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Author Topic: 8v71 and 8v72 what is the diffrence???  (Read 12117 times)
johnjem
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« on: April 07, 2007, 07:53:55 AM »

i have a 1970 gmc 4905  with a 8v71 and i was looking to replace my motor that has blown rings i have a another bus i can buy a 1950"s gm  with a 8v72 so he clams i may be buying the whole bus from him all i need is the motor will most likely part out the rest of the bus it is all complete but the interior has been removed but all still there any  so what is the diff?between the motors?? john
« Last Edit: April 07, 2007, 07:57:14 AM by johnjem » Logged

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« Reply #1 on: April 07, 2007, 08:02:37 AM »

Do a Google search for each one of them for the information.
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« Reply #2 on: April 07, 2007, 08:44:08 AM »

John, something doesn't ring quite right - I strongly suspect the "72" is a typo - it could be a 71, or a 92.  The larger engines I'm familiar with are the 8V71, and the 6V92, 8V92.  The first number refers the number of cylinders, the second to the cubic inches per cylinder.  The V is a V configuration (two banks of 4).  If you see 6-71, that's an in-line engine; 6V-71 is the V configuration of essentially the same engine.  That's the quick and dirty explanation of Detroit models you'll find in later buses. 

That leads to the second question - if I remember correctly, the first 8V71's were in PD-4106's (1964 or so).  Older (1950's) buses had smaller engines, unless they were re-engined (including Scenicruisers).  So, the year of the bus you're mentioning, and the engine model don't tie together, unless it's been re-engined.

None of this even addresses the issue of fixing your engine (have you talked with the fellow I mentioned?) versus replacing it.  Think of the question - do you fix the car you have, or buy another new car - same thing. 

Remember, the previous owner of your coach is, in my opinion, absolutely trustworthy.  I've relied on his advice - and would do so again.  To be fair, if you want some of his time and advice, there's nothing wrong with buying some of his consulting time, or dropping by with a restaurant gift certificate and a question.

For anyone who thinks I'm being a little vague, I don't want to run afoul of the rules or the spirit of this board - John bought his coach from a dealer, and this board is owned by another dealer - so I think it'd be inappropriate to be more specific on who is who - plus, we're trying to help John with a specific quesiton.

Arthur 
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Arthur Gaudet    Carrollton (Dallas area) Texas 
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« Reply #3 on: April 07, 2007, 08:44:33 AM »

There must be a typo somewhere.  There is an 8V71 that is typically not turboed and an 8V92 that is typically turboed.  The last two numbers are the displacement, in cubic inches, per cylinder.  Detroit Diesel made a lot of different two stroke engines, but not an 8V72 that I know of.

The 8V71 is sometimes called a "318" since that was a typical horsepower configuration.  The 8V92 is often in the 450 to 500 HP range.  

To switch to a 8V92 from an 8V71 will generally require quite a bit of work.  Not even sure you can get it into a GMC.  If you can, the next big issue is cooling the engine.

Edit:  Oops, drafted at the same time as the previous post
« Last Edit: April 07, 2007, 08:46:32 AM by rv_safetyman » Logged

Jim Shepherd
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ChuckMC8
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« Reply #4 on: April 07, 2007, 08:51:14 AM »

Arthur, If John bought the bus from this guy, why would he need to pay him to ask him a question?
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« Reply #5 on: April 07, 2007, 09:13:26 AM »

 Hey guys<thanks for all the info! yes i do trust the person i bought the bus from <he gave a me a# of a good friend of his to work on my bus and he gave me a price on the engine work! the price was a bit high more then what i paid for the bus,so now i do more home work and to see what is the best for me 2 do next,i found a bus for sale for a fair price  running no smoking he said it was a 8v72 but was not sure.

So i ask the more exprienced people (this board) for some advice! If i buy this bus for half the $$ i would be spending to have a my 8v71 redone<i will be saving 4.000$ and i will have a good running motor (if it will fit as i asked in the subject line above-i will have a complete bus with generater and the hole 9 yards 2 scrap-junk-sell-sell-use parts for me and at the end i would have made all my money back+ some<is that the name of the game or do u all have a money tree out back of ur house  laugh laugh!! my mind never stops it goes and goes. 
so here it is 
i paid $$ for the bus
blown engine =over 12.000$ to get rebuilt i have many qoutes
bus i may buy 8.000$ with a good motor 8v72??  and full of every thing just not put together .
i may be saving 4.000$ and the rest  i shall sell
and spare money to plant money tree seeds in my back yard
just playing the feild see what is out there and looking for the best deal   u guys are great    john
and yes i sure would buy another car to fix up the first car i love spare parts< love going to the junk yard  when i need that part i will have it some where i will have it,u guys are awsome
so i ask do u think it is a 8v71 or 8v72  he may not have given me the right info ?
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« Reply #6 on: April 07, 2007, 09:36:25 AM »

pss i bought my bus from the owner of a dealer on a private sale Smiley Smiley
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« Reply #7 on: April 07, 2007, 09:39:46 AM »

so rv saftey man u think its a 8v71 not a 8v72 i think so 2 i will e-mail him back and see if i can come down and get the ## of the block itself thats rv.
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« Reply #8 on: April 07, 2007, 09:46:59 AM »

Detroit Diesel does not have an engine designated as an "8V72".  It is either an 8V71 or an 8V92, and judging from the year, I would imagine that it is an 8V71.

On the issue of swapping a '92 in where a '71 used to be, it will fit.  The major issues are engine cooling -- the '92 will need more cooling capacity -- and available height in the engine box.  The '92 is about 10" taller than the '71 because of the turbo.  However, there are aftermarket intake boxes available that remove or reduce that height difference.  We make a intake box for Eagles that allows you to put a '92 in any eagle by relocating the turbo behind the engine with an intake tube going up to the modified intake box.

Basically, swapping out a '71 for a '92 is not that big of a deal in most busses.
« Last Edit: April 07, 2007, 10:01:46 AM by John E. Smith » Logged

John E. Smith
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« Reply #9 on: April 07, 2007, 09:53:07 AM »

Make sure the motor is in a bus that the motor is in a sideways configuration or the rotation will be wrong.
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TomC
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« Reply #10 on: April 07, 2007, 10:20:25 AM »

Sounds like a good deal to buy the other bus with the 8V-71.  I personally would not just swap the engine without opening it up for an inspection.  You can have cracked or broken rings, cracked head, burnt valves, marginal bearings with the engine still running what sounds just fine.  I would at least do a ring and bearing job, check the heads for cracks and grind the valves.  It will involve a few more thousand, but then you know exactly what you got.
For example- I had my engine overhauled 6 years ago.  Last year I had Don Fairchild turbo the engine.  He basically took the engine almost all the way down.  He pulled one piston a found it had the proper rings, so that stopped there.  But he found the key way powering the oil pump was about to go; and when the first mechanic changed my belt driven fan to gear drive, he did open up an oil passage for it, but did not put a restrictor in it, so I didn't have very good oil pressure on the rest of the engine.  Don installed a drilled bolt, and magically oil pressure.  Also, while the engine cradle was out, I decided to have the V730 transmission checked out, even though it worked fine.  They found the forward and 3rd gear clutch about gone.
My point-Diesels can feel and run just fine, but when they go it far more expensive to get them fixed then to do preventative maintenance on them before it happens-many times by either running hours or mileage.  Good Luck, TomC
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« Reply #11 on: April 07, 2007, 10:24:41 AM »

Chuck, my thought is that the deal is over and done, with someone who's in business to make a living.  I purchased my 4107 from the same person, who went over and above the call of duty.  I showed my appreciation in a tangible way at the time.  

The way I take care of my clients is.... minor stuff, quick question, help, etc. ... I consider that I'm doing a favor for a client/friend.  If things start to add up with my time and it starts to run into work, (particularly if it takes me away from other obligations) the meter starts running.  I've had folks ask me to bill them for the time and I've refused, because it was no big deal.  I've also had a transit property call me several times, all relatively minor stuff, and I finally had to tell them that they were starting to run into billable hours.  My product is my time and expertise, they probably didn't realize that their minor questions were starting to detract from my other obligations.

Personally, I have a number of questions for this dealer, because I value his advice/opinion.  On the other hand, I wouldn't feel right bugging him with my stuff (our deal was concluded last August) without showing my appreciation for his additional effort.  For me, I'm less interested in someone possibly feeling "taken advantage of", it's more important for me to never feel I'm taking advantage of another's goodness.  That said, if I run into him at the bus museum in Hershey (remember, it's June 2), or some other place, I'll ask my questions --- AND buy his lunch.  

Just my suggestion.

Arthur
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Arthur Gaudet    Carrollton (Dallas area) Texas 
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« Reply #12 on: April 07, 2007, 02:32:42 PM »

The 8V72 DD Engine is a Marine engine model #5082-5000 that develops 283HP at 2800 RPM.  This was used by the US Navy.
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bus05eagle
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« Reply #13 on: April 07, 2007, 04:11:41 PM »

I think you will find that the 5082-5000 are 53 series
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« Reply #14 on: April 07, 2007, 04:35:46 PM »

The 8V72 DD Engine is a Marine engine model #5082-5000 that develops 283HP at 2800 RPM.  This was used by the US Navy.

Sure doesn't seem like very  much HP for that big an engine spinning that fast.
Richard
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« Reply #15 on: April 07, 2007, 06:01:59 PM »

I'm still skeptical.  I tried a few google searches.

For the keywords 8V71 "Detroit Diesel" (a known valid engine) there were 748 results.
For the keywords 8V92 "Detroit Diesel" (another known valid engine) there were 9280 results.
For the keywords 8V72 "Detroit Diesel" (the one in question) there were only 3 results.

There are no references to any 72 series engines on the Detroit Diesel site (google:  8V-72 "Detroit Diesel" site:detroitdiesel.com yields no results)

Diesel parts sites do not list any series 72 engines.

There aren't any 72 series engines in this rather comprehensive list of Detroit Diesel engines.

It wouldn't make sense for one manufacturer to produce and maintain two different engine lines with only a one cubic inch per cylinder difference.

So, while I could be profoundly wrong, I don't believe Detroit Diesel made a series 72.

« Last Edit: April 08, 2007, 02:46:08 AM by HighTechRedneck » Logged
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« Reply #16 on: April 07, 2007, 06:06:46 PM »

Quote
For the keywords 8V71 "Detroit Diesel" (the one in question) there were only 3 results.

Did you mean 8V72?

Richard
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« Reply #17 on: April 07, 2007, 09:03:34 PM »

Yep I call BullSh!t on the 8v72.........would even put a wager on it not existing.  There is no way DD would build an engine with 8ci more........it just doesn't make sense on so many levels.

The Navy used 8v71's and 6-71's which are both common marine engines
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bus05eagle
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« Reply #18 on: April 07, 2007, 09:50:37 PM »

the navy used alot of 6v53s the one eagle is talking about 283 hp at 2800rpm sure sounds like a 6v53 i never seen a 8v53 but i know they could get 400hp from the 6v53s and is a common marine engine
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« Reply #19 on: April 08, 2007, 03:01:31 AM »

Quote
For the keywords 8V71 "Detroit Diesel" (the one in question) there were only 3 results.

Did you mean 8V72?

Richard

Thanks for pointing that out.  You are right, that line should be pointing out that for the apparently mythical 8V72 there were only three google results, compared to the more typical hundreds or thousands of results for the known valid engines.  I have edited the post to correct it.
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« Reply #20 on: April 08, 2007, 06:23:28 AM »

Detroit 2 stroke series made- 51 (made for a short time-no valves-just ports, didn't work well, were made in 2 and 4 cylinder), 53 series (2, 3, 4, 6, 8, 12 [2-6V's put together] cylinder), 71 series (1, 2, 3, 4, 6, 8, 12, 16 [2-8V's put together], 24 [2-12V's put together] cylinder), 92 series (6, 8, 12 [2-6V's put together], 16 [2-8V's put together] cylinder), 149 series (8, 12 [2-6V's put together although a 6V was not made], 16 [2-8V's put together}, 20 [2-6V's on the ends with a 8V in the middle-very strange-but worked!] cylinder.  The 283hp @ 2800rpm is a non turbo 8V-53, was used on boats alot-especially Hatteras.  Hard to find parts and had a weak gear train (weaker than the other 53 series that all had weak gear trains).  Would stay away from all 53 series-are loud and for our purposes, do not produce enough torque.  Even though the 6V-53 could put out 400hp, it only had about 650lb/ft of torque.  With that output, a 6-71 would be a whole lot more dependable, and could crank a 6-71 up to 2800rpm where it would put out 300hp.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #21 on: April 08, 2007, 06:47:39 AM »

hi guys thanks for all the good info we all learned alot on this 1  i just got a email for the guy with the bus it sounds like a good deal like i said all i what is the motor here is the email u guys tell me if it sounds like a deal
-------------- Original message --------------

Hi John without digging out all the paper work and from memory the motor is an 8v71 it was out of frame rebuild about 110 to 120k ago it runs strong and when worm doesn't smoke it doesn't drip oil on a 2400 mi. trip it used 4 qt. of oil. the trans. is auto allsen v730 3 speed that was installed by a dealer in 97. there is a new radiator I installed in 2003 I have the repair manuals for the bus. it has a power teck diesel 6.6k generator a norcold refrigerator model N841.3 3 way 7.5 cu. ft. I just got a recall on the refer and once it gets a 1 year warranty there is a new magic chief stove 3 burner w/oven splendide 2000 washer/dyer 6 gal. hot water heater 2 13.5k roof ac. 90 gal. fresh water tank 90 gal gray/black tank charge wizard power converter this has a prosser in it so you don't over charge your house batteries there is a full size sleep# bed remco power w/heat mirrors peninsula windows all round I still have one in the box and many other parts that I can't think of right now. $8000 firm Russ
 That was the email   tell me if it sounds good john
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« Reply #22 on: April 08, 2007, 06:50:30 AM »

also keep in mind i will be parting out the bus it is a 1950s gm 4906   ?on the 6
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« Reply #23 on: April 08, 2007, 07:09:39 AM »

4903 or 4905.......neither of which are 50's buses but rather 60's/70's/80's
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bus05eagle
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« Reply #24 on: April 08, 2007, 07:58:19 AM »

Tom they also made a inline 6 110 it was used in the AC HD20 dozer and for heavy duty trucks
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« Reply #25 on: April 08, 2007, 09:24:44 AM »

You're right about the 6-110, but forgot about it since it was only an off road engine.  Interestingly, the first series had a gear driven turbo supercharger, then later had the familiar roots blower.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #26 on: April 08, 2007, 10:46:14 AM »

JohnJem -

Ask this fellow for the VIN on the bus you're considering, that will tell us a whole lot more.

 Wink
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RJ Long
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« Reply #27 on: April 08, 2007, 12:32:20 PM »

John. Why would you go to all this trouble if your engine just needs a set of rings in one hole? Is this the engine that had a recent rebuild and had a piece of ring in the pan? Why don't you treat this like its a fleet engine? Is it using enough oil to come out of service? Is it missing? Does it have bad blow by? There are places in the 71 where a broken piece of ring can hide from a rebuilder for a long time and fall in the pan when it gets good and ready. I have been told you can rering a 71 from the oil pan if you turn the crankshaft just right, (slide the rod and piston out the bottom). You can do this your self, pull the cylinder inspection covers and determine for sure you have a broken ring and what cylinder, pull the pan, unbolt the rod and bad piston and slide it out. Inspect the piston, if the ring lands are still in spec, rering and reinstall. Pan gasket and rings around $100. I've been told Trailways and Greyhound would put used pistons from one engine into another and put a bus back on the road. If you have a broken compression ring, it does have more than one compression ring. If you have a broken oil ring, it could still be doing a fair job of oil control, depending on how its broken. I hope this unit wasn't out of serviced because a piece of ring was found in the drain oil, because that doesn't prove much. If you pull the pan and roll the engine thru, you can check all the liners for scoring, if you don't find a real bad one, I think you will be happiest with a cheap fix.
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