I have a 1990 240 with 300,000K. I had sign of coolant getting into the cylinders. A slight bit of white smoke at idle, but a massive amount of white smoke when engine got up to temp and accelerating up a hill, along with a massive amount of preignition/Pinging at the time of the massive amounts of white smoke.

I have removed the head. I see no obvious head gasket problem. I cant check the head for flatness until I clean it first.

How should I go about cleaning the head and not scratch or damage it?
How should I go about cleaning the block and piston tops without damaging them?

Pistons are pretty black. I could scrape a fair bit of stuff off. Should I leave pistons alone.

Could there be a crack in the head somewhere between a coolant passage and the intake valve passage. Maybe the crack opens up when the head gets hot?

Should I just put a new head gasket on and close it up? Any Advice?