This tractor has been made with a Briggs Vanguard and an Onan engine. You cannot interchange these two engines without major problems. The complete 16hp Onan/Linamar engine is no longer available for this. Use our 386447-Ingersol4018 Conversion Kit for these tractors. If you buy the 305447 or 356447 series of Vanguard engine you will likely have to change the flywheel fan and the shroud for it to physically fit in the tractor.