Grate pears; place in a large heavy saucepan. Add sugar and butter; mix well. Bring to a boil; boil gently 2 hours. Stir in pineapple; boil 5 more minutes. Spoon into hot sterilized jars, leaving 1/4-inch headspace. Remove air bubbles; wipe jar rims. Cover at once with metal lids and screw on bands. Process in a boiling water bath 10 minutes; set jars on a towel to cool.