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Author Topic: 8v71 and 8v72 what is the diffrence???  (Read 12123 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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Eagle
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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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Runcutter
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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 
1968 PD-4107

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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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johnjem
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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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johnjem
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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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johnjem
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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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John E. Smith
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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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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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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 
1968 PD-4107

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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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DrivingMissLazy
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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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