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Yes, there’s a sort of countersink there. Should it be like that?

A small countersink is ok, that hole doesn’t look right now you have pushed the plug in further.

For future reference I use Loctite 648 on this type of plug and never had an issue. Although I don’t really like these brass plugs, found some steel ones on American eBay.

gs.davies wrote: ↑Mon Apr 17, 2023 6:17 pmI had a brass punch in the centre of it and I gave it a gentle nudge. It’s gone in another 3mm. I’ve measured as best I can the size. 13mm where the end of the plug is

With some basic schoolboy maths, it doesn't look good to me...

0.5" diameter = 0.25" radius of the plug, so the surface area is 𝛑 x (r^2) or roughly 0.2 square inches.

Let's say worst case the oil bypass opens at 100 PSI, that gallery plug has to hold at least 100 x 0.2 = 20 Lbs force.

I doubt the interference fit of 'a gentle nudge' is going to hold up for very long. Especially once the block warms up and the tolerances start to open up...

If it were me, I'd at least think about double stacking it with a solid plug immediately in front of that pressed one, file a flat on one side so it clears if you don’t want to grind the engine front plate, and then epoxy it in place with a liberal serving of JBWeld.

If you have a friend with a lathe you could even make the new solid plug stepped so it sits inside the cup of the current plug and bears on the front surface. It would look something similar to a short version of the 22H983 solid engine to gearbox dowel.

if your that worried .. why not make & fit an "exterior" sealed cover plate over the oil bung .. would give a sence of security when you are a long way from home