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Tractor Pulling Discussion Forum

1955 JD 70

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Ben Nichols

11-30-2004 09:42:35

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Re-building a JD 70 gas to use for pulling and want some suggestions on how much you can (should) mill the cylinder head to up the compression. I am having it bored .90 over with high compression pistons and a competition grind done on the camshaft.

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12-01-2004 14:12:09

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Re: 1955 JD 70 in reply to Ben Nichols, 11-30-2004 09:42:35

I am yousing 60 rods 3inch journels off set stroke you willpick up3/4 stroke yous stock pistons move oil ring up replace bottom comp ring good head job use stock valves go to big you loose vilosity just dynoed mine last night 78 HP still have to do alittle tuning i think i might sqeeze 80

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G/MAN

12-02-2004 15:38:01

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Re: 1955 JD 70 in reply to jl, 12-01-2004 14:12:09

How do you gain 3/4 of an inch of stroke by offset grinding 3/8 of an inch off the journal? All of the material can't come off one side of the journal, or am I missing something?

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JDGnut

12-03-2004 16:54:22

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Re: 1955 JD 70 in reply to G/MAN, 12-02-2004 15:38:01

GMAN... its fuzzy math.. grind .300+ off the back side of the rod journal.. which moves the center of the rod .150.... (.150 up.. .150 down... ) not sure.. but mine never seemed to add up to 3/4.... But that is a good set up... 7.3 stroke with the LP pistons.... I tried to buy the set on Ebay a few days ago.. but they started to get pricey... for used pistons..
JDGnut

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12-02-2004 18:20:38

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Re: 1955 JD 70 in reply to G/MAN, 12-02-2004 15:38:01

Your pushing piston 3/8 up and3/8 back stock stroke is 7 in with 3 3/8 journel know your going to 3 in journel cuttingjust bottom side of journel when you off set grind crank need to weld very little for cheeks because 60 rods 1/4 thiner you will end up 73/4 stroke

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JDGnut

12-03-2004 21:14:18

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Re: 1955 JD 70 in reply to jl, 12-02-2004 18:20:38

JL.. I'm not trying to argue with you... but we've been there and done that...
When you offset grind... you are moving the center line of the journal... If 3.300 is your starting journal size... The center of your rod journal is 1.65 (half the diameter.) Offset grind.. taking off .300 off one side of the journal.. moves the center of the journal only moves the center line of the journal to 1.5... This drops the piston .125 lower in the cylinder.. and pushes it .125 further up in the cylinder.. adding only .300 to the total stroke... This is difficult to explain... but if you had any welding done on the crank... then you could have a 7.75 stroked crank... At that distance you are starting to get close to the cam with the A rods... JDGnut

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12-04-2004 14:01:39

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Re: 1955 JD 70 in reply to JDGnut, 12-03-2004 21:14:18

JDGNUT yes you are correct i just was not explaining my self correctly we did weld cheeks and little on top sorry for confusion make some good power with off the shelf parts with out breaking bank and very realiable too

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G/MAN

12-03-2004 07:30:28

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Re: 1955 JD 70 in reply to jl, 12-02-2004 18:20:38

I've never heard of gaining that much stroke with the offset grind. The few people I've talked to that have done it mentioned gaining less than half an inch of stroke. Have you done this and measured the stroke increase?

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shotgun

12-01-2004 10:48:25

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Re: 1955 JD 70 in reply to Ben Nichols, 11-30-2004 09:42:35

Yall on the 70 talk got any idea were 70 Lp piston can be found?

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G/MAN

12-01-2004 13:37:29

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Re: 1955 JD 70 in reply to shotgun, 12-01-2004 10:48:25

New? Used? Aftermarket? You might try contacting a Deere dealer and have them search other dealer inventories for NOS pistons.

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11-30-2004 16:43:28

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Re: 1955 JD 70 in reply to Ben Nichols, 11-30-2004 09:42:35

I sent my cam to robert,s back in two weeks i don,t know what it will do but looks real nice they seem like good people to work whith i hope it help,s reasanly price,s too 180.00 dangler wanted 400.00 i don,t know who,s better but i delt whith him be for and he is always double of every one else

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Mike S 806/H

11-30-2004 16:20:56

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Re: 1955 JD 70 in reply to Ben Nichols, 11-30-2004 09:42:35

I cut the head on my 70 down till it hit the eyebrows. I think it was around .230

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Old Joe

11-30-2004 14:48:28

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Re: 1955 JD 70 in reply to Ben Nichols, 11-30-2004 09:42:35

Hi Ben, I am in the process of rebuilding my JD 70 gas. I just had my head milled .125 and I do not forsee any problems with this amount. I have to send my cam out to be reground. I've been checking around and haven't decided where to send it yet. Where did you send yours and what did they tell you they could do for you?
Old Joe

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Ben Nichols

12-01-2004 09:40:55

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Re: 1955 JD 70 in reply to Old Joe, 11-30-2004 14:48:28

I am sending the cam to Roberts Carb Link cost is $165.00 plus shipping. You tell them what you've done to the engine and they adjust the grind for the engine mods. I talked with two shops that advertise in the Green Magazine and they both agreed on the .125 mill on the head although I've heard of people taking up .250 off. I also found out yesterday that aftermarket 70 pistons are not hi-compression but I was told you could have the rods lengthened to bump the compression. Anybody had that done for a JD 70 and how much do you add without going to high on compression.

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