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Tractor Pulling Discussion Forum

720 stroker

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kendak

02-23-2007 10:49:50




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I want to bore & stroke my LP 720 ...where would I find info on this project ?...what parts will interchange between models ...is there a book or manual on this ??




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Tyler Neff

02-25-2007 18:04:10




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 Re: 720 stroker in reply to kendak, 02-23-2007 10:49:50  
Since you already own the 720 I say use what ya got. Sure a G would be nice a 70 even better but if you already own the 720 I say use that . Id go with a 9.5 stroke. This would fit very well in your tractor. You could go bigger but for the amount of HP you'd gain it wouldnt be worth it. Stick with the 9.5. On the bore go with a 7in hole. It works well and you wont have to do alot of grinding to make it work. Since that tractor is so heavy I wouldnt feel to comfy going with a 7.5 bore. I think it would weaken the tractor to much and I amagine your going to be pulling the heavy classes anyway. I wouldnt do to much to weaken the mid section of the tractor like a 7.5 inch block does. Go ahead and smooth out the intake ports . Dont worry to much about the exhaust it wont gain you much. Since its an LP tractor more than likely you own the best intake manifold JD ever made smooth it up to match the head. Heres the fun one. The camshaft. I cant tell you who is the best and neither can anybody else. I have a good design that would work real nice in that tractor and I do have several out there running. Dont expect big HP from the cam and anybody promising you that is out to get your wallet. I can promise a good running tractor. Cut your rocker arms this works great and its an economical substitute for roller rockers ( which Im sure work well to if you have the extra cash)If ya wanna know more feel free to e-mail me and Ill give you my number or if you know Scott Belt out of PA call him he has the last 70 I built.

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JDGnut

02-24-2007 12:42:45




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 Re: 720 stroker in reply to kendak, 02-23-2007 10:49:50  
A few different things you can do... for a few cubes, you can use a smaller rod journal rod... JD A, 4020 or even a Case rod.. (I think a 504?? I believe is a 2.75 journal. The 20-30's have big journals so you can gain a fair amount by just offset grinding) You'll have to weld the rods.. Probably custom pistons.. They can be built to pull.. same steps as anyother 2 cylinder JD... A friend has a 730 Gas over 600cid.. its meaner than most A, G's at that size.. Good Luck,
JDGnut

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DSK

02-24-2007 09:36:38




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 Re: 720 stroker in reply to kendak, 02-23-2007 10:49:50  
It's your tractor & you can do as you want with it, but like Hauler said, the 720 should be left more or less original, as it is more of a collector tractor than a candidate for a modified puller. Several things to consider: 1. The 720 spark ignition engines are 360 cubic inches to start with, a G for example is 412 in stock form. If you were to spend the same money on each one, the G would be more powerful because it still would have more cubes than the modified 720 and the tractor pulling game is all about cubes, never mind the refined heads & duplex carbs of the later tractors. 2.Consider the parts availability and prices for a 720, they are quite expensive even if you can find what you need.3. Think about pulling the 720 in a stock class, they can hold their own against similar sized tractors. Bottom line, it's your tractor, do as you wish, there's many HP shops out there who would help you build the 720 if that's what you choose to do.

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JD hauler

02-23-2007 20:03:29




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 Re: 720 stroker in reply to kendak, 02-23-2007 10:49:50  
Many 730 parts are the same as far as tranny and motor, but being a JD fan , keep a nice 720 to restore and build an oliver, they are tough to beat and make cheaper power faster and easier than grinding the heck out of JD , my two cents.



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kendak

02-25-2007 08:18:48




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 Re: 720 stroker in reply to JD hauler, 02-23-2007 20:03:29  
thanks for all the replys but I"m not a collector & I don"t want to have to completely rebuild a [G]...friend of mine has a [G] he pulls with & is running about 165 hp....he cut out trans case so that the rods go back in transmission for more stroke....does anyone know how much the 720 block can be bored ?...I have considered putting [D] pistons in they are 6.75 ...stock 720 bore is 6in...{D] pistons also come in .250 oversize which would give me a 7in bore if block could be bored this much...the 720 is to heavy to be competitive is stock class even with rear hdy.case removed & stamped back wheels....I don"t want to use any other brand because in 30 years of farming I used only JD...plus I have never seen an Oliver,White or MM in the MS delta...it;s either JD or IHC down here...thanks again ...Kent

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Drew

02-26-2007 15:24:57




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 Re: 720 stroker in reply to kendak, 02-25-2007 08:18:48  
You are not going to be able to bore your stock block to 6.750" or 7.000". You can however, for +/- $1200 get sleeves welded into your block to go to that big of bore. That big of bore block will not just fall into place, it will require some grinding to make it fit.

If you are planning on stroking it, you will not want to use "D" pistons. My notes show a stock "D" piston compression height of 4.875". You will want a much shorter piston for a stroker application.

If you get a block sleeved, take careful measurements before you get a crankshaft made to make sure everything will work. I dont know how long a 720 block is compaired to a 70 but 9.25 is all you can fit into a 70 POWER BLOCK and not pull the wrist pin out of the bore @ BDC. Depending on how the block is done will determine if 9.500 will fit or not.

Not all cam grinders are out there to get your money. There are several reputable places out there to choose from. There is horespower to be found in a camshaft.

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tyler neff

02-26-2007 17:08:17




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 Re: 720 stroker in reply to Drew, 02-26-2007 15:24:57  
Oh well than I guess my 70 with a 9.5 stroke was all in my mind. Im sorry. This is why I hate posting stuff on here because theres always some wanna hump hump freak that knows 10 times more than anybody else. Call around Mr BIG TIME TRACTOR BUILDER and you to will find out that a 9.5 will work. Maybe you need a refresher course.



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Drew

02-26-2007 19:52:03




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 Re: 720 stroker in reply to tyler neff, 02-26-2007 17:08:17  
Maybe you need to read it again. What I was talking about was how much stroke would work and not pull the wrist pin out of the bore. If you pull the pin out of the bore then you can put more stroke in it. I tend to feel better with an engine if the pin isnt hanging out in never never land at BDC. Calm down a little!



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High Octane

02-27-2007 08:12:32




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 Re: 720 stroker in reply to Drew, 02-26-2007 19:52:03  
You two need to put your heads together and build a few good Deeres. Shoot, around here, they cant get a 9 inch G running without breaking the crank in two after 3 passes. Ive seen machinists, make sleeve extensions that some how either was welded, or was threaded onto the bottom of the block to extend the cyl down further. Wasnt much, maybe 3 inches if that,,,, Surely,, you guys have been there, and done that??? right? We took a 70 out to 6.125,,, went thru 4 blocks to find a good one that wasnt cracked,,, from the outside in. I thought the 720 was the same as the 730 blocks,,, so they may be thicker? never seen a 720-730 apart to know much, but the visual is the 730 block is shorter than a 70, if the 730 is the same as the 720, 720 block is shorter than a 70???

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JDGnut

02-28-2007 19:18:11




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 Re: 720 stroker in reply to High Octane, 02-27-2007 08:12:32  
I'm a little late on this one.. but some of the 720-730 blocks will hold 6.4.. but probably best to stay at the usual 6.375... As others have stated.. the pin location is the trick.. getting it as high as possible... The short block is the problem... You need to get the pin up in the ring area...



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