Some sample data. You could use a character vector, but I'll use a data frame to match your example:
df <- data.frame(Manufacturers = c("Ducati,Diavel", "Honda,Goldwing",
"BMW,R1200GS", "Harley-Davidson,Fat Boy"),
stringsAsFactors = FALSE)
Use strsplit() to separate the strings. Note that it requires a character (not a factor) vector. Strsplit() returns a list object:
list <- strsplit(df$Manufacturers, ",")
Transform the list into a data frame and set appropriate column names:
library("plyr")
df <- ldply(list)
colnames(df) <- c("Manufacturer", "Model")