Mystery gifts from oil pan.

That was my first thought also

 

I think somebody thought that engine was a wishing well, and they wished beyond the penny.

 

here is a picture of a wrist pin snap ring, so you will see that they are also used for piston wrist pins



Wrist Pin Locks: Different Styles and How To Install Them

 

Not that style. There are internal and external snap rings. The one in the OP is an external snap ring, meant to go on a shaft. This is an internal snap ring. They go inside a bore. Note the orientation of the holed tabs for the pliers.

 

Lifter? Do you have any repair history? I know nothing about these engines and this is just a shot in the dark.

 

also the "shoulder" which i did not catch previously.

but to be clear, snap rings (that require the tool with the "nubs"), can be used as wrist pin locks.

 

the penny was used to run the over head. i use to set the gap on my lawn mover coil with a paper customer tag. the paper one with the metal twisty tie ends