JD 70 Exhaust Manifold Valve

Blksmok

Member
Anyone know what the difference is in the exhaust manifold valve for a 70 gas vs. a 70 all fuel? Two different parts numbers and the all fuel valve (A4841R) shows as obsolete on JDParts.com. I don't want to damage the existing one during removal in the one piece manifold unless I have a replacement. Thanks!
 
(reply to post at 14:31:47 11/29/12)

Bruce, it's been years since I had two side by side to compare, but if I remember correctly, the all-fuel valve is close to the same port size on both flow through and by-pass as compared to the gas. The gas one has quite a difference in flow-through compared to by-pass. I think because they wanted the all-fuel to be hot versus hotter all the time, where as the gas needed to be REALLY cooler on hot weather.

I believe you could modify a gas valve to be an all-fuel valve if you wanted to grind and mill, if you had a broken all-fuel valve to go by.
 
Frank..I can't remember exactly what the heat exchanger valve looks like on a 70 gas. The all fuel valve is the same shape and dimensions (I think) but in addition to the large rectangular opening that routes the exhaust gas from the flywheel side cylinder to the front of the manifold where the carb bolts to...there's a circular 3/4 inch opening that routes some exhaust gas at the same time to the back side of the manifold. Can't recall if the gas manifold valve has that small hole (???) This 70AF is a "project" that has an interesting history...otherwise I wouldn't be trying to resurrect it. It started it's life in Montgomery, Alabama and somehow found it's way to Wisconsin. Surprisingly, I have a 70 diesel with the same lineage. Wonder if these were "dealer swaps" due to them not selling in Alabama (???)
 
(quoted from post at 21:25:29 11/29/12) ... This 70AF is a "project" that has an interesting history...otherwise I wouldn't be trying to resurrect it. It started it's life in Montgomery, Alabama and somehow found it's way to Wisconsin. Surprisingly, I have a 70 diesel with the same lineage. Wonder if these were "dealer swaps" due to them not selling in Alabama (???)

Wow. Could be.
 
I use a 4" grinder and split the old manifold and then hit it with a hammer and it will fall out. Be carefull not to grind too deep.
 
(quoted from post at 13:18:30 11/30/12) I use a 4" grinder and split the old manifold and then hit it with a hammer and it will fall out. Be carefull not to grind too deep.

So you automatically sacrifice the old manifold? On a A/F 70 I wouldn't think that they were all that easy to replace in today's market.
 

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