So i got two pistons in my 351 C, It's bored 30 over and I have found so far that i don't have to file any rings yet. THe gaps all fall within spec's..but! I noticed when i took a piston out, to check on things, that the spaces your suppose to leave between the ring ends moved. I cranked the engine over by hand only twice to spread oil. Rings (End Gaps) were further apart, none overlapping however. So why set them! i would think while the engine is running that the rings will travel around the piston never staying in one place forever, or am i wrong?