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G John Deere Head Rebuild Questions

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Brandon

09-10-2002 18:11:10




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I have a '51 G John Deere that is powering out in the 6500# class when the hitch is at 20". It has high-top pistons in it and dynoes 52 HP. What can I do to the head to give it more power? Can I take the stock head and have it milled down into a flathead or are they made different? Will I have any clearance problems with anything? How much does the pushrods have to be shortened? What can I do to the valves? What is the best type of manifold for it that I can get aftermarket without having to put a used one on it? Where should I have the cam sent to to have reground? Thanks for the help.

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lynn

09-11-2002 17:51:56




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 Re: G John Deere Head Rebuild Questions in reply to Brandon, 09-10-2002 18:11:10  
Brnadon..one thing you can do is take the rods and cut and weld some a rod ends on them..same wrist pin size and not too expensive..add somewhere around .500 inch and you will end up with 8.5 to 1..have to measure to find out for sure..lynn



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burns

09-11-2002 17:02:48




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 Re: G John Deere Head Rebuild Questions in reply to Brandon, 09-10-2002 18:11:10  
Not sure exactly if you are looking for a simple modification or if you are willing to do a more extensive tear down. I personally have a Dengler cam but less money could be spent with Robert's. I can't say one way or another that the Dengler cam is better to justify the extra money or not. I am very pleased with results. 195psi and 70hp at 540.
Prior to my current engine setup. I had 1/8" shaved off the factory cyclone head. I shimmed my rocker arm assembly to compensated for the shorter head. As a back up, I have taken off another 1/8" but will probably end up shortening the push rods if that day ever comes. Call Keith Merfeld regarding filling the intake pocket with weld and eliminate the restrictive air flow of the eye brow all together.
A completely reworked flat head will cost you about $1000 (valves, seats, porting, and pinning)

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GPULLER

09-11-2002 09:59:16




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 Re: G John Deere Head Rebuild Questions in reply to Brandon, 09-10-2002 18:11:10  
My 51 G is .090 over w/M&W's stoke stroke and stock cam. It also has the late head, its ported in the bowl area below valves. Stock valves were back cut and given a 3-angle valve job. Also an 1/8 inch was cut off the face. The "eyebrows" on the intake vales are flush with face of head. I didn't want to cut up the pushrods so I made aluminum spacers to put between rocker shaft and head. I also port matched the stock all-fuel manifold to the head and manifold to the stock Big Nut carb. With this head cranking pressure is 135psi makes 58hp. I use the all-fuel manifold because its stock and I pull in a stock class. I have asked other people if one of Jerrys manifolds is an improvement over stock but everybody says that there is not much improvement on a farily stock G. I have a JD gas manifold also, and sometime when I have $150 burning a hole in my pocket I'll buy a Jerrys manifold and see which one makes more power. For the cam, call Roberts carb in Spencer IA 712-262-5311 he can give you more info. From what he has told me people see anywhere from 5-7hp. He knows what he's doing I put his demo Super 51 carb on my G for a test and picked up 5hp. Too bad had to send back. Hope this helps and gives you some answers.

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Jack

09-11-2002 12:21:14




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 Re: Re: G John Deere Head Rebuild Questions in reply to GPULLER, 09-11-2002 09:59:16  
A friend of mine has a 50 G with M&W high comp pistons at 100 psi per hole,he is turning out 55 hp.My 53 G has 110 psi per hole and is putting out 52 hp at 540 pto rpm.The only difference in our two tractors is the manifolds.I have the older style gas manifold on mine and he has a propane manifold on his.I was told that a propane manifold will help as much as three or four hp over the old style gas manifold.Hope so cause I bought one.Now I just have to get it put on.I was also told not to polish the intake but I could do the exaust.

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G Wally

09-11-2002 14:30:57




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 Re: Re: Re: G John Deere Head Rebuild Questions in reply to Jack, 09-11-2002 12:21:14  
Were did you get the propane manifold? What is the difference between your JD gas manifold and the new one? I didn't know that there was a propane manifold for a G.



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Jack

09-12-2002 04:42:02




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 Re: Re: Re: Re: G John Deere Head Rebuild Questions in reply to G Wally, 09-11-2002 14:30:57  
I ordered it from Bob's Triple G service.Here is his his number 716-542-3175.The gas manifold I currently run,in the back of the intake the fuel-air mixture hits the back wall and then sharply goes down into the head.And it also is right against the heat of the exaust too.On the propane manifold the exaust and intake are almost totally seperate making a cooler mixture and the propane manifold has a better flow.Later,Jack.

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cwj

09-10-2002 21:03:41




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 Re: G John Deere Head Rebuild Questions in reply to Brandon, 09-10-2002 18:11:10  
i would take your stock head and have it ported and shaved about 20 to 40 thousandths and have bigger valves and seats put in it. that should make a nice difference. going to the right machine shop someone who does high performce work would probably be the best they should be able to tell you what size valves will fit in the head.as far as the cam goes the place were i have sent mine in the past is Reed cams they seem to do a pretty good job i have there phone# if you want it.you should come out with 10 or more hp deppending on how far you go with the head and cam you might need to go with a thinker head gasket but then it depends on how much lift is added to the cam and how much is shaved from the head.i'm not sure about the manifold i hope i was helpfull i dont have JD's but i figured i would try to help.

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JDGnut

09-11-2002 19:49:41




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 Re: Re: G John Deere Head Rebuild Questions in reply to cwj, 09-10-2002 21:03:41  
.020-.040.. won't make a big enough difference to see... most cut about .250 off the stock head... just depends on how many time it has been cut on before... Valves in the flathead can be 2 7/8.. have to modify the chamber a little so the valves will clear or you'll break a rocker arm...
JDGnut



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JDGnut

09-10-2002 19:34:34




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 Re: G John Deere Head Rebuild Questions in reply to Brandon, 09-10-2002 18:11:10  
The flathead is off a Unstyled G.. U can mill a stock/styled head, but not to the point of a flat head.. The flathead has No combustion chamber in the head.. The flat head is about 3/4in shorter than the styled head.. The studs will have to be changed or you can use washers. And change a few little things.. pushrods, exhaust pipe, intake pipe.. The head.. the usual stuff.. ported and bigger valves.. on the unstyled heads you can have it pinned behind the chamber to keep it from flexing..
JDGnut

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