Every so often, when working on a slant, I wonder why the Melling oil pumps have the "kidneys" in the cover. Most other brand pumps just have a flat cover. So I called Melling and asked. The tech guy, did not know, but said he would check and get back to me. He called me back yesterday, and said they help get oil to the back side of the rotor, and help to reduce the power required to drive the pump. Now you know the rest of the story.

PS: Melling is no longer making the high volume oil pump C66HV.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

From "History of Chrysler Corporation's Slant-Six Engine" (W.L. Weertman):

"Of interest, the original oil pump covers were flat plates. Later kidney shaped
cavities were added to the pump side of the covers. These were added to
improve the efficiency of the pump and to allow any water in the oil to freeze
without tying up the pump rotors."

"Later" means about 1965.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

If you put one of the kidney covers on out of postion you will not have oil pressure at idle. Yes, they are marked.

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Official Cookie and Mater Tormentor.

This might be a late follow-up to this post, but this is interesting: I was just wondering about this today. I was sent a pump from jhdeval (thanks!) for my engine rebuild and I'm trying to figure out if it's original Chrysler-produced, or an OEM aftermarket replacement. I'm told it's a hardened gear + it has the kidney-shaped cavities in the cover plate, but they're more rounded compared to the cavities of the new Melling I was going to install. It's too covered in caked-on oil to tell, but I haven't found any DPCD markings on it yet. It is a 6-bolt pump, similar in design to the original aluminum-bodied flat-cover pump off my '63 225, but it's made of cast-iron.

jhdeval - what engine/car was this pump from? Hoping the rotor frees up once I remove the cover: it's completely stiff right now and won't turn.

Once the cover and rotor are removed it will free up. I found that the oil gets pretty thick and prevents it turning free. That is why I suggested the mineral spirits as a soak. Even after clean the rotors are tight and require a bit of work to spin.

As far as what motor it is off of. That is a bit more of a challenge. I bought a motor back in January and the guy gave me a BOX of miscellaneous stuff which included that oil pump. The motor I bought was a late 60's motor but it had a pump on it already so the pump I sent you came off a different motor. I am pretty confident it is off a late 60's motor though. I ended up with 2 blocks and 3 oil pans all the oil pans are the same which means the "short snout" later design.

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

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slant six's RULE!
http://www.usajon.com

Interesting. Looks similar to the one I got from jhdeval, but I have yet to spy the CDPD mark on the cover, that I can clearly see on yours. Seems like there's variations in design. Yours has those square and hollow frame girders on the top and the side, whereas the one I got doesn't, plus yours has the oil sending outlet that has a more defined 'ridge' around it than mine. BUT, my aluminum factory original pump off my '63 225 does have them. Hmmm!

I don't think that is an 80s truck motor unless it is from a 1980-1982 truck or has been repainted. That looks like a dirty blue 70s motor to me. From 83-up slants in trucks and vans were painted black and before 83 the oil pumps had the flat oil pump cover.