STIHL Drive Pinion - 4243 640 2503

The STIHL Drive Pinion - 4243 640 2503 restores factory-spec rotational transfer between the crankshaft coupling and clutch assembly, maintaining precise timing under high-load cutting conditions.

Key Features

• Precision-gear cut hardened steel construction matched to original tooth profile and module
• Controlled backlash tolerance ensures stable engagement with the spur gear and drive sprocket
• Heat-treated contact surfaces resist scoring and pitting caused by prolonged friction cycles
• Exact dimensional replication eliminates trial-and-error fitting during routine maintenance swaps

Product Details

Serving as the primary power transmission component within the saw’s drivetrain, this pinion transfers rotational force from the engine crankshaft outward through the centrifugal clutch mechanism. The unit incorporates ground bearing journals and a standardized interface compatible with STIHL master rollers and clutch drums. Proper function depends on matching the designated gear ratio and pitch circle diameter to prevent accelerated wear on the drive sprocket or secondary chain components.

Compatibility

• Manufactured to replace OEM reference 4243 640 2503 across relevant STIHL production runs
• Fits platforms where factory service documentation specifies this drive pinion iteration
• Confirm mounting flange clearance, shaft diameter, and total tooth count prior to installation