Page 4 of JE Pro Seal Catalog by JE Pistons

5 RING DIMENSIONS D-wall: A specification established by the Society of Automotive Engineers (S.A.E.) that dictates the radial width of a standard automotive piston ring by the use of the following formula; Bore diameter 22 radial thickness. (4.000" 22=.182") 5 7 9 11 10 6 1 2 3 4 8 1. Free Gap: The end gap clearance when the ring is not compressed 2. End Gap: The end gap clearance when the ring is compressed to the bore diameter 3. Inside Diameter: The inside diameter of the ring at bore diameter 4. Outside Diameter: The outside diameter of the ring at bore diameter 5. Ring Axial Sides: The top and bottom surfaces of the ring 6. Torsional Twist: The installed position of the ring due to a chamfered area on either ring side that helps the ring cross-seal 7. Ring Face: The section of the ring that contacts the cylinder wall 8. Back Clearance: Distance between the inside diameter of the ring and the back of the ring groove when the ring is flush with the ring land 9. Axial Clearance: The distance between the ring axial height and the piston ring groove width 10. Radial Width: The width of the ring in the radial direction 11. Axial Height: The height or the thickness of the ring in the axial direction RING TERMINOLOGY Barrel Face: Term used to describe the curved section of the ring that is in contact with the cylinder wall. Used only on top compression rings. Dykes: A step cut into a top compression ring that helps to direct gas pressure to the shaded area on the back side of the ring, improving ring to cylinder wall seal. Flat Face: Simple flat rectanglular shape Taper Face: Describes the angled face of the second compression ring that scrapes excess oil from the cylinder wall surface. Used only on second rings. Napier: A special hooked shape found on the underside of some second compression rings used to more efficiently remove excess oil from the cylinder walls. RING FACE SHAPES .182" .162" Piston Crown Top Ring Groove Second Ring Groove Oil Ring Groove Wrist Pin Bore Piston Skirt RING DIMENSIONS AND TERMINOLOGY Neutral: A term used to describe a piston ring that has no torsional bias or twist. Reverse Twist: An asymmetric change in the ring cross section causing the ring to twist downward (towards the piston skirt) that enhances the second compression rings oil scraping properties. Positive Twist: An asymmetric change in the ring cross section that causes it to twist in an upward direction (towards the piston crown) aiding ring sealing of the top and bottom of the ring groove. Positive twist is used only on top compression rings. Back-cut: Used to describe a compression ring that has less than S.A.E. standard D-Wall radial thickness. Back-cutting is used to reduce natural radial ring tension. In applications with tight top ring land to piston intake valve pocket clearance problems, back cut rings allow the rings to be moved up toward the top of the piston which improves combustion efficency and provides more power.

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