Somewhere I had this piece of literature from Kohler that described the differences...someday I need to find and scan that. From memory, besides the addition of full pressure lube to the cam, crank mains, and rod bearings, and oil filter provision, they changed some of the stiffening ribs in the case halves to strengthen them, went from gasket to RTV for barrel to case joint (this may have occurred later but I do know I have not seen a Series I with anything other than a gasket, or Series II/M18 with anything other than RTV), plastic oil fill tube/cap instead of a pipe plug, and maybe plastic flywheel screen, too.Thanks. Do you know other changes beside the oiling system?
You were correct the barrels will interchange. Got the series 2 together and running today. Everything seems to be doing as it should after replacing fuel pump,starter solenoid,rebuilt PTO, replaced PTO switch,coil,plugs, condenser,and driveshaft couplings along with a few more pieces.Theoretically they should. Just make sure if the cylinder had a gasket between it and the case halves to use a gasket, or RTV if it had RTV. I think that change occurred when they went from Series I to II, among other things.