Author Topic: Ok, so talk to me about these engines, the DDs in particular...  (Read 13106 times)

Offline Ed Hackenbruch

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #15 on: June 24, 2013, 05:22:57 AM »
There are a lot of older buses running around out there that you never hear about unless they have a major problem. Seems like that happens to 2 or 3 a year maybe, but it gets everyones attention at the time. :)
Used to own a 1968 MCI 5A with 8V71 and Allison MT644 transmission.

Offline luvrbus

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #16 on: June 24, 2013, 05:51:24 AM »
Most of the time the engines fail because of bad work done down the line by people that have no idea what they were doing that is the case with one in my shop right now 50,000 miles since a out of frame it is a mess for $$$$$  

No more miles than people drive a conversion a fresh engine should last for ever unless driver error cause a problem along with poor maintenance which is another problem  

The one on the board getting all the posts and attention that is the first time I ever saw that happen here on the board it happens to people everyday you repair it and go on  

And to me hoping not to start a war it has done more harm than good for people looking to sell or buy a older bus it is probably why you are asking questions lol JMO

good luck
« Last Edit: June 24, 2013, 05:58:41 AM by luvrbus »
Life is short drink the good wine first

Offline Geom

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #17 on: June 24, 2013, 07:56:31 AM »
Thanks for the info luvrbus. Good to know that a lot of it can be avoided with good maintenance and inspection by qualified experts.

And not wanting to start or perpetuate a war either (as there's really nothing to war about, as it's just the sharing of information), but the situation with Chris and Cherie has been an invaluable source of information. While yes it has been a reality check as to what can happen, it hasn't changed this new perspective buyer's opinion much. It did, however, get me to look more into this decision and what would be involved in doing it right. As has been stated prior, this is not necessarily for the faint of heart or the uninformed. And the more information and knowledge I can gather, the more informed of a decision I can make.

But my question wasn't rooted in just that specific situation, but over dozens of previous posts about major failures caused by this or that; including a few waaay back in the archives about a runaway diesel. That is something I hadn't at all considered, but after thinking of the physics of how a diesel (especially a 2 stroke with possible turbo) works, it makes perfect sense as a possibility and has given me some things to think about and how I could/might manage such an event (and what that ominous looking big red button is all about :) ).

 But this is a board for helping people with those very issues, so it's naturally going to be skewed towards problems. Not a lot of people are going to post a help request to "help me cope with how awesome my ride is", and I get that. :)

But through those unfortunate experiences (that others are fortunately and graciously willing to share), I can expand my sphere of knowledge and understanding. And I would bet a lot more people will be paying close attention to that most humble of items, the oft ignored and out of mind air filter, with a little more scrutiny; which is good :)

Thanks all again for all the advice!
1966 GM 4107
6v92 Turbo
V730

Offline luvrbus

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #18 on: June 24, 2013, 08:24:09 AM »
That red button will not stop a run away you won't find that button on a 92 series or the very late 71 series  lol it is there because on the old type 2 screw non spring loaded fuel rod if a injector stuck in the fuel position that was the way DD designed to the engine to shut it down with the new style fuel rods (spring loaded) it is useless  

I toss that mess it's nothing but problems for owners the shaft wears out the housing the seals go bad and let air pass without being filtered doesn't take a long period of time to dust one leaking there    

good luck  
« Last Edit: June 24, 2013, 08:36:04 AM by luvrbus »
Life is short drink the good wine first

Offline Geom

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #19 on: June 24, 2013, 08:31:22 AM »
That red button will not stop a run away lol it is there because on the old type 2 screw non spring loaded fuel rod if a injector stuck in the fuel position that was the way DD designed to the engine to shut it down with the new style fuel rods (spring loaded) I toss that mess it's nothing but problems for owners

good luck 


Ahh, ok. I get it.

I thought I read somewhere that the (or more appropriately 'a') big red button was for a damper valve that came down and closed off air intake to the blower. So does such an item exist on these engines, or does it depend on what the PO did with it?

Lacking such a device, what can one do (if anything) in such a scenario?
1966 GM 4107
6v92 Turbo
V730

Offline azdieselman

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #20 on: June 24, 2013, 09:42:55 AM »
When you pull the valve covers, You will find all injectors in the full fuel position. This is normal. All the injectors on each bank are controlled by a rack. If 1 injector sticks in the full fuel position, They all stay in the full fuel position, The governor will try to move them outward toward the no fuel position, But it won't have enough force. Shutting off the air is the easiest way to stop the engine, But it will create a high vacuum in the blower and can damage the oil seals, Allowing engine lube oil into the air stream and into the combustion chamber where it burns as fuel.This is where you will have a runaway. A vise grip on each rack will give you the leverage to control the rack with the engine running. You can move the racks by hand with the engine off, They won't move far with the governor lever in the shutdown position, But you will be able to see and feel each injector move. Check both sides, If they all move, Have someone else start it while you stand by with your vise grip already installed. Don't have your hand on it, As it will move when the engine starts. If all is good and you have governor control, Shut it down. Put the valve covers back on and continue with your inspection.
1980 Mod 10

Offline Debo

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #21 on: June 24, 2013, 10:39:08 AM »
Hi Geom,

Most of the time, diesels are cut off by a fuel lever that stops fuel flow. (You may already know this.) I have the emergency flapper valve like you're talking about on my intake to stop a "runaway" engine. It's not something you want to activate unless there's an actual emergency, because it creates extreme suction that can damage the blower seals, etc. It simply cuts off the air to the engine if it's running away and combustion stops. I test mine with the engine stopped.

Other strategies for stopping a runaway include using a CO2 fire extinguisher in the intake to smother engine combustion, or if it's a manual transmission, putting it into a high gear and letting out the clutch with the brake on - obviously things you only want to do in an emergency. It's important to get a runaway stopped if possible though because it's possible that it will accelerate to the point of self-destruction.
1981 MCI MC9
Detroit 8V-71N
Spicer 4-Speed Manual
Outer Banks, NC (Nags Head)

Offline luvrbus

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #22 on: June 24, 2013, 11:12:34 AM »
Ok guy enlighten me were does DD tell you that air shut off is to stop a runaway engine and how do you test the shut down with a engine not running DD tells you to idle the engine and set the shutdown to test ,no way is going to hurt the blower seals at idle  
« Last Edit: June 24, 2013, 05:04:09 PM by luvrbus »
Life is short drink the good wine first

Offline Debo

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #23 on: June 24, 2013, 11:57:07 AM »
LOL. OK. DD doesn't say it's to stop a runaway engine, but my MCI documentation says it will stop the engine if the master switch fails to do so. Maybe an incorrect assumption on my part, but if I'm wrong, I have no doubt that someone here will step in to correct me. I have to think though that if a diesel runs on air and fuel, that cutting off one of those can't hurt to at least slow it down a little. Better than standing there with your hands in your pockets.

It's good to hear that I can test the shutoff at idle. All of the information I gathered here led me to believe that it would damage the blower seals. (If you don't believe me, search for it in the archives.) After testing it with the engine running once, I always just tested the flapper to make sure it would close if I flipped the switch. Now I can really test it again. Awesome.

Jeeze... just trying to help a guy out. Deep breaths...



1981 MCI MC9
Detroit 8V-71N
Spicer 4-Speed Manual
Outer Banks, NC (Nags Head)

Offline luvrbus

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #24 on: June 24, 2013, 12:11:17 PM »
I am sorry if I seemed a short Debo but in 50 years I never saw a runway DD  I saw some get a little wild with people adjusting the Jake buffer that have no idea what they doing or one go crazy from oil build up from a lot of idling but never a full blown runaway 

I read the stuff about never use the air shut it will suck the seals out where that came from only they know I don't

good luck
Life is short drink the good wine first

Offline TomC

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #25 on: June 24, 2013, 01:07:58 PM »
When I had the turbo installed, Don Fairchild took off the emergency flapper valve. The old switch was changed to on/off and wiring I used to power my radiator misters. Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline Dave5Cs

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #26 on: June 24, 2013, 06:02:05 PM »
Tom that's a good idea. I was wondering where I would put that switch. Now I will have to paint the switch cover Aqua Marine. :o

Dave5Cs
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Offline chuckd

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #27 on: June 24, 2013, 06:12:04 PM »
Mine was converted to the macerator switch - not making this up.  Now a switch in the cockpit that turns the pooper shooter on and off is not the most convenient to say the least.

Chucked
Stillwater MN
1979 Prevost

Offline Geom

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #28 on: June 24, 2013, 06:13:48 PM »
So is it fair to assume that a real runaway is usually the product of prolonged neglect/abuse and not a likely/plausible event on a running and otherwise maintained engine?

@Debo, I had considered the CO2 extinguisher. Might not be a bad thing to keep close to the engine bay regardless. Is the air intake generally accessible enough to shove CO2 into (if the unlikely happens) or will I simply just be coating it white as it finishes ripping itself apart :)

I also assume that killing the normal source of fuel is not enough to stop a real runaway, as it's moved on to ingesting its own oil?
1966 GM 4107
6v92 Turbo
V730

Offline luvrbus

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Re: Ok, so talk to me about these engines, the DDs in particular...
« Reply #29 on: June 24, 2013, 06:20:08 PM »
I would worry about something else besides a runaway engine ??? with a 50 year bus that should be the least of worries
Life is short drink the good wine first