Piston as seen using an endoscope

[nsa]

...as seen down the spark plug hole. The endoscope is just a £10 eBay job. I took more pictures but unfortunately this is the best. All four pistons look like this.



The engine runs fine and compression etc is good and it doesn't use a lot of oil, but I assumed the pistons would be shiny clean. Is the wet patch oil sucked up past the piston rings, and is it worth trying to do something about the brown coating?

[nsa]

Great. Thanks. I'll check if the same wet patch appears under the other injectors and investigate cleaning them.

[nsa]

Thanks again. I appreciate people taking the time to look. The spark plugs had a nice beige glaze to them as well.