophic failures. Most seem to occur on backyard transplants and home rebuilds.

One more caution...

Never attempt to shut off the air on a running diesel by covering an open turbo with your hand. I know, it sounds like a common sense thing, but hey...how common is common sense these days? More than a few fingers and hands have been sucked into those very high RPM turbo vanes. A turbo spins fast. Very fast. Most peak between 80,000 and 150,000 rpm and low inertia turbos can hit over 190,000 rpm. It ain't pretty and your digits won't even slow the motor down. Not a good idea to try and stuff a rag in there either. Something like a flat board or clipboard might work but only with caution. Remember...a diesel runs at MUCH higher compression and combined with a turbo typically produces a much higher vacuum at the intake.

Be informed. Be safe.
Completely agreed! Diesels are a different animal from petrol engines. Basic maintenance and care can be accomplished by most skoolie owners. Serious work requires some smarts, attention to detail and often heavier tools. People really should think twice before digging into their diesels.
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Old 08-24-2016, 02:20 PM   #19
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Well damn. Despite the direction the thread has run away in, I'm grateful for the advice and warnings. Unintelligently of me, I didn't check this post before I started the bus and ran it 30 miles down a mountain, but it did just fine and didn't try to kill me. Granted, it only has 103XXX on it, but it did sit for 5 years, so I'll probably be installing an air shut off valve in the very near future. On that note, two more questions. 1. With such few original miles on the motor, but also considering sitting for 5 years out of service, what is the danger of seals degrading so badly that a run away is possible? 2. Is a 6N71 a dry or a wet sleeve motor, which coolant should I use for it, and are there any fancy rules or tricks to flushing and changing the coolant?
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Old 08-27-2016, 09:28 PM   #20
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Well damn. Despite the direction the thread has run away in, I'm grateful for the advice and warnings. Unintelligently of me, I didn't check this post before I started the bus and ran it 30 miles down a mountain, but it did just fine and didn't try to kill me. Granted, it only has 103XXX on it, but it did sit for 5 years, so I'll probably be installing an air shut off valve in the very near future. On that note, two more questions. 1. With such few original miles on the motor, but also considering sitting for 5 years out of service, what is the danger of seals degrading so badly that a run away is possible? 2. Is a 6N71 a dry or a wet sleeve motor, which coolant should I use for it, and are there any fancy rules or tricks to flushing and changing the coolant?

I don't really know with any certainty if the sitting time would have degraded the seals enough to be an issue. All of the runaway's I have heard of occurred with high mileage motors or on motors that had been sitting for some time. On the latter the runaway occurred on the initial startup.

I have driven a number of 2 stroke Detroits that had been stored for some time and really only worried much about runaway when we first ran them up.

All of the 2 stroke Detroits are wet sleeve.

No tricks. Drain, flush with good water, drain then fill with coolant that meets Detroit's specs. If you mix 50/50 with water use RO or distilled water.
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