Any chance Bad Tooth of giving us a bottom view of the removed glow plug? From the photos you posted, I agree with the others on this thread in mentioning a serious Foreign Object Damage happened to your engine. In working in the engine maintenance field, I have seen this sort of internal damage before when spark plugs, and valve heads break during engine runs. Since you mentioned that the glow plug did not have an idle bar, I do not feel that the glow coil section could have caused that much deep metal damage. It is possible to clean up the cylinder head, but I would replace the rod, sleeve, piston and ring. The mention of a little rust on the bearings gives rise to just purchasing another engine as adding new bearings( why take a chance with the new parts)would make the repair cost in the ball park of a new engine. From a repair situation, it is not impossible to smooth out the pistion and cylinder head, and just replace the piston ring. How well the engine would run is an unknown.

Let us know what you decide to do, and how well the engine runs if you decide to repair it.

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retired aircraft mechanic