You have what is called an L head or flat head. Have to remove the head to access the valves. and remove the small cover on the side of the engine which maybe behind the muffler to access the valve springs to check clearance. Adjustment are made by removing the valves and grinding the valve stem to get the proper clearance.
One the OHV that you refer the valve clearances will open up. On an L head they will close to the point of holding the valves open slightly. But that wear resulting in the valve clearances closing takes years in most cases, And I mean years. I just did 2 L head valve jobs on 3 and 5 HP Briggs a couple of weeks ago. The newest engine was from the 70's