Depending on the rarity of a silver dollar, cleaning it may decrease its worth. Older coins that have oxidized or collected a little dirt over the years are generally more valuable. However, if the coin is heavily circulated and of a common, more recent year, then cleaning it won't cause any harm to the value.
Place aluminum foil in a small shallow pan with the shiny side facing up.
Place the silver dollars in the pan.
Add ¼ cup baking soda and 2 to 4 cups of boiling water.
Allow the coins to sit for at least an hour before removing them and wiping them off with a soft dry cloth.
Apply a small amount of olive oil to a soft, non-abrasive clean cloth.
Rub the coin with the cloth and olive oil until it is clean and shiny, reapplying more oil if necessary.
Use a separate dry clean non-abrasive cloth to clean up any oil or residual debris from the coin.