Probably depends on which 8hp engine, and which year or vintage is the riding mower.
My late good friend had Ford lawn tractors, and he went through a lot of engines and engine work. Don't recall which engines.
I've had good fortune with the old 8hp Kohler engines with cast iron blocks. In the process of rebuilding one now that was in my Dad's 1964 Deere 110. It was the same K181S that was in my 1968 Wheel Horse (which is still mowing and blading snow).
Any more details for us? Mower model number, serial number, and year; engine make, model and serial number?