leeave96

Gas vs Diesel Fuel Consumption

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Picked up a 9ft disc mower conditioner, so hp in 2018 is more of a concern now than with my old haybine.

It has been in the cards to rebuild the C291 in my 756 or replace it with a Cummins diesel in 2018.  FWIW, I’m OK keeping the gas.

However, this disc mower conditioner IMHO is capable of using every hp the 756 has to offer if I push it, even with a fresh gas engine rebuild for the C291, assuming I can make enough ground speed cutting in our lumpy, irregular fields and stay in the seat!

I think of a Cummins diesel swap into this 756 as essentially transforming it into an 856.

Soooooo

Per Nebraska tests, the 756 (via 706 data) gas loaded at standard PTO speed is 5.762 gal/hr.  The 856 diesel is 6.047 gal/hr.  Hardly any difference and I use the 856 diesel as representative of what I’d get with a Cummins swap.  The diesel 756 uses 4.675 gal/hr, again not a huge difference IMHO.

Question is - are the Nebraska tests fuel consumption data real world realistic?  I don’t know how many posts on various forums talking about what gas hogs the 706/756 were - and mine is plenty thrusty, especially compared to my thrifty 3cyl 50 PTO hp diesel tractor.

Based on the data I’m not sure I’d come out ahead swapping out the gas C291 for a Cummins 5.9 from a rebuild/vs replacement cost and fuel consumption cost and at least the C291 fits the tractor, ie bolt-up, linkages, tach, etc where the Cummins might present some additional integration challenges/costs.  I’m thinking overall, a gas rebuild pencils out better than a Cummins swap, so I’m thinking about moving ahead with the gas rebuild.

Aside from additional hp from a Cummins swap, any reason not to run a gas 756 (with fresh rebuild) on this disc mower conditioner?  Anyone running one with a gasser?

Any sage advice is appreciated.

Thanks!

Under edit:  The rational for a rebuild or Cummins swap in this gasser is multifold fold vs buying a diesel tractor straight-out.  The tractor has 4,000-ish hrs vs ragged out diesels I’ve seen north of 8k hrs and 4 times what I paid for the 756.  While the tractor needs something done to the engine, the rest of the tractor appears to be in good shape and I gather a 756 gasser’s drivetrain is probably not seen wear and abuse as their more heavily worked  much higher hour diesel counterparts, so this 756 gasser, IMHO makes for an ideal low cost foundation to build upon going forward.  To test the waters, I tried to sell it on Craigslist, but gave it a price that if someone wanted it bad enough, it would make it worth my while (and wallet) to buy a diesel, but as expected no real serious offers.  So now I’ll keep it and try to make a very nice haying tractor out of it.

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The gas will definitely burn more gallons . Gas has less btus than diesel which requires more of it to get the same energy as compared to diesel . It will have enough power to run it fine in my opinion . I'd run the gas engine till it plays out then make a swap. No sense in fixing something that's not broken. 

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Rebuilding a engine even when doing the work yourself the little things and machine work add up quick the cummins  will not burn as much fuel as the 856 I can mow roughly 12 hours pulling a 630 moco with flails with my 806 cummins swap and still have some left to spare you don’t have to rev the engine as much with the cummins it has enough power at half to two thirds throttle to get the job done

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2 minutes ago, 1989 plowboy said:

Rebuilding a engine even when doing the work yourself the little things and machine work add up quick the cummins  will not burn as much fuel as the 856 I can mow roughly 12 hours pulling a 630 moco with flails with my 806 cummins swap and still have some left to spare you don’t have to rev the engine as much with the cummins it has enough power at half to two thirds throttle to get the job done

Machine work will eat ya alive these days!!!

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58 minutes ago, leeave96 said:

Question is - are the Nebraska tests fuel consumption data real world realistic?

I've never done any precise fuel use measuring, but the Nebraska test on the 766 Diesel shows 6.1 g.p.h. max. drawbar.

When mine was stock, I remember running her dry one day (pre-T04) after pulling an 11' Deere TWA plowing disk for 12 hours. The tank held 37 gallons. Of course that included turns, and I wasn't pulling the snot out of it like I was plowing gumbo or something, but it was loaded. Not quite apples and apples, but that's quite a difference from the Nebraska results.

After we started leaning on it with a little more fuel and air, the consumption went up, but still stayed around 5 - 7 g.p.h. even then.

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Our (previous) 5140 MFD cab powershift we had for 13K+ hours I don't remember exactly but I don't think it used more than 4 gallons per hour working on the diskbine

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The 706 C291 version, the 806 gas, 756 gas, 826 gas, and 766 gas all were gas hogs. That is because they were large 291 and 301 cu in engines (as compared to the smaller C263). Forty years ago I had a C291 version of the 706 and a 656 gear drive. When working running a corn picker the 706 burnt approximately 30% more gasoline than the 656 did. So will you save money with a B series Cummins installed? Add up the costs of getting the C291 rebuilt and then add up the cost to purchase the 5.9 Cummins, the modifications and parts needed to adapt it to the 756 frame. The 5.9 Cummins should be more costly unless you got a bargain on it. Then you look at how many hours per year you will use it. In general (and this is a SWAG from my experience), if you use the tractor for less than 100 hours per year, rebuilding the gasser will be cheaper in the long run. Just my thoughts. If you could find a low hour 756 diesel and be able to trade your gasser on it, that might be your best bet. Finding a low hour 756 is at best a very long shot.  

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A cummins swap including a 1200 dollar engine is still about a thousand cheaper than rebuilding a d 360 and doing the tear down and rebuild labor yourself     If you need precise figures and costs and part numbers and pics to make it a smooth transfer send me a pm with your phone number

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3 hours ago, George 2 said:

The 706 C291 version, the 806 gas, 756 gas, 826 gas, and 766 gas all were gas hogs. That is because they were large 291 and 301 cu in engines (as compared to the smaller C263). Forty years ago I had a C291 version of the 706 and a 656 gear drive. When working running a corn picker the 706 burnt approximately 30% more gasoline than the 656 did. So will you save money with a B series Cummins installed? Add up the costs of getting the C291 rebuilt and then add up the cost to purchase the 5.9 Cummins, the modifications and parts needed to adapt it to the 756 frame. The 5.9 Cummins should be more costly unless you got a bargain on it. Then you look at how many hours per year you will use it. In general (and this is a SWAG from my experience), if you use the tractor for less than 100 hours per year, rebuilding the gasser will be cheaper in the long run. Just my thoughts. If you could find a low hour 756 diesel and be able to trade your gasser on it, that might be your best bet. Finding a low hour 756 is at best a very long shot.  

Thanks!  I’d say with hours divided up among our other tractors, we might put 100 hrs a year this 756, I doubt it would ever exceed 300 hrs.  Agree a low hr 756 diesel or any 56 series or newer IH tractor with low hrs is a long shot.  What’s worse, buying a ragged out 756 diesel with 10k hrs for $6-8k and dumping another $5-6k into a rebuild that bolted to the front of a high hour driveline.  This is what attracted me to a lower hr/lower cost gas tractor as a starting point.  Worse case, rebuild or swap the engine and you’ve got a decent tractor going forward.

3 hours ago, 1989 plowboy said:

A cummins swap including a 1200 dollar engine is still about a thousand cheaper than rebuilding a d 360 and doing the tear down and rebuild labor yourself     If you need precise figures and costs and part numbers and pics to make it a smooth transfer send me a pm with your phone number

I’m not sure where I’d find a $1,200 Cummins and then knowing what you’d have when you put it in the tractor might be a crap shoot.  I toyed with the idea of buying a Dodge with a 5.9 running and using it for a few months to vet the engine prior to a swap, but holy smoke, they are still very pricey. Another thing I’ve looked at is the mileage on these 5.9 Cummins trucks.  They are getting long in the tooth and the high mileage reflects that, so somewhat concerned there too.

My biggest concern with a gas rebuild is reliability under a heavy load when pulling a discbine.  I’ve read about these gas engines burning valves or seizing under heavy load - which would be a disaster.  Whatever I do with this 756, it needs to be a home run.  I don’t want to revisit this engine again.  Granted, won’t be like plowing for days on end, but when the hay needs cut, the work would be intense.  The rest of the year, it’s just a chore tractor and being gas, an easy starter during the winter,  I’d probably use the tractor to square bale some hay with kicker and kicker wagons in tow too, but I don’t feel that will max out the hp like running a discbine.  I’ll send you a PM - thanks!

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Don’t know about the bigger gas engines but my 706 has the 263. When I bought it everybody said I wouldn’t be able to keep gas in it. However I have been extremely happy with it. For light duty work I can get fuel consumption down to 2-3 gallons per hour. You have to really work the snot out of it to get above 5. Anyway don’t know how different the larger gassers would be, but if I were in your position with my 706,  I would rebuild the 263, hands down no question about it.

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Everyone has their own opinion, but if it were me theres no way I could justify a cummins swap. Unless your doing it for the wow factor then in that case its your money. When you can pick up a nice running diesel 756-766-966-1066 for 6-9k. I realize this is a big range but that's just how they are priced. Higher up the nicer they are. If you were just using your gas burner to rake and tedder hay or of the like gas consumption wouldn't be bad and im sure you could prolong your overhaul in light duty. Just my .02

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The 756 in question here, sounds like a perfect candidate for a diesel swap. The 5.9 Cummins is one choice, and would make the most sense. Those run nearly forever, compared to a 358 which is a good engine, but expensive to rebuild. A 360 would be a good swap, but finding a tractor one is tough, and the truck 360 is a totally different engine as far as bore and stroke, but can be put in tractors with success. The beauty of the 5.9, is that they can be found everywhere, and parts are relatively inexpensive. Will it pay for itself in fuel savings? Probably not, using only 100 hrs a year, unless your 291 takes major work to get into top notch condition. But, I'm betting it would be such a sweet tractor that you'd use it more than you originally thought. As much as I like the 5.9, I'm almost tired of seeing it swapped into anything and everything though lol! Like walking up to a street rod and seeing a small block chebby sitting in it, very generic lol! But, there is no denying, the 5.9 Cummins is a really great little engine. Now, there's one more option, rebuild the gasser, and put EFI on it, and run gas or E-85. There's a guy here in town who is making kits for JD 3020/4020's. He's pretty well known in the green world, but he's not doing any for other color tractors though. Well, I hope I helped confuse you more lol! Merry Christmas!

Edited by Injpumped
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why not just buy a 966 and have it over with. They are relative cheap for the HP and would be less money than the swap and overhaul parts are not too expensive for what you get

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2 hours ago, hagan said:

why not just buy a 966 and have it over with. They are relative cheap for the HP and would be less money than the swap and overhaul parts are not too expensive for what you get

And you can still have your 756 .   Iam sure it does if you say it does.  But why does your old gas need a rebuild?

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We've been using a gas 656 on a 9 ft New Holland 411 Discbine since about 2000. Tractor was overhauled at about 5000 hours in 2003. Fuel consumption is roughly 3.5 gah. We run in 2nd dd or 3rd dd with ta pulled as needed. (It's a 5 speed like an Mta). Have some rough ground that's hard on the body at 6 mph. Use premium fuel too. The 1256 used nearly same fuel amount and compacted ground more.

 

karl f

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The one thing I might caution you on a C291 rebuild is to select a good repair shop to rebuild it. You don't want amateurs doing it. In particular the bores of the tight fitting sleeves need to be checked after installation and finish machining of the bore ID done if necessary to maintain correct piston clearance. I learned this the hard way back 39 years ago when I had a C291 rebuilt in my 706 gas. The next owner complained the pistons only lasted 2000 hours because the skirt clearance was marginally tight when rebuilt.

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1 hour ago, George 2 said:

The one thing I might caution you on a C291 rebuild is to select a good repair shop to rebuild it. You don't want amateurs doing it. In particular the bores of the tight fitting sleeves need to be checked after installation and finish machining of the bore ID done if necessary to maintain correct piston clearance. I learned this the hard way back 39 years ago when I had a C291 rebuilt in my 706 gas. The next owner complained the pistons only lasted 2000 hours because the skirt clearance was marginally tight when rebuilt.

That’s the #1 concern I have with this C291 - the sleeves.  Sink a pile of $$$$’s into the engine, only to have it fail over these sleeves...

If it were easy, I’d have the sleeves pulled to give me C301, the heck with the sleeves, their complexity - rendering the engine a normal rebuild like any other gas engine such that a local mechanic could do it and run it until the the next rebuild at which time I’d consider another rebuild, engine swap or retirement... 🤔

But I don’t think making a C301 out of a C291 is an easy button....

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Did any of the old combines have the right engine in them? Dad had a couple old 303 combines that were 6cly gas? 

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Down here in the south you can find old 782 cotton pickers with a D-310 for $750 to $1000. That would be the way to go.  Eason

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If it was me I would overhaul that good old 291 there are getting to be less and less big old gas tractors out there! 

I am kinda looking for something like your 756 or 806 gas too use around the farm right now cuz it's like 20 below out and gas gives less troubles in cold the diesel  does! 

I have some smaller gas tractors but nothing with both pto's and my manure spreader and my TMR mixer both are BIG and take 1000 rpm pto!

so like the one guy said just get a 966!

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So we are talking about a 4,000 hour 756 right? I wouldn't worry about longevity if its rebuilt right.  We ran a discbine with a 656 and it handled it just fine. Our 460 ran it from time to time as well. A 4,000 hour engine shouldn't take much to freshen up. I personally wouldn't mess with a diesel swap if the discbine is of acceptable size for the HP rating of a 756.

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