Andreas Syversen Skartlien

My grt grt grandfather was Andreas Syversen, from the Skartlien farm near Torpa in Oppland. He was born in 1835, in Land, and by 1869-70 was in Chicago, Illinois as a machinist. I have been trying to find out just when he came to America but have had no luck so far. I think he was possibly still on the farm in 1863 when his father died because I found his name listed as being at a nieces baptism that year. I don't find him leaving the parrish. He had to train as a machinist or model maker at some place--I thought maybe Oslo, before coming to America. He was single until 1871. The closest possibily I have is Andreas Martin Syversen leaving Oslo in 1869 going to Milwaukee. However his age is wrong, the Martin makes no sense, and they have him down as a sailor or deckhand. So my question is: does anybody have any ideas where else to find out when he came over? Any clues will be deeply appreciated. Thanks.