Stihl 325" 7 Tooth Spur Sprocket Kit - MS251, MS241C-M

Restore rigid, positive power delivery and original factory torque to your mid-range chainsaw with the genuine OEM STIHL .325" 7-Tooth Spur Sprocket Assembly. Precision-manufactured under factory part number 1143 640 2002, this structural clutch drum shell is an exact drop-in replacement component engineered for modern 1143-series engines, including the MS 231, MS 251, and professional M-Tronic MS 241 C-M powerheads. Swapping out a grooved or worn drive drum remedies erratic clutch slipping, stops immediate chain stall under load, and optimizes cutting throughput.

The core advantage of this original equipment manufacturer layout lies in its simple, rugged single-piece architecture. The 7-tooth spur configuration is precision-machined directly onto the exterior of the case-hardened alloy drum shell, ensuring perfectly rigid structural integrity and direct mechanical link-to-clutch contact. This standard factory setup provides excellent balanced engine leverage, preventing the engine from bogging down in demanding hardwoods while stabilizing linear chain delivery throughout the cut profile.

True OEM Engineering vs. Soft Aftermarket Metal: Chainsaw drive sprockets function under extreme frictional heat and high centrifugal stress. Low-grade aftermarket drums frequently suffer from out-of-round concentricity, causing catastrophic crankshaft vibration, rapid wear on internal clutch shoes, and premature failure of the integrated oiler notch. This genuine STIHL spur sprocket features a precision 13mm central bore to guarantee exact alignment with your needle cage bearing, ensuring a long operational life cycle and fluid oil pump engagement.

Configuration & Application Profile: Designed exclusively for STIHL 1143-series powerheads configured with a .325" pitch guide bar and chain loop assembly. This drum will not accept 3/8" Standard or 3/8" Picco (Low Profile) chain configurations. Packaged as a single, fully integrated spur sprocket and clutch drum shell unit without the needle bearing.

Key Features & Benefits

• Direct Single-Piece Architecture: Features a fixed 7-tooth spur gear machined directly to the drum, eliminating secondary loose components or floating wear pieces.
• Factory-Standard Balanced Torque: Maintains original engine-to-chain gear ratios to ensure peak mechanical leverage when bucking firewood or felling small timber.
• 100% Genuine OEM STIHL Manufacture: Built from premium, heat-treated high-carbon steel alloy designed specifically to withstand harsh commercial environments.
• Precision Oiler Notch Integration: Explicitly notched to interface seamlessly with the internal oil pump drive gear for continuous, high-RPM bar lubrication.
• Concentric Anti-Vibration Design: Precision-ground 66.5mm inner diameter tolerances minimize radial runout, protecting your engine's crankshaft and main bearings from stress.
• Full Variant Fitment Support: Perfectly compatible with standard engine configurations as well as specialized ErgoStart and Quick Chain Adjusting (C-BE) models.

Technical Specifications & System Components