Is it safe to clean pistons (BMW part numbers: 11251338333, 11251338334, 11251338335) in a household ultrasonic cleaner using a 50/50 solution of warm water and Simple Green? The approximate duration of the ultrasonic cleaning would be 20 minutes. Next would be a nylon bristle brush (if necessary), rinse with hot water, dry, and temporary protective coat of oil to prevent corrosion. Are there any special coatings or surface finishes that might be harmed?
If you remove the rings, piston pin and circlips (everything that's ferrous) then there should be no harm in cleaning the aluminum piston any way you choose. Detergents are most likely pH "basic", so you don't want to leave aluminum pistons soaking for a week, but for an hour or 2 should be fine.
There's no need to coat the piston with anything becasue dry aluminum is fairly inert.
Actually, hot soapy water is regularly used on engine parts more often than one might suspect. To my mind, it's the best liquid to use when honing cylinders due to its ability to remove the abrasive material that's cast off. That same reason also makes it highly suitable for cleaning engine parts where any exploded engine debris or bead blast media might be present. Solvents don't dislodge foreign materials nearly as well as detergents do.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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