I had my engine apart and after putting it all back together I saw this small bowl like piece and I hope it is not important. I have a Toro 1438z. https://i.ibb.co/KV4bZBD/20190516-002213.jpg
Sorry to say, that part is important. You should have two of them. They go over the end of the valve stem and provide a surface for the rocker arm to ride on. When you find the other one fix is not hard. Remove the valve cover, loosen the rocker arms, install these caps and then you must reset your valve clearances.
