Years ago I owned a 1970 Satellite with a slant 6. I was changing the oil pump and each one I found was missing one hole on the body of the pump. I had to omit one of the mounting bolts, because it had 5 instead of 6 holes (if I recall correctly). Needless to say, the pump leaked exactly where that other mounting hole would have been drilled.
The material was there, just not drilled.
I have looked at several pumps since and the same thing.
Anyone else notice this or experience this?

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Check out the pump on the bottom right. It has only 5 bolt holes.....
:shrug:

is there any problem with drilling out the 6th missing hole?

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1964 Dart GT

No doubt it can be done, just wouldn't want to. If I am buying a new pump I would want it to be right.

Just seems bizarre that this important element was missed.

Somewhere along the line I guess some bean-counter figured out that you don't need 6 bolts to secure the pump- 5 would do well enough. I've seen engine blocks where the casting for that 6th bolt boss just wasn't there. So some oil pump manufacturers make 6 bolt, some make 5 bolt- either will work. You can drill out the 6th hole if it makes you feel better.

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63 Valiant Wagon
225 - 4 bbl

It's not a matter of making me feel better, it LEAKS right were that hole should be

Look at the body of the pump. Without that bolt, that's a large area at the bottom of the pump with no attachment.


.........So others on here came across that as well?

I've never had a leak at that location, and I've had a '79 block that was not cast at that location and was fine. That 'pocket' is just not used and was eliminated in later castings, hence the bolt hole delete. There are a few posts on here where Doc discusses this a bit.

I think if it's leaking at that point either the pump body is slightly warped, or the block casting where the pump mounts should be checked with a straight edge as well.

-D.Idiot

Things leak.... It happens try a new gasket, its been proven over and over again that 5 hole pumps work just as well..

Do a careful inspection on your gasket, to be sure you are getting coverage & gasket compression along the lower edge of the pick-up tube pocket.
Many replacement oil pump gaskets do not give complete coverage in that area.
I add an extra piece of gasket material to correct any problem area(s).
DD

Good advice, thanks. I noticed you don't use a 5 mounting hole pump.

I have used "5 hole" pumps (7/8 impeller) with good success but use the factory "die-cast" oil pump (5/8 impeller) on most of my performance engine builds.
I do this to keep the drive gear loads to a minimum.
DD