Restore crisp drive engagement, smooth power transfer, and original factory cutting performance to your mid-range STIHL chainsaw with the Genuine OEM STIHL 0.325" 7-Tooth Spur Chain Sprocket Drum Assembly. Precision-engineered under factory part number 1121 640 2004 (1121-640-2004), this heavy-duty, one-piece spur sprocket and clutch drum unit is an exact direct-fit replacement designed to replace grooved, worn, or heat-damaged drive sprockets. Installing a fresh factory spur sprocket eliminates erratic chain chatter, prevents costly drive link burring, and stops chain slippage under heavy loads.
Featuring a 7-tooth (7T) drive spur profile calibrated specifically for .325" pitch guide bars and chains, this drive assembly delivers the optimal balance of cutting torque and engine RPM control for mid-displacement powerheads. Crafted as a single, solid-forged steel component, the integral drive teeth are induction-hardened to resist severe frictional wear caused by wood chips and bar oil sludge. Its internal drum bore and oiler drive notch interface seamlessly with your saw's clutch shoes, needle bearing, and oil pump drive wire for immediate, trouble-free operation.
True Genuine OEM Manufacturing vs. Cheap Aftermarket Drums: Chainsaw drive drums spin at over 13,000 RPM while taking the full mechanical load of your engine's clutch. Low-cost aftermarket spur drums frequently suffer from off-center machining, soft metal spur teeth that groove after just a few tanks of fuel, and out-of-spec drum walls that cause clutch slippage or severe engine vibration. Genuine STIHL drive components guarantee exact dynamic balance, precise needle bearing fitment, and commercial-grade durability.
Configuration & Fitment Profile: Factory-designed for small-to-mid chassis STIHL powerheads configured for .325" pitch cutting setups. Direct replacement for the clutch drive and oil pump systems across the legendary 026, 026 Pro, MS 260, MS 260 Pro, as well as the MS 270, MS 270 C-B, and MS 280 series. Needle bearing sold separately.
Key Features & Benefits
- 100% Genuine OEM STIHL Manufacture: Built to exact factory specifications using high-density, heat-treated structural steel alloys to guarantee proper fitment and long service life.
- Optimal 7-Tooth (7T) Torque Profile: Maintains ideal gearing for mid-displacement engines, delivering strong wood-biting torque during bucking and felling operations.
- Induction-Hardened Steel Spur Teeth: Precision-ground drive spurs resist premature grooving, keeping chain drive links meshing smoothly and safely.
- Integral One-Piece Drum Design: Combines the clutch drum and drive sprocket into a single rigid unit, offering simple, tool-free drop-in installation during routine servicing.
- Seamless Oil Pump Interface: Features precision drive notch geometry that engages smoothly with the oiler drive wire on adjustable and automatic oil pump models.
Technical Specifications & Master Fitment Chart
| Brand / Component Tier | STIHL® Genuine OEM Chainsaw Drive Line Component |
| Factory Part Number / SKU | 1121 640 2004 (1121-640-2004 / 11216402004) |
| Chain Pitch Specification | .325" Pitch Exclusively |
| Tooth Count Profile | 7-Tooth (7T) Fixed Spur Sprocket |
| Structure Type | One-Piece Clutch Drum with Integrated Fixed Drive Spur |
| Verified Compatible Models | • STIHL 026 / 026 Pro • STIHL MS 260 / MS 260 Pro • STIHL MS 270 / MS 270 C-B • STIHL MS 280 |
| Primary Application | Firewood Cutting, Property Maintenance, Storm Cleanup, and Forestry |