{"product_id":"sierra-18-3921-standard-bore-piston-ring-set-for-mercury-v-6-105-jet-135-150-hp-outboards-2-5l-replaces-oem-39-93481a12","title":"Sierra Piston Rings 18-3921 for Mercury Marine V-6 135-175 HP, 3.125 Inch Standard Bore, Replaces 39-93481A12","description":"\u003cp\u003eThe Sierra 18-3921 is a piston ring set engineered for Mercury Marine V-6 outboards in the 135-175 HP range fitted with 3.125 inch standard-bore pistons. Sierra manufactures its piston rings to match OEM dimensions and tolerances, giving a factory-correct seal between the piston and cylinder wall for proper compression and oil control during a rebuild or piston replacement. This ring set is used with the 3.125 inch standard bore piston application on this engine family and applies to both the port and starboard cylinder banks, since the ring specification is identical for both sides at this bore size (only the piston part numbers differ by side, not the ring set).\u003c\/p\u003e\u003cp\u003eThese rings are a direct cross-reference to Mercury Marine OEM part number 39-93481A12, so they install using the same ring gap and groove specifications as the original equipment rings. They are sold as part of Sierra's line of Mercury outboard 2-ring inline piston components, intended for engine builders and mechanics performing a top-end rebuild, re-ring, or piston swap on a compatible V-6 outboard powerhead.\u003c\/p\u003e\u003ch3\u003eSpecifications\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Sierra\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer Part Number:\u003c\/strong\u003e 18-3921\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCategory:\u003c\/strong\u003e Mercury Outboard 2 Ring Inline Pistons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBore Size:\u003c\/strong\u003e 3.125 inches, Standard\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEngine Fitment:\u003c\/strong\u003e Mercury Marine V-6, 135-175 HP\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOEM Cross Reference:\u003c\/strong\u003e 39-93481A12\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUPC:\u003c\/strong\u003e 030999621665\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeight:\u003c\/strong\u003e 0.06 pounds\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePackage Dimensions:\u003c\/strong\u003e 8 x 6 x 4 inches\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFitment\u003c\/h3\u003e\u003cul\u003e\u003cli\u003eMercury Marine V-6, 135-175 HP, 3.125 inch bore, Standard size, port and starboard cylinders\u003c\/li\u003e\u003c\/ul\u003e\u003ch3\u003eReplaces (OEM)\u003c\/h3\u003e\u003cul\u003e\u003cli\u003e39-93481A12\u003c\/li\u003e\u003c\/ul\u003e\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eWhat engines does the Sierra 18-3921 piston ring set fit?\u003c\/strong\u003e The Sierra 18-3921 fits Mercury Marine V-6 outboards rated 135-175 HP that use a 3.125 inch standard bore piston.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs the 18-3921 for the port or starboard cylinder bank?\u003c\/strong\u003e The 18-3921 ring set applies to both the port and starboard cylinders on the 3.125 inch standard bore V-6 application, since the ring specification is the same for both sides; only the piston part numbers differ between port and starboard.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat OEM part number does the 18-3921 cross-reference?\u003c\/strong\u003e Sierra 18-3921 cross-references Mercury Marine OEM part number 39-93481A12.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat bore size are these piston rings sized for?\u003c\/strong\u003e This set is sized for a 3.125 inch standard bore, with no oversize (overbore) adjustment.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow much does the 18-3921 piston ring set weigh?\u003c\/strong\u003e The Sierra 18-3921 weighs 0.06 pounds.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eAre Sierra 18-3921 rings a genuine OEM part or aftermarket?\u003c\/strong\u003e The 18-3921 is a Sierra-manufactured aftermarket part built to the same specification as Mercury Marine OEM number 39-93481A12.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use the 18-3921 rings for a re-ring without replacing the pistons?\u003c\/strong\u003e Yes, the 18-3921 is a piston ring set intended for use with existing 3.125 inch standard bore pistons on the compatible Mercury V-6 135-175 HP application.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat category of engine components does the 18-3921 belong to?\u003c\/strong\u003e Sierra lists the 18-3921 under its Mercury Outboard 2 Ring Inline Pistons category.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes the 18-3921 work with an overbore piston?\u003c\/strong\u003e No, the 18-3921 is specified for the 3.125 inch standard bore only; oversize applications use a different Sierra ring part number.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is the UPC for the Sierra 18-3921 piston ring set?\u003c\/strong\u003e The UPC for the Sierra 18-3921 is 030999621665.\u003c\/p\u003e","brand":"Sierra","offers":[{"title":"Default Title","offer_id":48988170256603,"sku":"SIE-18-3921","price":40.14,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0839\/7586\/4539\/files\/18-3921__46568.1722381689.500.750.jpg?v=1785188379","url":"https:\/\/www.goodvibesmarina.com\/products\/sierra-18-3921-standard-bore-piston-ring-set-for-mercury-v-6-105-jet-135-150-hp-outboards-2-5l-replaces-oem-39-93481a12","provider":"Good Vibes Marina","version":"1.0","type":"link"}