Stihl MS 391 chainsaw flywheel crack projectile hazard (CPSC Feb 14, 2012)

## Affected machines About **3,000 US units** of Stihl **MS 391** gas-powered chainsaws. The MS 391 is a Farm Boss class saw — Stihl's higher-displacement homeowner / farm-and-ranch tier, slotting between the MS 311 and the professional MS 461. It's a popular saw with rural property owners and remained in the Stihl US lineup through 2022. ### Identifying an affected unit The chainsaws have an **orange top casing, gray base, black front handle, and black hand guard**. "STIHL" and "MS 391" are printed in an **orange circle on the starter side** of the unit. The serial number is on the **crankcase to the right of the muffler when viewed from the rear of the saw**. Recalled chainsaws have serial numbers in **five specific ranges**: - 285351759 through 285351956 - 286645278 through 286646277 - 286651283 through 286655577 - 287244317 through 287244480 - 287353627 through 287353647 ### Production / sales window Manufactured **February 2011 through June 2011** in the United States. Sold at **authorized Stihl dealers nationwide** from **March 2011 through July 2011** for **between $530 and $550**. ## Issue The **flywheel can crack**, causing parts of the flywheel to separate and strike the user or bystanders. The flywheel is a high-RPM rotating mass mounted on the engine crankshaft, used to smooth power delivery and (on a chainsaw) drive the magneto for ignition. Flywheels operate at engine speeds (~13,000 RPM on a saw under load) and are built for substantial centripetal stress; a flywheel failure at full RPM can eject metal fragments at high velocity through the saw housing. A cracked flywheel may **not be visible to a visual inspection** — the defect is in the casting or post-machining stress profile of the part. The remedy is **wholesale replacement** of the flywheel rather than inspection of the existing one. Reported field incidents at recall time: - 0 incidents reported - 0 injuries The recall was conducted as a **proactive safety action** by Stihl based on its own quality investigation rather than in response to field injuries. ## What to do 1. Find the **serial number on the crankcase** to the right of the muffler when viewed from the rear of the saw. 2. Check whether your serial number falls within any of the five ranges listed above. 3. If your saw is in scope, **stop using it immediately**. 4. Bring the unit to an **authorized Stihl servicing dealer** for free flywheel replacement. 5. Or call Stihl Inc. at **800-610-6677** Monday-Friday 8 a.m. - 8 p.m. ET, or email **stihlrecall@stihl.us**. 6. Online: https://www.stihlusa.com/information/recalls/recall-ms-391-powerhead ## Hazard Severity is rated **warning** because no incidents had been reported at recall time. The flywheel-projectile hazard is severe in principle but the field defect rate appears to have been low; Stihl's proactive recall closed the issue before manifest injuries occurred. ## Related bulletins - **TNB02600080** — Stihl MS 461 / MS 461 R chainsaw fuel-line pinch fire hazard (CPSC Feb 23, 2017). Different defect, same Stihl chainsaw family era. - **TNB02600082** — Stihl MS 361 C-Q chainsaw throttle trigger sticking laceration hazard (CPSC Dec 23, 2010). Different defect, same chainsaw family. - **TNB02600079** — Stihl MSA 300 battery chainsaw delayed-brake recall (CPSC 2023). ## Source - U.S. Consumer Product Safety Commission, "STIHL Recalls Chain Saws Due to Risk of Injury," February 14, 2012. - Manufacturer: Stihl Inc., of Virginia Beach, Virginia. - Stihl recall page: https://www.stihlusa.com/information/recalls/recall-ms-391-powerhead