This is what happens when one overtightens a plastic oil drain plug in a Tecumseh TVS engine.[1]
The hex is gone, and the remaining straight-threaded plug remnant will seep oil forever.
Fortunately, the plug remnant is not difficult to remove -- jab it with the tips of a pair of long-nose pliers, and you can coax it out. Here's the plug outside of the engine, along with what I mean to use to repair it.
That disc in back is a steel knock-out from an electrical box.
Key to this repair is squaring off the ragged end of the plug in the lathe, like so.
With that done, I can bore the plug remnant and the steel disc through 11/64" diameter to accept an 8-32 screw. With the disc lapped flat, the whole affair can go together with CA adhesive as a threadlocker, like so.
Add the o-ring, and the plug remnant is a functional plug again.
That made my day.
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Note:
[1] It wasn't me who overtightened the plug -- honest. The engine shown is one that I salvaged from an old wreck of a mower.
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