Brass plugs? Need advice

Hello brains trust,
Can someone please tell me what these brass plugs, if they are plugs, are for?
I’m wondering if it would be ok to remove them in order to paint the block.

Not 100% sure but think they are just plugs , holes left from machining the oil way’s out .
I have taken one out , to add my mechanical Oil pressure gauge .
No reason why you can remove them to paint your block !

Bear in mind that there are copper washers involved so annealing them before reinstallation is a good idea…and yes, they do seal the drillings made thru to the main bearings from the main oil gallery.

I’ve never understood exactly what they’re for. The ones in the front and rear had to be there so the oil passage could be drilled. The side ones are often used for mechanical pressure gauges or oil coolers but I can’t think of 6 possible devices that might want to tap off the main oil supply. Maybe they were used during the long drilling process to inject oil for bit cooling?

In any event, they added them to every block, and yes you can remove them. Unless you’ve drained all the oil some will drip out as they tap directly into the same main oil path that feeds the filter though.

Erica, somehow the oil needs to get from the oil gallery to the bearings and those drillings had to be made from the outside and the drillings had to be plugged. 7 drillings for 7 main bearings (one is behind the filter). Yes, they can be removed, then everything has to be cleaned thoroughly (!) and the copper washers have to be annealed by heating them so they just glow and then leaving them until cool. They will change colour but that does not matter.

Ahhh, yeah that makes sense! That’s why 6. So they’re drilled all the way through to the center, not just into the oil passage.

7 actually (and the last one is drilled from both sides of course), and there is dirt inside that collects where the drilling ends; it is a dead end forming a little pocket and another drilling goes into there, so the pocket is a bit of a trap for some particles :slight_smile:
I cleaned them out with some round brushes. If the crankshaft stays in place I wouldn’t take them out.

Here you can see where the drillings go:

Note the tape on the lower photo, I was anxious not to get any dirt inside; and I painted over the bolts, good choice it seems. They were painted before.

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Hi, I have a NOS 4.2 short stud replacement (unstamped) engine block. The oil galley plugs were painted the same low gloss black as the block. Paint right over them.

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Six drillings just go to the center to supply oil to the main bearings and through the crank to the rods, and the seventh at the rear which supplies the rear main also goes through to the other side where it supplies oil to the small tube and on up to the head.
Drillings have to be done from the outside, which is why they have to be plugged afterwards.


On their lost foam-cast blocks, Saturn cast-in the oil passages. They figured it saved them millions of dollars over the life of the engine’s production run.

Back in the day (maybe still today) it was bad practice to drill out a cast bore, at least that’s what one of my 60‘s books says. But here it’s a blind bore so the way they did it it has to be done from outside.

The 7th is drilled from both sides. Not that it matters of course but the reason is the same. Can’t start the drill if it’s not at a right angle to the surface and it wouldn’t be, inside the bearing. Could be done, but then the block would be heavier/ weaker/ whatever.

They‘d have to do a good job about the remaining casting sand. Submerging everything in glyptal at least. That long gallery must have been very expensive to machine.

They plug end of the drilling from the main oil galley to main bearing bores. The other (open) end of the drilling is indicated by the red dots in the photo.