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JD70 Compression

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ToddF

05-22-2001 14:12:55




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I have a JD70 Gas that comes up short at the far end of the track.(Well..."far" being a relative term;)). The tractor is bone stock with the exception of the chrome exhaust pipe, but even that is just sleeved over the stock muffler. Will shaving the head increase compression or are there aftermarket heads available and where can I get one? Or is there another head option that works on this tractor to increase compression. If not can the compression be increased without stroking? I don't want to cut the block; I may want to increase the stroke in the future. I'm exploring different possibilities so I'd like to hear what you all might have to offer. Even if I don't have many options with this tractor, I still have a ball hooking on to the sled. ToddF

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G Taylor

05-23-2001 21:25:37




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 Re: JD70 Compression in reply to ToddF, 05-22-2001 14:12:55  
LP pistons, LP manifold, after market cam, dry air filter conversion,msd ignition to partialy compensate for the sparkplug being placed on the edge instead of the center of such a large combustion chamber, straight stack. Don't waste $ on a 125 thou overbore if the cylinder walls are straight. The displacement increase with a 45,90 or 125 overbore isn't noticable. Even stock a 70G rowcrop should spin set of 15.5x38 Firestones 23 degree in the 6500lb class on the stickiest of tracks in 1st gear ( 2-1/2mph).

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Jack

05-23-2001 08:02:58




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 Re: JD70 Compression in reply to ToddF, 05-22-2001 14:12:55  
Hey Todd,I have a 56 70 with.125 over aluminum Clevite pistons and no shaved head and still spin out easily in 7000lb.class.If I had to do it all over again,I would have cut.125 thousanths off the head too.I got a 52 G I just got back together this week and I had .150 thousanths taken from from the head and it sure sounds healthy.I got to hook it up and see.If it out pulls my 70 it will have it's hands full doing it.Email me and I can tell you more about it,and good luck to you.Jack(TN).

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Rich

05-22-2001 20:31:23




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 Re: JD70 Compression in reply to ToddF, 05-22-2001 14:12:55  
Todd: My brother and I have redone a few tractors, deeres and ollies.The ollies are the open class pullers,we use the deeres in the more stock classes,thats were they really shine.We rebuilt and restored a 70,we cut the head some,and installed a set of high domed pistons in it.I believe the cranking pressure was about 160 pounds.had to run good fuel but we always had more than enough power. Got the pistons from hinrichs repair nice guy to deal with,decent prices too. We are working on tweaking a 70d std.at the present time, Next project is my 60.Heres the # for hinrichs 815-778-1900 hope this helps, Rich.

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al

05-22-2001 19:45:47




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 Re: JD70 Compression in reply to ToddF, 05-22-2001 14:12:55  
Merfeld weld rods for different stroked tractors.You could have him lengthen a set for you to increase compression. Omne problem would be that the rings would be traveling in new territory any ridge would be a nono. Or Have the tops of your alums pistons built up with weld.I see 70's with 200+ compression.



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Eric

05-22-2001 17:36:03




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 Re: JD70 Compression in reply to ToddF, 05-22-2001 14:12:55  
Yes shaving the head will increase your compression but I doubt if it will increase the compression enough to make the difference you need. I also have a 70 that has 75 psi cranking pressure. I have not checked into it more deeply but 75 sounds about right for a stock tractor. If you would like to dig into the engine, M&W style aluminum pistons can give you higher compression and more power. My brother pulls a '51 G, which is very similer to our 70's. His is equipt with M&W pistons. when he shaved his head .100" he increased his cranking pressure from about 100 psi to around 120 psi. He may have picked up 2-3 horsepower in the process. From my experience a 55 horsepower 70 John Deere if equiped with 15.5 x 38" tires should spin out in 6500# and 7500# on almost any track. I hope this helps.

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oldtimer

05-26-2001 07:05:52




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 Re: Re: JD70 Compression in reply to Eric, 05-22-2001 17:36:03  
How far can you mill a "g" head PAST the eyebrow without getting that area too thin?thanks



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G Taylor sigh, apples oranges again

05-26-2001 19:26:24




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 Re: Re: Re: JD70 Compression in reply to oldtimer, 05-26-2001 07:05:52  
Better off with LP or custom pistons. The thinner the casting the more likely to flex/crack & leak.



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