Drilling Small Block Oil Drain-back Holes in Valley Area?

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dibbons

dibbons

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I just remembered today having drilled a series of drain-back holes in the '65 273 block that I ran in my bracket racer. They would have been placed between each pair of lifters in that little spot where a small amount of oil tends to sit and puddle. I also had painted the interior of the block with Rust-Oleum rusty metal red primer after the mods.

Now, I painted up the 340 block I am preparing (see photo), but this time I am going to forego the drain back holes. That was a little scary back in the '70's, I always wondered if I was weakening the center structure of the block (the holes were not very large).

I don't believe I thought of the idea of drilling the holes on my own, I must have read about it somewhere back then in the 1970's. Has anyone found a reference book or article that discusses this procedure? Anyone have photos of a block modified in this manner? I was just curious what was out there. Thank you.

340 block painted.JPG
 
dibbons said:
I just remembered today having drilled a series of drain-back holes in the '65 273 block that I ran in my bracket racer. They would have been placed between each pair of lifters in that little spot where a small amount of oil tends to sit and puddle. I also had painted the interior of the block with Rust-Oleum rusty metal red primer after the mods.

Now, I painted up the 340 block I am preparing (see photo), but this time I am going to forego the drain back holes. That was a little scary back in the '70's, I always wondered if I was weakening the center structure of the block (the holes were not very large).

I don't believe I thought of the idea of drilling the holes on my own, I must have read about it somewhere back then in the 1970's. Has anyone found a reference book or article that discusses this procedure? Anyone have photos of a block modified in this manner? I was just curious what was out there. Thank you.

View attachment 1715618718
Click to expand...


Why not just open up the standard drain back holes in the china valley with a die grinder, that's what I do to help the oil drain easier...
 
I believe I had done that type of drilling because that's what was said to be done. Wisdom now says to block holes and drain at very back or timing cover area so the oil does not fall onto the spinning assembly and rope power or froth the oil. To the best of my knowledge and remembering what I've read. And blocking the opening in the middle was good for 25hp? according to one Mopar magazine article.
 
I have no plans on any more grinding/drilling on this build, just curious historically speaking who/what/where this idea was sourced from back in the day.
 
You don't think the oil pooling around the lifter bores aids in cooling them do you? It just seems like an insignificant amount of oil to worry about to me...at least worrying about returning to the pan. How much do you think pools there? An ounce? Maybe two?
 
Point well-taken RRR, back when I was an inexperienced young buck, I followed along with most of the "tricks" I would read about in car publications and technical bulletins.
 
dibbons said:
I just remembered today having drilled a series of drain-back holes in the '65 273 block that I ran in my bracket racer. They would have been placed between each pair of lifters in that little spot where a small amount of oil tends to sit and puddle. I also had painted the interior of the block with Rust-Oleum rusty metal red primer after the mods.

Now, I painted up the 340 block I am preparing (see photo), but this time I am going to forego the drain back holes. That was a little scary back in the '70's, I always wondered if I was weakening the center structure of the block (the holes were not very large).

I don't believe I thought of the idea of drilling the holes on my own, I must have read about it somewhere back then in the 1970's. Has anyone found a reference book or article that discusses this procedure? Anyone have photos of a block modified in this manner? I was just curious what was out there. Thank you.

View attachment 1715618718
Click to expand...

Personally I grind that casting flash out of those holes in the middle of the lifter Valley. All that flash in there is just good for causing a crack.

Had a 273 that cracked from that flashing. Ruined a good block.
But that's just me and my personal opinion which I highly value.
 
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