Sorry John my .50 is brand new, I just broke it in, when I saw the discussion I decided to see if I had an ABN or a Dykes ring equipped engine. It was then that I noticed the ring ends were in the center of the rear intake port. The engine runs great. As my old Italian neighbor that I grew up beside would say, I mak-a you veddy confuse, so sorry. I learned a lot about oil well pump engines when I was quite young from those old guys.