Piston set with 3-5/8 inch bore 8.5:1 compression ratio and is oversize .010. Set includes Hastings 3 piece ring set 2 wrist pins and 4 circlips. pistons have a steel expansion control strut cast.
The Motorshop E-840-010 piston set is designed for Harley-Davidson engines using 4-1/2-inch stroke flywheels and 3-5/8-inch cylinders. This .010-inch oversize piston set is intended for applications requiring a finished bore size of 3.8750 inches. It is a suitable replacement component for restoring or rebuilding select Panhead and Shovelhead engines while maintaining proper cylinder and piston fitment.
Before installation, verify cylinder condition, bore specifications, piston clearance, and compatibility with the engine assembly. The finished bore must be accurately prepared to 3.8750 inches to fit 3-5/8-inch cylinders. Proper machine-shop measurement and piston fitting are essential for reliable operation. For installation and fitment guidance, refer to the manufacturer's instructions at Piston Fitment Instructions.
After installation, run the engine at moderate speeds for at least 500 miles to properly break in the new pistons and rings. Avoid excessive operation in lower gears during the break-in period, as proper loading and controlled engine speeds help support reliable ring seating and long-term performance. The Motorshop E-840-010 is supplied as a piston set kit and is compatible with listed 1948–1957 Harley-Davidson FL applications when matched to the correct engine specifications.
Features:
Application: Designed for engines with 4-1/2-inch stroke flywheels
Bore Fitment: Requires a finished bore size of 3.8750 inches for 3-5/8-inch cylinders
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