Wiseco SK1218 2-Stroke Pro-Lite Top End Piston Kit for Ski-Doo Rotax 503/521 73.50mm Bore

The Wiseco SK1218 is a precision-matched and balanced 2-stroke top end kit engineered for Ski-Doo snowmobiles equipped with the Rotax 503/521 engine. This kit brings the bore out to 73.50mm (1.50mm oversize) from the standard 72.00mm bore, displacing approximately 543cc, making it an ideal solution for overbore engine rebuilds requiring Pro-Lite forged piston technology.

Kit Includes:

• Forged Pro-Lite piston set — part #2373M07350 (x2)
• Ring set — part #2894LK (x2)
• Wrist pin — part #S513 (x2)
• Circlip — part #CW18 (x2)
• Top end gasket set — part #W5255

Key Features:

• Forged aluminum construction — forgings feature a condensed, aligned grain structure that delivers superior mechanical strength, impact resistance, and fatigue durability compared to cast alternatives
• Pro-Lite design — optimized strength-to-weight ratio for improved throttle response and reduced reciprocating mass
• Cast iron bore compatible — designed specifically for cast iron cylinder bores
• Precision matched and balanced — each set is matched for consistent performance across both cylinders
• USA-forged — Wiseco forges all pistons and tooling in-house, maintaining full control over every stage of manufacturing, from raw billet to finished skirt coating
• In-house dyno development — each design is validated through Wiseco's state-of-the-art in-house dynamometer facility

The SK1218 ships as a complete top end rebuild kit — no need to source components separately. This is an aftermarket replacement kit designed to replace OEM components. Note: Oversize pistons require professional cylinder sleeving or boring to 73.50mm prior to installation.