Wiseco 4971M09000 Forged Piston Kit 90mm Bore 10.5:1 CR for Triumph Bonneville

The Wiseco 4971M09000 is a forged piston kit engineered specifically for the 904cc Triumph Bonneville parallel-twin engine. Featuring a 90.00mm bore and 10.5:1 compression ratio, this kit is a direct-fit performance upgrade designed to meet or exceed OEM standards for reliability while delivering the added strength benefits of a forged aluminum construction.

Wiseco forges, machines, and assembles every piston at their facility in Mentor, OH, ensuring strict dimensional tolerances and consistent quality. Each piston is a dedicated forging for the specific application — not an adapted generic blank — which allows for optimized strength-to-weight ratio and improved tensile strength over cast alternatives.

Kit Includes:

• 1 Forged aluminum piston
• 1 Piston ring set
• 1 Wrist pin
• 2 Wrist pin circlips

Key Specifications:

• MPN: 4971M09000
• Bore Size: 90.00mm (Standard Bore 89.92mm)
• Compression Ratio: 10.5:1
• Engine Displacement: 904cc
• Construction: Forged aluminum, USA-made

Wiseco's forged 4-stroke pistons are built to the tightest tolerances for the ultimate combination of performance and strength, and have been proven across decades of powersports and racing applications worldwide.