Re: Mark IV Big Block Oil Pumps
Patrick-----
Yes, in fact Mark's pump is what got me started on this quest to verify the specifications on the 65-66 Mark IV oil pumps. I was surprised to learn that his pump had the 1.30" gears as I thought that all Mark IV except ZL-1 used the 1.15" gears. George Wright had this pump with the same body and cover casting numbers as Mark's original pump. He sent it to me and I confirmed the internal specs.
I have every reason to believe that Mark's pump is original to his engine.
Is it possible that GM used the same 3860370 body casting for pumps with different length gears? Yes, I suppose it's possible but I highly doubt it. I know of no other case in which the casting used for a Chevrolet oil pump was not specific to a particular internal configuration, including length of gears.
Patrick-----
Yes, in fact Mark's pump is what got me started on this quest to verify the specifications on the 65-66 Mark IV oil pumps. I was surprised to learn that his pump had the 1.30" gears as I thought that all Mark IV except ZL-1 used the 1.15" gears. George Wright had this pump with the same body and cover casting numbers as Mark's original pump. He sent it to me and I confirmed the internal specs.
I have every reason to believe that Mark's pump is original to his engine.
Is it possible that GM used the same 3860370 body casting for pumps with different length gears? Yes, I suppose it's possible but I highly doubt it. I know of no other case in which the casting used for a Chevrolet oil pump was not specific to a particular internal configuration, including length of gears.
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