478M08750 Wiseco .020 Piston Kit for Yamaha YZ490 IT490 1982-1984 87.50 mm

Wiseco .020 Piston Kit for Yamaha YZ490 & IT490

This Wiseco .020 oversize piston kit for Yamaha YZ490 and IT490 models is an 87.50 mm piston assembly that restores compression and top-end power on worn cylinders, and the kit cross-references part numbers 478M08750.

Overview

This Wiseco .020 piston kit for Yamaha YZ490 and IT490 models is a direct-fit top-end rebuild component sized at 87.50 mm. The kit is intended for riders and mechanics refreshing a worn or scored cylinder on 1982 through 1984 machines. Each piston kit for Yamaha YZ490 and IT490 applications is manufactured to Wiseco specifications with part number 478M08750 stamped for identification.

Built For Performance

• .020 oversize bore size of 87.50 mm for cylinders that need cleanup honing
• Wiseco forged piston construction for strength under high-rpm loads
• Precision-machined ring grooves for consistent ring seal and compression
• Part number 478M08750 stamped for easy verification against the original
• Kit includes piston, rings, wrist pin, and circlips for a complete top-end refresh
• Sized specifically for Yamaha YZ490 and IT490 1982-1984 engines

Fits These Machines

• for Yamaha YZ490, 1982-1984
• for Yamaha IT490, 1982-1984

On-The-Job Use

• Top-end rebuilds on high-hour two-stroke dirt bikes
• Cylinder boring or honing to the next oversize after scoring
• Restoring compression on vintage motocross and enduro machines
• Routine piston replacement during engine refresh
• Rider or shop rebuilds where an oversize bore is required

Specs At A Glance

Good To Know

Q: Is this piston kit a genuine Yamaha part? A: No, it is a Wiseco-manufactured piston kit made for Yamaha YZ490 and IT490 fitment, not an OEM Yamaha part. The 478M08750 reference helps confirm it matches the original application.

Q: Do I need to bore the cylinder before installing this .020 piston? A: Because this is an oversize piston, the cylinder must be bored and honed to the matching 87.50 mm clearance before assembly. Checking ring end gap and piston clearance during installation is recommended.

Slight variation in finish or dimensions may occur between production runs, and fit can depend on serial number, so confirm compatibility before ordering.