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Author Topic: Runaway Detroit 6-71 - Last night's excitement  (Read 9023 times)
n4rsn
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« Reply #15 on: July 23, 2006, 12:20:19 PM »

But did he have a runaway engine or just a stuck qccellerator or rack? I do not think he ever took it out of gear long enough to find out. Yes theos babies will sound like a runaway if they go up to the governor but it will really not hurt them.
Richard

He said it went to 2450, and was governed to 21, I think, so I wouldn't take a chance. Check the throtle cable in the rear at the govener, If all is ok, go to the rack next.
Steve
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NCbob
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« Reply #16 on: July 23, 2006, 12:51:12 PM »

Fellas, before we start all the panic business about how these Detroit's are subject to runaway...let's calm down and take a good look at not only the evidence of this scenario and the maintenance background of the engine.

Most of these old buses sit for long periods of time doing nothing except for an occasional  startup to keep the owner from feeling guilty.  If they are run, it's generally short trips for about the same purpose.  Engines that are excercised regulary are not susceptable to these types of problems.

Maintenance, the word we hate most for the reason that we're not qualified to run a rack or can't find somone who will do it inexpensively enough to suit our budgets.  Racks and injectors are prone to sticking if not used on a regular basis.  But as Tom pointed out the N or lettered injectors are built slightly different in the the fuel rack of each injector is loaded to go back to the no fuel position.

In this case...Did his engine start consuming it's own oil from the base as an alternative source of fuel?  I think not since he was only down a couple of quarts.

What the other possible source of the problem?  Not too much air for certain.  A stuck rack or one stuck injector which could hold the other 5 in the full fuel position and make the engine uncontrolable in the sense that we normally think of as 'control'.  Would the engine have overspeeded beyond the point of Governor control?  I don't believe we know that yet.

With a Limiting Speed governor the Operator only has control of engine speed at the mid-range. From idle to midrange (low) and from mid-range (High) to No-load RPM the governor is complete control over the engine...unless something is either broken or out of adjustment.  If a cotter pin through the clevis which connects the rack to the Governor operating lever had dropped or vibrated out we could re-construct exactly the same scenario.  But the engine would have gone to full fuel and might have self destructed.
The question really is then...did the governor have control of the engine up to and including No Load RPM?

Obviously the operator was much too busy and concerned about the welfare of his family and the situation at hand to make such a conclusion. Was he headed downhill and thought he observed an overspeed condition beyond no load?

So, logically we will have to adopt a wait and see attitude until a properly trained technician makes a determination as to what happened.

I will repeat a statement I posted some time back.  Detroit Diesel has, for some years recommended the removal of air box dampers.
A properly maintained and adjusted engine will not "run away".  I have removed the air box shut down from my engine so I practice what I preach.  They cause more problems that they ever corrected.

I did not intend for this post to be this long, nor did I intend to represent myself as an "Expert" on Detroit Diesel Engines.  I was trained at Detroit Diesel in Detroit many years ago on both the 53 and the 71 Series.  I've spent almost 30 years running yachts for a living with mostly Detroit Diesels, in pairs, under my feet.  Never, repeat... Never in all those years have I had a problems such as described in this thread.  And I, from time to time, placed a whole lot on the dependability of those engines.  People's lives were the
bottom line...they brought us home every time!

FWIW

Bob
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WEC4104
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« Reply #17 on: July 23, 2006, 12:54:50 PM »

I had my wife play with the throttle pedal while I watched in the back, There didn't seem to be any issue with the cable, linkage or spring return.  I suspect either the fuel injectors / rack, or the engine getting fed a supply of motor oil.

My governor typically limits me to about 2150-2200 rpm.  I saw 2450 driving down the highway on a slight grade.  I used some gentle brake action to get down to 2100 on flat land. As soon as I pressed the clutch in she immediately went over 2400 and I had to quickly let the clutch back out to keep her from climbing further.
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« Reply #18 on: July 23, 2006, 01:08:59 PM »

"My governor typically limits me to about 2150-2200 rpm.  I saw 2450 driving down the highway on a slight grade.  I used some gentle brake action to get down to 2100 on flat land. As soon as I pressed the clutch in she immediately went over 2400 and I had to quickly let the clutch back out to keep her from climbing further."

"Gentle brake action......."  That tells me that you're one cool headed Dude!  You were in control.  For that I offer a tip o' the hat!

My best guess, if we're allowed them, is that you had one or more injuectors stuck in the full fuel position to the point where the governor no longer had control of the engine....which surprises me.  Because the governor is able to exert one helluva lot of pressure on the rack to control engine speed.  Might I caution you to have, whoever checks you engine, to not only find the problem but to compare very carefully the existing fuel rod from your governor with a new one to see if it is bent, even slightly.

Regardless, you're in for a rack run at best and possibly a governor repair at worst.  Probably wouldn't be a bad idea to pull the hand hole covers and check for any damage to the pistons, rings and liners. 

Stay in control, m'friend...you're a guy to go down the road with. Wink

Bob
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n4rsn
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« Reply #19 on: July 23, 2006, 01:11:27 PM »

Bob, I hate to tell you this, but, Here goes.
        As a Detroit Mechanic, Trained by detroit Diesel, in St. Louis, on the 71 series, and the 92 series, I have had 2 seperate 71's to run away, I managed to get 1 stoped, the other broke a blower shaft before it blew its self apart.    Both were caused by a piece of dirt in an injector, jamming the rack in full throtle position.    The one that broke the blower shaft, did not have a working emergancy shut-down.
I would rather reseal my blower, than replace the engine.
Just my 2 cents
Steve
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« Reply #20 on: July 23, 2006, 02:23:37 PM »

Clean Fuel, Clean lube oil, Clean coolant and Clean air with periodic maintenance.

I rest my case.

Bob
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WEC4104
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« Reply #21 on: July 23, 2006, 02:58:58 PM »

While this is all speculation until I get a hold of my mechanic tomorrow,  Maybe we can have some fun with this as a real world situation and everybody gets to play armchair mechanic until I find out and report the final cause.

The facts:

In May, I had a fairly extensive (or is that expensive?) inframe completed by a reputable and knowledgeable establishment.  The inframe included replacing the injectors (N60), cylinders/pistons/etc., and I upgraded the head from a 2 valve to a 4 valve. The blower was also replaced.

Since then I have had two 150-200 mile trips, and one week where I put 700 miles on her. No problems.  My only two concerns were the temp gauge has been running cool (155F) and she seems to be leaking as much, if not more, oil since before the rebuild.  Yes, the proper straight 40 wt oil.  During the 700 mile trip I added a gallon too, and there was some, but not as much, coating the engine exterior.

First hint of a problem was the Turnpike incident Friday evening, until then she was doing great, and certainly running better than before the rebuild.

The injectors are definitely N60s (N65 injectors were in it previously, but she was throwing a lot of smoke under a heavy pedal, and I saw no reason to blast Saudi juice out the tailpipe.)

The oil coating the inside of the engine compartment (radiator side) has me concerned.  Based on what I see on the dipstick, I am guessing I am down more than a gallon in the last 100 miles, not just a few quarts.  She was up near full when I started. When I pulled the stick at the rest stop, she was 1/4 of the way up the stick from the low mark toward the full mark. Granted I had not waited a long time for everything to drain back down into the pan.  

While my wife was following me in her car, she said she noticed some smoking and a smell starting at the same time she saw me start to use the brakes on the turnpike straightaways.  You have to understand that asking her to identify the color of the smoke, or what kind of smell it was, would be pretty futile.

Again, I have no doubt that in neutral or with the clutch depressed, she would quickly rev hundreds of rpms above the governor setting of 2150.  ... and I really don't want to find the upper limit.

So what is everybody's guess? Vote early and vote often.
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JackConrad
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« Reply #22 on: July 23, 2006, 03:50:34 PM »

Ok, here is my guess: Perhaps the smell was your brakes, since you were fighting the engine with them?
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« Reply #23 on: July 23, 2006, 09:07:36 PM »

I doubt if the fire extinguisher idea would work on a 4104 since it has two air intakes.

 I sure wouldn't want to be running around the back from one side to the other with the engine going supersonic.

We had a long discussion about a month ago on the subject of disconnecting the Emerg Shut Off. I think this incident pretty much shows the wisdom of keeping it. There is no way I wll ever disconnect mine and I check it often now. After this, more often!!
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CraigC
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« Reply #24 on: July 23, 2006, 10:06:19 PM »

I could not keep the oil level up to the full mark on my last 2 - 671's. They would be 1/2 way between add marks in about 150 miles. If I would leave them 1/2 way down I would not add any more oil for 4,000 miles or more.

When I had a emergency flap value I would check it's operation to see if it worked on a regular basis.

I found it interesting you went years and did not know if it worked. If it is mechanical and you want it to work someday take nothing for granted. Even with regular maintenance it may not work when needed. Just my opinion.

I vote for a stuck injector.

Good luck getting you bus back on the road!!!! Great keeping your head in a unknown  situation.
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Craig C
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« Reply #25 on: July 24, 2006, 04:05:44 AM »

I vote for stuck rack caused by a defective injector and I also vote for keeping the damper and checking it often to make sure it works correctly.
Richard
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« Reply #26 on: July 24, 2006, 06:48:43 AM »

Craig - I've had the same experience with my 4104 with 6-71.  Mine likes to sit just below 1/2 way, and anything I add above that level exits the engine in short order.  I'm still wondering if I have the wrong (too long) dipstick.

Ok WEC - it's monday.  Any news?
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WEC4104
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« Reply #27 on: July 24, 2006, 09:18:52 AM »

I was in touch with my mechanic this morning and it is looking like my best option is to have her towed. Checking with my insurance carrier, their roadside coverage includes towing "to the nearest qualified repair facility".  I have indicated that my preferred destination is 60 miles away. So far, they have not said "No", but I need to get this confirmed before I give everybody the green light.

That fact that only some towing companies are permitted to tow on the PA Turnpike adds a twist, and I have been in touch with the Turnpike Commission this morning.

Add to this the fact that there are some special requirements for towing a GMC, and it gets more interesting.  I am requesting an under reach style tow with the air line connected from the tow vehicle, etc.  When I started talking about this they put me in touch directly with the towing company. I explained some of this to the dispatcher, who listened for a while, then indicated she would have somebody contact me. Sounds like maybe the towing will be scheduled for tomorrow.

I've had detailed phone conversations with literally eight different people this morning, and am waiting for call backs.  Sure am glad I'm not sitting on the side of the road somewhere.   

A note on the oil level: Prior to the rebuild, I generally kept the level roughly 2/3 to 3/4 full. Trying to keep it at the full line was a waste, as it would drop from Full to 3/4 in the first 200-250 miles.  After that, useage/loss would tend to slow, and I could easily go another 400-500 miles before she would drop below 1/2. Friday night it took me less than 75 miles to take it down to the 1/4 mark.  I'm not ruling out the possibility of the two items being unrelated.

Stay tuned.
« Last Edit: July 24, 2006, 02:32:53 PM by WEC4104 » Logged

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Dallas
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« Reply #28 on: July 24, 2006, 09:52:55 AM »

At the rate you seem to be consuming oil, it sounds like you may have lost a blower seal along with possibly a stuck rack. Be careful whatever you do.

Dallas
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WEC4104
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« Reply #29 on: July 24, 2006, 03:28:02 PM »

Major gymanistics today with my insurance carrier regarding towing.  Initially they agreed to use one towing company and to take it to my preferred mechanic. We only needed to work out the times.  By the afternoon they did an about face and wanted to use a different towing company and started hunting for a closer repair shop. 

Several conference calls, and discussions with supervisors later, it looks like the second towing company will be taking it to my preferred mechanic.   What is really stupid is the amount of time everybody wasted on this exercise. Using my map program, the distance to my mechanic: 61 miles.  Distance to the mechanic they wanted to use: 57 miles.  Arrrggggh.

Eventually it came down to the fact that my guy would take me right away, the other guy couldn't start work for at least a week. I started inquiring about trip interruption coverages on the policy, and loaner vehicles.  That speeded up the answer I wanted.

Busless 72 hours and counting
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