swingin' boss.
another source .. price doesnt break the budget either. maybe tho, this is just the "innards"?
Last edited:
Scenicruisin'..?
- Thread starter amazinblue82
- Start date
another source .. price doesnt break the budget either. maybe tho, this is just the "innards"?
azblackhemi
Old Man with a Hat
Pricey little devil but they have one in stock it says.
Chris, I didn't get a price quote .. the ebay part number was $25.00. What did you find out?
azblackhemi
Old Man with a Hat
Much much much more reasonable!
azblackhemi
Old Man with a Hat
The page said $402! LOL.
azblackhemi
Old Man with a Hat
Kevin .. honestly I was having heart palpitations at the time.
I wanted my friend to flip the cut off switch a bit faster cuz I just wanted to get outta there. I had visions of the authorities trying to explain to my kids how come my chest was missing.
I exaggerate the actual situation but NOT my pounding pulse.
Check out 8:50 to about 9:30 from Bus Grease Monkey (even HE had that " fight or flight" moment - he does a "exciting" post mortem from about 10:10 for a couple minutes to the end).
This runaway event did NOT happen to me, but I worried it would suddenly get all WOT on me.
I was stooped under the rear hatch, trying to keep my wits about me while looking for "click-hiss" source. My recollection is clouded by the anxiety of the moment.
Again it was just idling, but my face was a foot away from it. Not a comfortable place for me. It was loud but not "ear plug" kinda loud.
Anyway, I think the shut-off lever moved less than an 1/2 inch clockwise when the bus shut off.
I don't think the cylinder shaft budged at all after I manually moved the shut off lever. It was not touching the lever when I had my left hand on the cylinder .. that's where I thought the air leak was because I felt it.
The cylinder would click, polished shaft would extend maybe 1/4 inch, the shaft touched the shut off lever but NOT move it, hissed air, then I don't think the polished shaft moved backward (back into the cylinder body) too much?
I watched that cycle twice, saw what the cylinder shaft wanted to do, before moving the shut off lever clockwise with my right hand.
twostick
Senior Member
Kevin .. honestly I was having heart palpitations at the time.
I wanted my friend to flip the cut off switch a bit faster cuz I just wanted to get outta there. I had visions of the authorities trying to explain to my kids how come my chest was missing.
I exaggerate the actual situation but NOT my pounding pulse.
Check out 8:50 to about 9:30 from Bus Grease Monkey (even HE had that " fight or flight" moment - he does a "exciting" post mortem from about 10:10 for a couple minutes to the end).
This runaway event did NOT happen to me, but I worried it would suddenly get all WOT on me.
I was stooped under the rear hatch, trying to keep my wits about me while looking for "click-hiss" source. My recollection is clouded by the anxiety of the moment.
Again it was just idling, but my face was a foot away from it. Not a comfortable place for me. It was loud but not "ear plug" kinda loud.
Anyway, I think the shut-off lever moved less than an 1/2 inch clockwise when the bus shut off.
I don't think the cylinder shaft budged at all after I manually moved the shut off lever. It was not touching the lever when I had my left hand on the cylinder .. that's where I thought the air leak was because I felt it.
The cylinder would click, polished shaft would extend maybe 1/4 inch, the shaft touched the shut off lever but NOT move it, hissed air, then I don't think the polished shaft moved backward (back into the cylinder body) too much?
I watched that cycle twice, saw what the cylinder shaft wanted to do, before moving the shut off lever clockwise with my right hand.
I'd say it's a safe bet the cylinder is your problem.
I've been as close as you were standing to one in full runaway mode. I was young and dumb at the time and it didn't hit me until after I had it shut down how badly that could have ended.
Kevin
thethee
Senior Member
Well at least now you know how to manually shut it off. And in the unlikely event that you DO have a runaway situation it's the same procedure.
If you pull the plunger with your hand, can it extend further? Is it easy to operate? Could it just be binding somehow?
If you pull the plunger with your hand, can it extend further? Is it easy to operate? Could it just be binding somehow?
twostick
Senior Member
A runaway on a 2 stroke Detroit is usually caused by a seized injector or inhaling engine oil through the supercharger shaft seals.
The emergency shutdown in that case involves tripping a butterfly in the air intake elbow on top of the supercharger. When the tach is swinging past 4000 RPM is usually the time you discover the cable is broken or the butterfly is seized on its shaft...
Kevin
Thanks guys. Appreciate your inputs/inquiries.
my comments in RED
sources: Here's How You Quickly Stop a Runaway Diesel
My "problem" was not a "runaway" of course .. I think those are best left to a professional, or someone who knows exactly what to do IF things go sideways. That aint me .. yet or probably ever, but I can be better prepared before getting out there with these buses.
Surely without air it wont run. Not obvious to me what you do to kill the air .. even if you killed the fuel, it could still try to drink the engine oil
I think the issue is UNTIL/IF you choke it of air, its SCREAMING like a banshee, likely OVER-REVVING beyond its mechanical limits at the same time. How long can it run like that BEFORE it grenades -- through the block and/or the supercharger catastophically -- and of course before it can't breathe?
Best case that may only be a few minutes at most.
4501 sat for 20 years inside and didn't run. It went straight to the HD truck guy. I am sure he did/tried stuff BEFORE he started it. Ran it off the "jug", checked injectors first, etc, inspected existing/jerry-rigged air shut off methods, knew what to do just in case.
Me?
I had visions of those pics/vids (the vid was a "staged" event to show what could happen at the end .. the guy started the old Jimmy and ran for his life, and then stood 50 yards away behind a shipping container. better than getting a connecting rod through the face I guess).
Unlikely event in my case with 4903 (it was a running, well-maintained, country-crossing coach when I got it, purrs like a kitten, hardly smokes), , but it IS 56 years old and sh*t happens with old stuff.
My goal is get professionals to take care of them, and yes, see IF something goes bad are there "automated" ways to kill the air -- FAST -- with the flick of the switch before getting distance from the bus and calling the FD.
Last edited:
thethee
Senior Member
Well, yes, an explosion does stop the runaway haha
70NEWYORKER
Well-Known Member
The air-over shut off is nice, but I'd have a cable backup too.....
I was taught in diesel tech a number of years ago that when working on a Detroit Diesel to always have thick block of wood, a piece of plywood or in my case at school a hard bound text book available as a backup to starve the intake air. The teacher reminded us that there was a blower screaming on top, so make sure it was something big. Throw it on the intake and get the hell away. Either it will block the air to starve the oxygen or suck it into the blower. You don’t want to be standing around when the blower tries to chew up the object.
The first diesel engine I rebuilt was 691 backwards bus engine. I did not need the book to stop it.
The first diesel engine I rebuilt was 691 backwards bus engine. I did not need the book to stop it.
New information.
I am a "lurker" member of a couple bus forums. I researched one of them for DD "runaways".
I included a two-page thread link below that took me 30 mins to slog through because I had to keep looking up terms the posters were using.
Detroit Diesel Emergency Shutdown Dampers
The essence of the thread was this:
1. OP was commenting -- politely -- on other members' reactions to something posted about "Emergency Stop" switch on the bus dash.
2. The ES "system" on these old DD's actuates a damper system above the supercharger to shut off the air.
3. The OP had this ES system "disabled" on his DD because a GM "service bulletin(s)" said to do this. Why? Because the ES dampers' activation MAY cause the "blower seals to invert" making the engine start ingesting engine oil. That potential "drinking" its own oil event, even if runaway detonation is ultimately averted by air denial dampers, requires an engine overhaul afterward.
4. You can then imagine the "camps" staking out in other related threads (not posted above). "WhyTF would you disable the anti-runaway system", "cuz they said so", "BS, WhyTF would they do that?", etc. and so forth. This one ended with polite, mildly-debated suggestions but NO consensus and did not produce an authoritative document FROM GM.
Shot of my 4903 dash. The far left switch activates the shut-off cylinder (the leaking part) in my bus
I have better background now to discuss the issue. I did NOT, again, have a "runaway". I had/have a FEAR of one.
They are rare, it seems, in well-maintained DD's but oh my, you gotta have a way to deny a DD air in an emergency.
I gotta try to untangle this alleged "service bulletin" thing on two-stroke, blown DD'S.
GM designs an emergency, damper-based, (right where @twostick said you need it) air shutoff system, for a known but rare (but because its catastrophic in effect - basic FMEA principles) risk they encountered in design and testing, then tells people to disable it?? If true, in favor of what alternative in an runaway emergency??
Something aint hanging together yet.
This is where I get to meet the Bus Grease Monkey, ask the Whisperer when he gets back, and my guys helping me with these coaches.
Going in my "bias" is to do what the bus/diesel engine designer/builders had in mind. Yeah its old hardware, but thought went into these machines - the design, build, and maintenance. Lives, quite literally, were at stake so tremendous skill and was/still is great incentive to "get it right".
I wanna take care with "new" solutions emerging since these original designs traveled 500+ million bus miles (add 3x to that with HD trucks, boats, and add untold millions of stationary operating hours in industrial usages) worldwide before any "new" ideas were even invented.
I am a "lurker" member of a couple bus forums. I researched one of them for DD "runaways".
I included a two-page thread link below that took me 30 mins to slog through because I had to keep looking up terms the posters were using.
Detroit Diesel Emergency Shutdown Dampers
The essence of the thread was this:
1. OP was commenting -- politely -- on other members' reactions to something posted about "Emergency Stop" switch on the bus dash.
2. The ES "system" on these old DD's actuates a damper system above the supercharger to shut off the air.
3. The OP had this ES system "disabled" on his DD because a GM "service bulletin(s)" said to do this. Why? Because the ES dampers' activation MAY cause the "blower seals to invert" making the engine start ingesting engine oil. That potential "drinking" its own oil event, even if runaway detonation is ultimately averted by air denial dampers, requires an engine overhaul afterward.
4. You can then imagine the "camps" staking out in other related threads (not posted above). "WhyTF would you disable the anti-runaway system", "cuz they said so", "BS, WhyTF would they do that?", etc. and so forth. This one ended with polite, mildly-debated suggestions but NO consensus and did not produce an authoritative document FROM GM.
Shot of my 4903 dash. The far left switch activates the shut-off cylinder (the leaking part) in my bus
I have better background now to discuss the issue. I did NOT, again, have a "runaway". I had/have a FEAR of one.
They are rare, it seems, in well-maintained DD's but oh my, you gotta have a way to deny a DD air in an emergency.
I gotta try to untangle this alleged "service bulletin" thing on two-stroke, blown DD'S.
GM designs an emergency, damper-based, (right where @twostick said you need it) air shutoff system, for a known but rare (but because its catastrophic in effect - basic FMEA principles) risk they encountered in design and testing, then tells people to disable it?? If true, in favor of what alternative in an runaway emergency??
Something aint hanging together yet.
This is where I get to meet the Bus Grease Monkey, ask the Whisperer when he gets back, and my guys helping me with these coaches.
Going in my "bias" is to do what the bus/diesel engine designer/builders had in mind. Yeah its old hardware, but thought went into these machines - the design, build, and maintenance. Lives, quite literally, were at stake so tremendous skill and was/still is great incentive to "get it right".
I wanna take care with "new" solutions emerging since these original designs traveled 500+ million bus miles (add 3x to that with HD trucks, boats, and add untold millions of stationary operating hours in industrial usages) worldwide before any "new" ideas were even invented.
Last edited:
Thankfully you didn’t have a runaway.
As stated above it is an emergency shutdown. They kind of give you a sucker’s choice. In the rare occasion that a runaway happens, you can either let the engine grenade or you can shut the emergency damper stopping the engine but likely needing to replace the blower seals. That being said, why’d the engine run away in the first place? Bad blower seals leaking oil into the intake?
GM was probably concerned that by putting it in easy reach on the dash, uneducated drivers would/could use it to regularly shut down the engine.
In this day and age there is at least a parallel In Construction equipment with a DPF and or SCR after treatment systems. Manufacturers found that if you put the inhibit switch within easy reach without a lockout, operators would either bump it or push it which inhibits the regeneration of the engine to clean the DPF. Inhibit it enough times, the engine goes into limp mode and you need to take it to the dealer to get the filter cleaned and the CPU reset.
So the lesson in both is to put the emergency shutdown Or Inhibit buttons/switches where you can access them, but not too easily.
Followup to #1,436. New Information Part II
Editorial. I have spent part of this morning looking for something authoritative FROM GM (Detroit Diesel) on disabling their emergency shut off systems. Until I find it/them, such document(s) are urban legends.
Frankly, while undeniably brilliant and capable people on on "forums" of all types, some could be mistaken or just plain flat wrong. Seems one in my position, or anyone "listening" to others', needs to have true experts to weigh in on stuff.
Anyway, I found a sh*tload of runaway two-stroke, blown DD "stories". Causes, prevention, what to do if it happens, etc,. but nothing yet FROM GM thAT was contemporary or superseded manuals/parts books from 1954 through 1970.
The truth is out there!
I ran across this little thread:
8v71 Shutdown Tutorial
Excerpt:
"First thing is that the engine stop lever technically doesn't "cut the fuel", which implies a valve that shuts off the flow of fuel to the engine.
What it does is put the injectors into their no-fuel position so that they are not delivering any fuel into the combustion chambers. Fuel is still being supplied to the injectors, they just aren't injecting any into the engine.
Most times if there is an "emergency stop" switch what it does is activate a electric solenoid that trips a big flap that simply blocks off all air intake into the engine.
On my MCI is was on top of the blower, and would kind of self-deploy every once in a while, thankfully not while the engine was running.
Later versions of the two strokes had different control racks which eliminated the need for the emergency shut down flap so it was no longer installed."
This fella had a 1980 MCI MC-5 with a turbo charger too. Sounds like he knows what he's talking about .. but I dunno know for sure it this is how MY GM bus works.
Reminds me of that BGM vid in #1,428 above. I think he - a professional no less. asked questions, prepped at the site, etc. - was a bit shaken when that thing went off on him. Took him only ten seconds to calm that 8V down .. but did he only have 20 seconds before he was wearing pieces of the blower or something?
Both my DD's are 1955 (4501) and 1968 (4903) designs, rebuilt at least once by me on 4501 two years ago, and I know of at least one rebuild by previous owner of 4903 in 2016.
I say this because there MAY be some factory bulletin, on some post 1968 version of 8V DD's, where injector control rack design made it UN-necessary for the UP-stream air damper system to the supercharger that MY vintage 8V uses.
OR, may not .. rather some wives tale/misinterpretation/situational misunderstanding along the way.
My point: I wanna be really sure about this runaway thing. EVERYBODY knows it COULD happen. EVERYBODY knows it COULD end ..badly.
I just wanna be preventative up front, and knowledgeable when somebody works on my stuff, and most importantly prepared in advance of an emergency.
Last thing I want is IGNORANCE (can't do anything about Acts of God, random chance) to be the primary reason somebody gets hurt cuz I wanted to be an cool, old parlor diesel "bus driver" in retirement.
I'll, no sh*t, sell/scrap (NOT repower because I want original pieces) both these sum-guns before taking this rare, runaway risk UN-seriously.
Thanks folks for your perspectives.
Editorial. I have spent part of this morning looking for something authoritative FROM GM (Detroit Diesel) on disabling their emergency shut off systems. Until I find it/them, such document(s) are urban legends.
Frankly, while undeniably brilliant and capable people on on "forums" of all types, some could be mistaken or just plain flat wrong. Seems one in my position, or anyone "listening" to others', needs to have true experts to weigh in on stuff.
Anyway, I found a sh*tload of runaway two-stroke, blown DD "stories". Causes, prevention, what to do if it happens, etc,. but nothing yet FROM GM thAT was contemporary or superseded manuals/parts books from 1954 through 1970.
The truth is out there!
I ran across this little thread:
8v71 Shutdown Tutorial
Excerpt:
"First thing is that the engine stop lever technically doesn't "cut the fuel", which implies a valve that shuts off the flow of fuel to the engine.
What it does is put the injectors into their no-fuel position so that they are not delivering any fuel into the combustion chambers. Fuel is still being supplied to the injectors, they just aren't injecting any into the engine.
Most times if there is an "emergency stop" switch what it does is activate a electric solenoid that trips a big flap that simply blocks off all air intake into the engine.
On my MCI is was on top of the blower, and would kind of self-deploy every once in a while, thankfully not while the engine was running.
Later versions of the two strokes had different control racks which eliminated the need for the emergency shut down flap so it was no longer installed."
This fella had a 1980 MCI MC-5 with a turbo charger too. Sounds like he knows what he's talking about .. but I dunno know for sure it this is how MY GM bus works.
Reminds me of that BGM vid in #1,428 above. I think he - a professional no less. asked questions, prepped at the site, etc. - was a bit shaken when that thing went off on him. Took him only ten seconds to calm that 8V down .. but did he only have 20 seconds before he was wearing pieces of the blower or something?
Both my DD's are 1955 (4501) and 1968 (4903) designs, rebuilt at least once by me on 4501 two years ago, and I know of at least one rebuild by previous owner of 4903 in 2016.
I say this because there MAY be some factory bulletin, on some post 1968 version of 8V DD's, where injector control rack design made it UN-necessary for the UP-stream air damper system to the supercharger that MY vintage 8V uses.
OR, may not .. rather some wives tale/misinterpretation/situational misunderstanding along the way.
My point: I wanna be really sure about this runaway thing. EVERYBODY knows it COULD happen. EVERYBODY knows it COULD end ..badly.
I just wanna be preventative up front, and knowledgeable when somebody works on my stuff, and most importantly prepared in advance of an emergency.
Last thing I want is IGNORANCE (can't do anything about Acts of God, random chance) to be the primary reason somebody gets hurt cuz I wanted to be an cool, old parlor diesel "bus driver" in retirement.
I'll, no sh*t, sell/scrap (NOT repower because I want original pieces) both these sum-guns before taking this rare, runaway risk UN-seriously.
Thanks folks for your perspectives.
Control racks. Stuck injectors.
Couple videos, one just a couple minutes, and the other about 12 minutes. Both vids feature 8v71's, but different vintages.
There's a "green" engine and a "blue engine. Plus the "blue" engine (8V71TA Turbo charged with After-cooling) has a "Jake Brake" system (didn't know that's on the heads!).
My buses do not have Jake Brakes. but the Whisperer tells me its something to consider for both my buses later..
Doesn't remotely make me an "expert" but even a noob like me can appreciate the "engineering" that went into these old DD's. But a bunch screws, nuts, cotter pins, etc ... seems like maintenance of/checking that stuff is key.
Yeah, they (diesel valve train/injector designs particularly) have probably advanced a lot in 70 years. But what people keep saying -- there is NO good reason why these "old" systems WILL misbehave IF well-maintained.
For me, I am learning what stuff is supposed to do, how it looks, the names of key systems, etc. I am on the road to being a better owner -- hopefully.
Anyway, the short vid is a guy going through a running engine that had NOT run in years. He's focused on the "control rack" for the injectors looking for any that are "stuck".
We know the principle runaway cause in these old DD's are "stuck" injectors .. stuck "open" could be bad.
He's trying to figure out the "what fer" on the control racks before he started the engine. Lo and behold, he had stuck injector(s) on the first side he checked.
He also said something I found interesting about control rack design changes in later vintages.
The older vintage meant ONE stuck injector had the mechanical effect on the control rack of ALL the injectors being stuck (even if there were NO OTHER injectors actually stuck on that side).
Later designs, if ONE injector was stuck, there was some "breakaway" feature that did NOT result in all being stuck.
This could be why control rack design improvements MAY .. MAY .. be why runaway mitigation with the damper-based ES systems was LESS necessary in later 8V71 vintages.
The longer video is a guy going into the "box" .. where injector control/governor mechanisms are located. I recognize the "box" on my bus .. that had my hands on it in panic mode when my bus would not shut off.
The obvious outward appearance of the blue "box" is MUCH DIFFERENT than mine, but its in approximately the same relative position on the engine .. to the upper left of the blower above the head on the outboard side of the an installed bus engine.
Tolerances in the "box" are "thousandths of an inch". Seems to me, only the most experienced people should be muckin' around in there.
I talked to the prior owner of 4903 (he sold it to the guy I bought it from, three months before I bought it). The prior owner, a carpenter/electrician by trade, is the one who up-fitted (actually remodeled an older upfit) 4903 into an RV, and had owned it for almost 2 decades.
He said something yesterday that only today makes fuller sense to me.
He told me when I have 4903 looked at for this shut-off thing, do NOT let anybody other than a professional go into the "box". The longer vid narrator/expert shows why, I think, this is true on perhaps any of these 8V two-strokes.
We'll see how she goes ...
NEWS FLASH
The fella in the long vid above gives an 8 minute tutorial (using a 6V71) with NON-spring (the kind that "breakaway" if one injector is stuck), or "safety" control racks.
The DD two-strokes' injector "default" position (goes there at shut-off, remains that way until start-up) for injectors is "open". Likelihood, therefore, if gummed up/not started for a year or longer, of runaway goes up (i.e., injector(s) stuck open) with poor maintenance/disuse.
He goes on to state affirmatively the "safety" control racks, added by GM in the 1970's he thought, eliminated the need for damper-based ES systems. He also had a few seconds on the ES damper-system and placement/operation on top of the blower.
And, now I see more clearly why on one of bus forums, the guy that wanted to DIS-able his ES damper system was gettin' sh*t from the members in #1,436.
First, he never said what kinda racks he had. And, second, nobody asked him the question about his racks when they were jumping on him.
Maybe it come up in other threads, maybe I missed it, but they were just arguing ... politely .. but totally UN-productively. Never seen that happen in a forum
.
I conclude it IS likely when the "safety" control racks were added to the DD 2 strokes, GM said "something" -- in manuals/bulletins/safety rack kits, whatever -- why they thought the damper-based ES may not be needed.
I still dunno IF GM also said you could use the "safety" racks on OLDER designs. If I had to bet, and of course now that I know what to ask, is BOTH my buses (even after contemporary rebuilds) do NOT have "safety" control racks.
And even if you could retro-fit older DD's, it doesn't seem like a smart thing for them to tell customers to disable their existing ES damper system .. unless they were VERY sure the safety control racks could PREVENT (or significantly reduce the risk of) runaways.
They ("safety" racks) were denying FUEL to the engine, but near as can tell they were NOT denying a DD air - the best way to stop a rare but potentially catastrophic runaway.
Regardless of my vintage of control racks, I still kinda like the idea of a WELL-FUNCTIONING damper-based ES, maybe with a manual pull-cable (to close the damper) that can be easily/quickly accessed in an emergency?
Now I'm done with topic for now.
Couple videos, one just a couple minutes, and the other about 12 minutes. Both vids feature 8v71's, but different vintages.
There's a "green" engine and a "blue engine. Plus the "blue" engine (8V71TA Turbo charged with After-cooling) has a "Jake Brake" system (didn't know that's on the heads!).
My buses do not have Jake Brakes. but the Whisperer tells me its something to consider for both my buses later..
Doesn't remotely make me an "expert" but even a noob like me can appreciate the "engineering" that went into these old DD's. But a bunch screws, nuts, cotter pins, etc ... seems like maintenance of/checking that stuff is key.
Yeah, they (diesel valve train/injector designs particularly) have probably advanced a lot in 70 years. But what people keep saying -- there is NO good reason why these "old" systems WILL misbehave IF well-maintained.
For me, I am learning what stuff is supposed to do, how it looks, the names of key systems, etc. I am on the road to being a better owner -- hopefully.
Anyway, the short vid is a guy going through a running engine that had NOT run in years. He's focused on the "control rack" for the injectors looking for any that are "stuck".
We know the principle runaway cause in these old DD's are "stuck" injectors .. stuck "open" could be bad.
He's trying to figure out the "what fer" on the control racks before he started the engine. Lo and behold, he had stuck injector(s) on the first side he checked.
He also said something I found interesting about control rack design changes in later vintages.
The older vintage meant ONE stuck injector had the mechanical effect on the control rack of ALL the injectors being stuck (even if there were NO OTHER injectors actually stuck on that side).
Later designs, if ONE injector was stuck, there was some "breakaway" feature that did NOT result in all being stuck.
This could be why control rack design improvements MAY .. MAY .. be why runaway mitigation with the damper-based ES systems was LESS necessary in later 8V71 vintages.
The longer video is a guy going into the "box" .. where injector control/governor mechanisms are located. I recognize the "box" on my bus .. that had my hands on it in panic mode when my bus would not shut off.
The obvious outward appearance of the blue "box" is MUCH DIFFERENT than mine, but its in approximately the same relative position on the engine .. to the upper left of the blower above the head on the outboard side of the an installed bus engine.
Tolerances in the "box" are "thousandths of an inch". Seems to me, only the most experienced people should be muckin' around in there.
I talked to the prior owner of 4903 (he sold it to the guy I bought it from, three months before I bought it). The prior owner, a carpenter/electrician by trade, is the one who up-fitted (actually remodeled an older upfit) 4903 into an RV, and had owned it for almost 2 decades.
He said something yesterday that only today makes fuller sense to me.
He told me when I have 4903 looked at for this shut-off thing, do NOT let anybody other than a professional go into the "box". The longer vid narrator/expert shows why, I think, this is true on perhaps any of these 8V two-strokes.
We'll see how she goes ...
NEWS FLASH
The fella in the long vid above gives an 8 minute tutorial (using a 6V71) with NON-spring (the kind that "breakaway" if one injector is stuck), or "safety" control racks.
The DD two-strokes' injector "default" position (goes there at shut-off, remains that way until start-up) for injectors is "open". Likelihood, therefore, if gummed up/not started for a year or longer, of runaway goes up (i.e., injector(s) stuck open) with poor maintenance/disuse.
He goes on to state affirmatively the "safety" control racks, added by GM in the 1970's he thought, eliminated the need for damper-based ES systems. He also had a few seconds on the ES damper-system and placement/operation on top of the blower.
And, now I see more clearly why on one of bus forums, the guy that wanted to DIS-able his ES damper system was gettin' sh*t from the members in #1,436.
First, he never said what kinda racks he had. And, second, nobody asked him the question about his racks when they were jumping on him.
Maybe it come up in other threads, maybe I missed it, but they were just arguing ... politely .. but totally UN-productively. Never seen that happen in a forum
.I conclude it IS likely when the "safety" control racks were added to the DD 2 strokes, GM said "something" -- in manuals/bulletins/safety rack kits, whatever -- why they thought the damper-based ES may not be needed.
I still dunno IF GM also said you could use the "safety" racks on OLDER designs. If I had to bet, and of course now that I know what to ask, is BOTH my buses (even after contemporary rebuilds) do NOT have "safety" control racks.
And even if you could retro-fit older DD's, it doesn't seem like a smart thing for them to tell customers to disable their existing ES damper system .. unless they were VERY sure the safety control racks could PREVENT (or significantly reduce the risk of) runaways.
They ("safety" racks) were denying FUEL to the engine, but near as can tell they were NOT denying a DD air - the best way to stop a rare but potentially catastrophic runaway.
Regardless of my vintage of control racks, I still kinda like the idea of a WELL-FUNCTIONING damper-based ES, maybe with a manual pull-cable (to close the damper) that can be easily/quickly accessed in an emergency?
Now I'm done with topic for now.
Last edited:
commando1
Old Man with a Hat
So much for Hernandez Diesel Repair and Burritos Station.
Similar threads
