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Sierra 18-4638 Marine Piston .015 Oversize Starboard Mercury Outboard

Manufacturer

Sierra

<p>For nearly six decades, Sierra has established itself as one of the marine industry's most trusted names in aftermarket engine and drive parts. Founded as a specialized marine parts manufacturer, Sierra has grown into a comprehensive supplier of replacement components, instrumentation, and accessories for both recreational and commercial boating applications. Operating from their 300,000-square-foot distribution center in Litchfield, Illinois, Sierra serves boat owners and marine technicians worldwide with an extensive catalog of parts engineered specifically for the harsh saltwater environment.</p><h3>Marine Engine Excellence</h3><p>Sierra's reputation was built on delivering precision-engineered internal engine components and drive system parts that meet or exceed OEM specifications. Their <a href="/7570-sierra-engine-gasket-set-5404">engine gasket sets</a> provide critical sealing solutions for inboard and outboard motors, while their <a href="/7570-sierra-engine-complete-assembly-15341">engine complete assemblies</a> offer comprehensive replacement options for major overhauls. Each component undergoes rigorous testing to ensure reliability in demanding marine conditions, from corrosion resistance to temperature cycling performance.</p><h3>Instrumentation and Monitoring Systems</h3><p>Accurate instrumentation is essential for boat operators to monitor engine health and prevent costly breakdowns on the water. Sierra's comprehensive line of <a href="/7570-sierra-gauges-200483">gauges</a> includes everything from fuel pressure and temperature indicators to voltmeters and trim gauges, all designed with marine-grade materials that withstand vibration, moisture, and UV exposure. Their <a href="/7570-sierra-tachometer-gauge-1488">tachometer gauges</a> deliver precise RPM readings critical for optimizing engine performance and fuel efficiency. Supporting these instruments, Sierra's <a href="/7570-sierra-gauge-resistor-47908">gauge resistors</a> ensure proper signal conditioning and accurate readings across various sensor types and engine configurations.</p><h3>Expanded Product Portfolio</h3><p>In 2022, Sierra significantly broadened its scope beyond traditional marine engine parts to encompass a wider range of boating accessories and even outdoor power equipment components. This strategic expansion brought established marine brands like Shields and Moeller under the Sierra umbrella, creating a one-stop resource for marine maintenance and replacement parts. The company now offers fuel systems, electrical components, battery charging solutions, and NMEA electronics alongside their traditional engine parts lineup.</p><h3>Quality Backed by Industry-Leading Warranties</h3><p>What sets Sierra apart in the crowded aftermarket marine parts market is their commitment to standing behind every component they manufacture. Their warranty coverage extends beyond simple part replacement—it includes shop labor, haul-out fees, towing charges, and related incidental costs should a warrantied part fail. This comprehensive protection reflects the company's confidence in their manufacturing processes and quality control standards. For boat owners facing repairs far from shore or mechanics working on customer vessels, this peace of mind is invaluable. Whether you're maintaining an outboard motor, rebuilding an inboard engine, or upgrading your boat's instrumentation, Sierra's decades of marine industry experience and commitment to quality make them a reliable choice for keeping your vessel running at peak performance.</p>

Part Number

18-4638
08/07/2036 10:00 AM
Sale Price

$118.41

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Usually delivered within 2 days

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Product Details

The Sierra 18-4638 is a .015" oversize starboard piston designed for Mercury outboard engines with 2-ring inline configurations. Engineered as a direct replacement for worn or damaged engine pistons, this oversize piston is used during engine rebuilds where the cylinder bore has been machined to restore a proper fit and seal.

Sierra Marine parts are manufactured to meet or exceed original equipment specifications, ensuring reliable performance and longevity in marine applications. This piston is the ideal solution for engine rebuilds requiring a .015" oversize starboard-side piston for inline Mercury outboards.

Key Features:

  • .015" Oversize — designed for use after cylinder bore has been honed or bored .015" over standard diameter
  • Starboard position — cylinder-specific fitment for multi-cylinder inline Mercury outboard engines
  • 2-ring inline piston design — matches OEM ring configuration
  • Manufactured to meet or exceed original equipment performance standards
  • Part of Sierra Marine's comprehensive internal engine rebuild component line

Sierra 18-4638 is a specialized rebuild component intended for use by experienced marine technicians performing powerhead rebuilds. Always verify bore measurements before selecting piston oversize to ensure proper fit and engine performance.

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