It's a four stroke single cylinder. factory water cooled. Come from an older Polaris 500 scrambler or Sportsman ATV, try to find one that is the HO version, they have more power. Usually can find engines and accessories on ebay. Its a dry sump engine and to fit behind the seat without modifying the frame, it has to be rotated backward about 100 degrees. You will have to modify the intake manifold to level the carburator. I don't think there is an easier repower than this. Bonuses are no ringa ding ding sound, starter never wears ou,t never burn up pistons and a realy good clutch . Good Luck, I think you'll like it.