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John Deere Tractors Discussion Forum
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WIll a 70 AF head bolt to a gas block?

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Joey

08-23-2004 09:02:51




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Hey guys..
Will an all fuel JD 70 hea bolt to a regular gas block?
Guy claims he has an AF tractor, but it has a gas block????

Thanks, Joey...




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WTW

08-23-2004 09:50:47




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 Re: WIll a 70 AF head bolt to a gas block? in reply to Joey, 08-23-2004 09:02:51  
Joey, A "70" AF head has the same bolt pattern as a "G" and is one bolt/stud less than a "70" GAS. So he either has a gas head or an AF block and head. The AF 70 head will not fit the 70 Gas block (different bolt pattern). DW



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buickanddeere

08-23-2004 11:47:41




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 Re: WIll a 70 AF head bolt to a gas block? in reply to WTW, 08-23-2004 09:50:47  
I ran into this problem with a 70AF that was hauled into Ohio from the Midwest. Didn't bother to negotiate any farther after seeing the pictures. Someone had pulled the all fuel block/head/manifolds/sediment bowl/valving and gasoline starting tank off it. And stuck enough gasser parts so it would sort of run. I called the tractor yard where it came from originally and yes they just happened to have everything for an all fuel 70 except the head that some tractor puller had just purchased. Little do these pullers know the 70 all-fuel head makes less power/flows less than the G head from Jerry's. The 70AF's larger combustion chamber makes it tough to get enough compression as well. Many hours of welding are required to fill them in.

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WTW

08-23-2004 12:48:38




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 Re: WIll a 70 AF head bolt to a gas block? in reply to buickanddeere, 08-23-2004 11:47:41  
Compression was never a problem on any of the applications I ever used these AF heads on as they were always on a engine with a 9.25 or more stroke and a power-block under them. I have never welded a head up or ever shaved a block or head to gain compression, always do it with pistons and rod lengths. Why loose all the integrity of the head or block by machining it away?? Just pencil out what CR you want to end up with and have the right piston and rod combination to make it all work. The AF head will make good power if you got all your ducks in a row. DW

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buickanddeere

08-24-2004 07:15:22




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 Re: WIll a 70 AF head bolt to a gas block? in reply to WTW, 08-23-2004 12:48:38  
The extra 2.25" of stroke and the 1/2" over bore adds a lot of extra swept volume to squeeze into the larger all fuel head. For a stock bore and stroke G/70 the piston will be so far ahead in the bore to get decent compression.That the spark plug will be seriously shrouded/obstructed.



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WTW

08-24-2004 12:55:31




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 Re: WIll a 70 AF head bolt to a gas block? in reply to buickanddeere, 08-24-2004 07:15:22  
Your right, If he is playing with a stock bore and stroke just as well leave a stock (flat) head on it as he not to serious of a puller anyway. Really won't gain any / noticeable HP increase over the single induction carburetor to even make a difference. On the old (early) unstyled A and B model tractors with the stock block and spark plug way back in the block, the trick is to modify the cylinder head to a Hemi head and not worry about obstructing the plug anymore. Been there and done that too, but the better option is to just go to a later block and get the plug far enough forward so it is not a concern anymore.

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