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Author Topic: Ok, so talk to me about these engines, the DDs in particular...  (Read 3227 times)
Geom
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« on: June 23, 2013, 12:09:29 AM »


The 6v71, 8v71, 6v92 to be very specific (along with other connected essential systems -tranny, cooling, brakes/air, steering, etc).

Are they really as "fragile" as some of the posts would seem to indicate?

It seems that there is a very ritualistic approach to keeping these babies running and these rituals seem pretty important. There is also a lot of paying attention to some very important things, regularly. It also seems like there will be a sizable maintenance component involved. And even with that it seems the risk of catastrophic failure, either due to $*** happens or user error, is seemingly high.

I apologize if this has been asked before, but one of the things that drew me to a bus was the reliability aspect. So I'm conflicted.

I completely understand the need for regular and proper maintenance.
So in these buses is that a few hundred dollars a year, a couple thousand a year, or many thousands a year? Average about 5-10k miles per year.

I completely understand (and relish) the need to be attentive. And I'm more than willing to listen to everything and all that, etc.
But how much of that is "art" and how much is science?
Is it just a gut feel something doesn't sound right and a process of elimination as a result of constant "looking things over" or is it paying close attention to a few key things and look for occasional out of place things?

How much of an oh-$#** bucket should one plan for and based on what criteria?
Am I expecting "the big one" any time, all the time, just over the next hill; or -oh look that thing broke, every once in a while?

Overall. Realistically as possible. From your own experience or direct observation.

Thanks
Geom
 

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« Reply #1 on: June 23, 2013, 02:06:09 AM »

I see the issue as some folks have a feel/understanding about mechanical things, and seems most do not.
The aware folks, who keep an eye on the overall for signs & sounds.
Then there are the folks who only know something is amiss when it stops running.
Me, I am a nut case, when I purchased my MC7, it was with the understanding it needed everything, so by the time I am thru with it, it is a 100% rebuild bumper to bumper, spent much $$$$$$ on it, loved every minute of it, and it never gave me anyting but joy, always brought me home smiling, yes I put over 200K miles on it, every state east of the Miss including Canada from Detroit east.
SO I guess it is what it is.
I learned the DD engines, was lucky having played the 12V-71 game too for 4 years.
Dave M
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« Reply #2 on: June 23, 2013, 05:24:37 AM »

My take on all of this is that because of a recent high-profile engine failure, there are a lot of engine horror stories circulating. In reality, the DD 2-stroke is at least as reliable as any other mechanical device, and a LOT more reliable than some given proper, regular, reasonable attention. I think there are two key points to be made:

a. Unless you got a zero-time rebuilt engine, there's no way to know the exact history of it. I'm OK with that the same way I'm OK with buying a used car. I did my research and found what I was comfortable living with. As time goes on and I log more miles, I'll become even more comfortable with it the way I hardly think about the fact that my daily driver is a used car now. Yes, when something catastrophic happens, it has the capability to be expensive to fix, but that comes with the territory, and that's why I put money in my "oh poo" fund. Without proper preventive maintenance and attention to detail, any mechanical thing is always one step away from, uh, soiling itself. Keeping up with it is no more difficult than getting the proper manuals and educating yourself about its workings. People tend to fear what they don't understand, and with a better understanding comes an increased confidence.

b. The key to mitigating disaster is detecting problems early. It doesn't take long for small problems to become big ones. The good news is that if you catch it early, you have a good chance of preventing a meltdown. Early detection means checking things early and often in the driveway, and on the road. Every time I stop I walk around my bus with an I/R thermometer and shoot the tires, hubs, radiators, cylinder heads, etc. I'm looking for any problem that could become a big one later. This may seem excessive to some, but I don't prefer sitting on the side of the road broken down. I also think it's important to have proper warning devices on my bus. Low water, high temp, oil pressure, etc. All of these are early indicators of problems and a LOT cheaper to install than a new engine. Airplanes have tons of engine monitoring sensors because pilots need to know the status of things early if there's a problem. Our bus engines are so far back there and out-of-sight that it's harder for us to catch things until it's too late.

Sorry if this was too basic or didn't answer your question. It's just been my experience that I build a certain trust and relationship with mechanical things that I depend on by educating myself and keeping a watchful eye. Of course there's always the random, unforeseeable, wacky thing that happens, but even then I can at least feel a little better knowing I did absolutely everything humanly possible to avoid it.
« Last Edit: June 23, 2013, 05:34:53 AM by Debo » Logged

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« Reply #3 on: June 23, 2013, 05:42:55 AM »

Geom:

Whenever I buy a used vehicle (including our buses), I begin going over it with a fine-toothed comb. In our coach, we changed out all airlines, water hoses, brakes, wheel bearings, clutch and put in a new radiator. We also rebuilt the air compressor (It was full of oil.) and generator. The engine received new pistons, sleeves and oil pump. The heads were also rebuilt. I have the huge advantage of living in Mexico, where labor is much cheaper than North of the border. My engine cost me the equivalent of about U. S. $4,000. My brand new core for the radiator, with installation, less than $600.

My thinking is (from my online research) that with proper maintenance this should last me 500,000 to 600,000 miles, so in that context, not that expensive.

You might also take into consideration that a huge number of the buses on this board are 30, 40, 50 years old and a couple even older than that. Many a bus purchased by a typical bus nut has over 1,000,000 miles on it or far more... and still running great!

Many a commercial semi runs 100,000 a year for years, using some of the same engines in our buses.
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« Reply #4 on: June 23, 2013, 06:12:02 AM »

Absolutely critical to keep them cool.
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« Reply #5 on: June 23, 2013, 06:20:35 AM »

The only negative I see is the age, condition of the bus you choose . I hate to say it but right now if you can find a bus that has been redone by a bus nut ( new tires , rebuilt eng. all air stuff , brakes  gone over and all the regular things we bus nuts have done . Or for the size you want I would go with a 1990 to a 1995 bus 40' long with a newer 4 stroke and a auto trans. Now you would still have to have the eng. rebuilt at some time in the future as usually the reason they are for sale is they will need work to stay in the commercial world .The older busses are great but will usually need a lot of work and money to make them reliable .  

Now said all this my bus has had all the updates by me for maybe $ 25,000 and is still a money pit but out of choice now .Yearly maint. is only $1000. or so . change , oil , filters 2 on trans. 1 on eng. 2 fuel filters 1 air filter , grease , adj. small stuff.     Would I sell it yes but I would buy another and do it again    bus nut  thing                  


 dave      
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« Reply #6 on: June 23, 2013, 06:34:32 AM »

They just aren't reliable at all Angry  (sarchasm) The V71 series was introduced in the 1930's and is still under contract with the army until 2025 in self propelled guns. No electronics, it it's got air and fuel... it runs.  High heat is it's achilles. Anything mechanical is subject to failure.  Pound for pound they're probably the same or less to repair than any other modern Detroit, Cummins or other.
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« Reply #7 on: June 23, 2013, 06:35:46 AM »

Don't ever buy a bus thinking they run the same mileage as truck engine not going to happen buses are tough on engines the 60 series may last 700,000 miles in one top expect about 1/2 the life of any engine in a bus Cat,Cummins or Detroit 

Of the 3 you mention the 6v71 would be my least desire to own good little engines in their right application and a highway coach is not it as Harold said keep a diesel engine cool or pay the price
« Last Edit: June 23, 2013, 07:12:01 AM by luvrbus » Logged

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« Reply #8 on: June 23, 2013, 12:44:01 PM »

I am running 8V92, and it runs perfect, but when the temp outside gets over 100F, she gets over 200 in the engine.

Never a whisper of trouble, though I do get concerned at that high temp.

Thinking of changing to a larger rad. Good idea? (question to those in the know)
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« Reply #9 on: June 23, 2013, 07:01:19 PM »

I have the 6V-71 but also a Saudi bus with larger cooling system and 2 larger Radiators. It runs about 160 -170-180 if it is really hot out.

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« Reply #10 on: June 23, 2013, 07:34:22 PM »

wow!  If I was a new prospective bus owner I would be scared to death of the big bad detroit engines.  When I was looking for a bus this site ran the praises of these wonderful engines.  My first coach was a GM4106 with 8v71.  I knew nothing about it other than what friends on this site and other bus nuts taught me.  I am not a mechanic  and didn't do all the rebuild stuff.  I drove that bus with no major problems.  From Alaska to Arizona many times and across the US coast to coast.  I now have a newer bus, 1975.  When I first got it it had some engine problems from previous owners hotrodding it and a bad rebuild.  Since it was rebuilt no major problems.  Been to Alaska and back many times.  i am not afraid of running it anywhere. If it will start it will run.  One of the most dependable motors IMHA.  15 years and mostly a fulltimer.  Sit back relax and enjoy that beautiful sound of a Detroit purring.
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« Reply #11 on: June 23, 2013, 07:50:41 PM »

Sorry, Didn't answer question.   4106 no $$$ other than oil changes, filters $300.   Mci once I got the rebuild done proper. No engine problems.  Broken Altenater bolt.  Regular maintenance.  $300.
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« Reply #12 on: June 23, 2013, 08:11:55 PM »

The 2-stroke Detroit Diesels were first designed in the late 1930s.  In a Grey Hound type Bus Conversion, the engine is usually in the rear with the radiators(s) on the rear sides.  Some older Crown Supercoach school buses had the engine in the middle under the floor, but the radiator was still on the side.  Even when things were perfect, the cooling system layout left something to be desired.  Heavy trucks have the radiator right in the front where it receives the full air blast.  Bus overheating concerns were never completely overcome.

Buses are heavy kinda squarish vehicles designed to make money hauling people around.  While constructed well enough to work fine as designed, they were most not over designed simply for that notion alone.  They were just good enough to do the job and not much historically was ever added to let them do the job any bit better.  Having said that, some buses did show excellent engineering forethought and construction techniques.  They are complicated machines mostly from an earlier era of history.

They are also maintenance intensive; examples would also include airplanes; pleasure power boats, sail boats, heavy machinery, race horses, fast beautiful women and big alligators.  They require time and $money$ just sitting still in your driveway or large shop garage.  The reason why I sold my old Crown Supercoach, (vin 37317) was because I could no longer afford to MAINTAIN ONLY the planned Bus Conversion project.  Small, much cheaper, stick and staples RVs also are expensive to own, but not as much.

hope this helps some.  HB of CJ (old coot)

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« Reply #13 on: June 23, 2013, 08:51:07 PM »

When Greyhound ordered their buses with 2 stroke engines, they were detuned way down with using 55 or 60 injectors. That's because most bus drivers use the gas pedal full floored or no pedal-very little in between. When any of the 71 engines are detuned to 55 injectors (6-71 would have 195hp and 510lb/ft torque; 8V-71 would have 257hp and 677lb/ft torque) they would just about run forever-and it could just about take forever to get up the hill. As contrast, my 8V-71 turbo puts out 375hp and 1125lb/ft torque. The last 8V-71TA that Detroit made put out 400hp and 1200lb/ft torque with 7G80 injectors. But-I also do not run with my foot to the floor. I'm very gentle on the gas pedal (mainly to try and get better fuel mileage) and to keep heat down.

As said-heat is the killer for 2 stroke engines-mainly because they never relax. Each stroke is a power stroke-compared to a 4 stroke engine that has the extra 2 strokes to cool down in between. Good engines, but they do need attention. The new 4 stroke engines with common rail fuel injection, exhaust gas recirculation, catalytic converter, Diesel particulate filter, Selective Catalyst Reduction (Urea or Diesel Exhaust Fluid) are far superior to anything ever made. We have 80,000lb rigs pushing the 9mpg range. That's efficiency! Good luck, TomC
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« Reply #14 on: June 23, 2013, 10:17:57 PM »


Thanks for the responses, great info!

Ok, so if I gather from bits and pieces from the responses, the general consensus seems that,

Yes they can be a bit of maintenance, but mostly a labor of love and manageable.

Paying attention is important, as small things can become big things quickly.
(I love that I/R thermo idea Debo)

The occasional walking around poking at things ritual is important.

Heat, and reduction thereof, is key. (Which makes sense with a rear mounted engine with minimal air flow).

Regular, turn key -> vroom, maintenance is about $300 to $1000 (I've heard as high as $2500) yearly.

Short of the exciting story that everybody hears about that thing that happened somewhere to some people, they're otherwise reliable machines.
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« 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. Smiley
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« 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 » Logged

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« 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 Smiley ).

 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. Smiley

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 Smiley

Thanks all again for all the advice!
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« 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 » Logged

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« 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?
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« 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.
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« 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.
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« 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 » Logged

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« 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...



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« 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
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« 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
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« 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. Shocked

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« 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.

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« 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 Smiley

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?
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« Reply #29 on: June 24, 2013, 06:20:08 PM »

I would worry about something else besides a runaway engine Huh with a 50 year bus that should be the least of worries
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« Reply #30 on: June 24, 2013, 06:25:03 PM »

I would worry about something else besides a runaway engine Huh with a 50 year bus that should be the least of worries

Cheesy cool, one less thing to worry about...
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« Reply #31 on: June 24, 2013, 06:35:28 PM »

 One thing is certain,, no engine will run without air, so it is an option.>>>Dan
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« Reply #32 on: June 24, 2013, 07:35:07 PM »

Ok the DD blower is a roots blower it has lobes most bus people all they see are the 2 lobe type which is standard those lobes are not solid they are hollow made with thin aluminum with plugs in each end  

When the engine spins so fast on a 8v71 it happens around 3800 to 4000  rpm it blows the plugs the lobes will swell and shuts the engine down I have saw this happen before on a bad buffer switch adjustment and no I didn't do the adjustment  

90% of the time when one over revs above the limit it will cost you a blower not a engine they don't throw rod,pistons and debris all over the place as some visualize they may spin a bearing and most the time that doesn't even happen  

Sometimes I wonder how GM and Detroit made the 8v71 without the help from the internet and a bus board  Roll Eyes worry about other things geez
« Last Edit: June 25, 2013, 02:57:03 PM by luvrbus » Logged

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« Reply #33 on: June 24, 2013, 08:17:48 PM »



Sometimes I wonder how GM and Detroit made the 8v71 without the help from the internet and a bus board  Roll Eyes worry about other things geez
That cost me a mouthful of Pepsi!
Mark



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Mark & Char
1976 P8M4905a 8v71 v730
British Columbia Canada
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« Reply #34 on: June 24, 2013, 11:44:04 PM »

Luvrbus - thinking 'bout changin my addy to LuvmyLuvrbus - your hilarious - in a good way - thanks for the LOL
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« Reply #35 on: June 25, 2013, 06:08:41 AM »

Luvrbus - thinking 'bout changin my addy to LuvmyLuvrbus - your hilarious - in a good way - thanks for the LOL
That cost me a mouthful of Pepsi!
Mark



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You guys ought to spend some time with him in person!
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A curmudgeon's reputation for malevolence is undeserved. They're neither warped nor evil at heart. They don't hate mankind, just mankind's absurdities. They're just as sensitive and soft-hearted as the next guy, but they hide their vulnerability beneath a crust of misanthropy.
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