Block pic. What is this hole used for?

[Blue4x4]

Not my block, But can anyone tell me the purpose of this hole? I just finished installing my heads and realized that a portion of this hole is showing. I really don't want to pull the heads just to find out it's nothing. Thanks

[70c10swb]

knock sensor?

[matthufham]

good question, you're right about oil pressure.

[mjrmn]

WOW that is a good question-I just went thru my Chevy power catalog and cannot find that hole in any of the pics or descriptions.
Is the hole tapped for a plug?
Can you tell if it just stops at the bottom or if it leads to an oil or water passage?
I would think that if the head only partially covers it that it is probably nothing but I am not sure.
Hopefully someone else will have an answer for you

[jhow66]

For factory access for a drilled passage. Will be plugged. Almost impossibe to remove plug but no need to remove it.

[Blue4x4]

Thanks jhow66. I was able to look inside the hole with the head on and see an allen screw.

[Blazer1970]

Yup, it's a cross drill.

[hoser]

Originally Posted by Blazer1970

Yup, it's a cross drill.

Cross drilled to where? if its a oil passage the plug should be removed and the passage cleaned if the block was cleaned IE boiled or cooked because it could hold crap that could later be introduced into the oil system.

[Leonard1]

Hey guys, still pretty new here, but I'll give this a shot.

I think that is the access to remove the little plug that blocks the oil return passage. It looks like the plugs that go above the camshaft. When rebuilding a block, I always remove it, and the plug, and rod out all the old sludge. BTW, if you leave that plug out, you are bypassing the filter.

The SDPC catalog has a great diagram of this