Captain, The white ring is made out of nylon and is used for the mechanical advance the Brisons used to come with. It is riding on the crankcase. Two inside clip rings keep it in place. There are two grooves in the case for the rings. The nylon ring can be fixed in position for use with the ignition modules with electronic advance. I’ll upload an image of one of the engines that has been changed over and you can see that the pushrod to the ring has been removed.
