https://www.yourmechanic.com/services/oil-is-leaking-into-spark-plug-well-inspection

These rings are set in grooves in the piston and help scrape excess oil from the cylinder walls and prevent oil from getting into the combustion chamber. If these ...

https://mechanics.stackexchange.com/questions/11267/are-oil-puddles-in-cylinder-head-normal

If you are suggesting there was oil inside the head where the valves/cam(s) are located, this would be perfectly normal. If you are saying the oil ...

https://www.freeasestudyguides.com/compression-test-injecting-oil.html

If the cylinder's compression is found to be below specifications, oil is injected. Introducing oil into a cylinder with worn piston rings increases the cylinder's ...

https://www.ms-motorservice.com/en/technipedia/post/piston-damage-and-causes/

Overheating due to combustion defaults; Bent/blocked oil injection jet ... Piston protrusion too great; Excessive remachining of the cylinder head sealing surface  ...

https://www.quora.com/How-can-oil-enter-the-combustion-chamber

If piston ring worn out, sealing between piston and cylinder is not proper. And the oil which is carried by piston crown remains on cylinder wall.

https://www.youtube.com/watch?v=ph9QsO11cFA

Mar 12, 2015 ... Not burning oil... ... Oil on top of piston. choochootrayn .... Removing Carbon From Piston, Cylinder Walls, and Block Deck - Duration: 14:23.

https://www.youtube.com/watch?v=Wadmzv1Vs0Q

Mar 16, 2016 ... They keep combustion gases from entering the crankcase, oil from the ... and they aid in heat transfer between the piston and the cylinder walls.

https://www.ifixit.com/Answers/View/115499/Why+is+there+oil+in+the+spark+plug+well

If the gasket is not sealed around the spark plug well it will leak oil into that area. ... Oil gets inside the tube and causes cylinder misfire.

https://haynes.com/en-us/tips-tutorials/5-things-go-wrong-pistons-and-how-prevent-them

Piston rings eventually start to wear and the seal between the piston and cylinder is no longer air tight. As a result, oil makes its way from the crankcase past the ...

https://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Piston%20and%20Piston%20Rings.htm

Piston rings seal the combustion chamber, conduct heat from the piston to the cylinder wall, and return oil to the crankcase. Piston ring size and configuration ...