Boost your chain cutting velocity, step up limbing speed, and restore crisp drive engagement to your mid-range STIHL chainsaw with the Genuine OEM STIHL 0.325" 8-Tooth Spur Chain Sprocket Drum Assembly. Precision-manufactured under factory part number 1121 640 2005 (1121-640-2005), this heavy-duty, one-piece spur sprocket and clutch drum unit is an exact direct-fit upgrade designed to replace worn or grooved standard 7-tooth spur drums. Installing a fresh factory 8-tooth spur sprocket increases linear chain speed for faster cutting in clean wood while eliminating chain chatter and preventing drive link damage.
Featuring an 8-tooth (8T) drive spur profile calibrated specifically for .325" pitch guide bars and chains, this drive drum maximizes cutting efficiency on high-revving mid-displacement powerheads. Crafted as a single, solid-forged steel component, the integral drive teeth are induction-hardened to resist severe frictional wear, heat buildup, and chain slap. Its internal drum bore and oiler drive notch interface seamlessly with your saw's clutch shoes, needle bearing, and oil pump drive system (including 026 Pro models with spring-driven oiler gears) for immediate, trouble-free operation.
True Genuine OEM Manufacturing vs. Cheap Aftermarket Drums: Chainsaw drive drums spin at upwards of 13,000 RPM while taking the full mechanical force of your engine's clutch assembly. 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 running .325" pitch cutting setups. Direct replacement and speed-up upgrade 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.
- High-Speed 8-Tooth (8T) Drive Gearing: Increases linear chain velocity compared to standard 7-tooth drums, speeding up light bucking, pruning, and limbing tasks.
- Induction-Hardened Steel Spur Teeth: Precision-ground drive spurs resist premature grooving, keeping chain drive links meshing smoothly and safely under heavy loads.
- Integral One-Piece Drum Design: Combines the clutch drum and drive sprocket into a single rigid unit, offering simple, tool-free drop-in replacement 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 2005 (1121-640-2005 / 11216402005) |
| Chain Pitch Specification | .325" Pitch Exclusively |
| Tooth Count Profile | 8-Tooth (8T) Fixed High-Speed 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 | High-Speed Limbing, Firewood Processing, Storm Cleanup, and Professional Forestry |