blis

Don't clean the sides of the piston, just a light wipe with methanol to remove any gum.

Heres my regular maintenance list for engines:

Pull down, Engine
Clean out all heat sink fins with a toothbrush to maintain best cooling.
Flush bearings of castor gum with good quality brake cleaner
Using plastics only clean out bearing grooves on crank and check conrod oil hole for crank pin
Carefully polish off the top of piston without going near the edges and polish head button, again careful not to touch the edges.
Polish and remove rust/oxides from crank, do not use petrol or harmful solvent on the crank in case you react with silicon in crank (if applicable)
If liner top is scratched or damaged, I place 2000 wet and dry on FLAT GLASS and use an old liner with after run oil to rub up the wet and dry so the brass acts like a lubricant and use oil to gently polish out any scratches in a figure of 8, do the same for backplate if needed.
Hand lube the entire engine without overdoing it
Use clean cotton, nothing abrasive and enjoy the experience.
It doesnt have to be shiny, just clean of oxide and residue that might harm combustion.


Sure there'll be many people that will argue against my method as being over the top or harmful, but I take special care where it's due to maintain compression, like never touching the inside of liner, edges of pistons, button and piston sides. The carbon on the piston sides would have worn away if it was tight.

PS: You piston looks fine, just a little cleanup as I noticed your fingers!!