Products Description
MS381 Chainsaw Oil Seal 17x40x5mm – Crankcase Seal Kit
Durable Crankshaft Seal Replacement for STIHL 038, MS380 & MS381
This 17x40x5mm oil seal is a direct replacement for the crankcase sealing system on STIHL MS381, MS380, and 038 series chainsaws. The oil seal is a critical component that prevents air leaks into the crankcase and stops the fuel/oil mixture from leaking out of the engine . A failing seal can cause hard starting, erratic idling, and loss of engine power. Available as an aftermarket replacement for OEM part number 9640 003 1880 , this seal ensures proper crankcase pressure for reliable two-stroke engine operation.
Technical Profiles & Materials
Precision Crankshaft Sealing – Designed to seal the crankshaft at the clutch side of the engine, preventing air leaks and maintaining proper crankcase pressure essential for correct two-stroke operation . Replacing worn seals restores engine performance.
Direct OEM Replacement Fitment – Replaces STIHL OEM part number 9640 003 1880 . Fits STIHL 038, MS380, and MS381 chainsaw models .
Aftermarket Quality Construction – Manufactured as a quality aftermarket replacement part from durable materials that resist oil degradation, engine heat, and vibration common in chainsaw operation .
Available as Complete Seal Kits – Some suppliers offer this oil seal as part of a set that includes both clutch and flywheel side seals, ensuring a comprehensive crankcase seal replacement during engine service .
Technical Specifications
| # | Parameter | Specification |
|---|---|---|
| 1 | OEM Part No. | 9640 003 1880 |
| 2 | Size (Actual) | 17mm ID × 39.6mm OD × 4mm thickness |
| 3 | Size (Reference) | 17x40x5mm (nominal specification) |
| 4 | Compatible Models | STIHL 038, MS380, MS381 |
| 5 | Also Fits | STIHL 028, 031, 032, BR420, SR400, SR420, FS360, FS420 (flywheel side) |
| 6 | Installation Position | Clutch side crankshaft |
| 7 | Cross Reference | 9640 003 1340 (flywheel side) |
| 8 | Material | Oil-resistant rubber with metal outer case |
Products Application
Crankcase Seal Replacement
Direct replacement when the original oil seal becomes hardened, cracked, or loses elasticity due to heat and engine stress. A worn seal can cause air leaks, leading to lean running conditions, poor idling, and hard starting .
Full Engine Overhaul Service
When performing a complete engine rebuild or top-end overhaul on the MS381, replacing both crankshaft oil seals is recommended. Available as a set with the flywheel side seal (9640 003 1340) to ensure all sealing components are renewed simultaneously .
Preventative Maintenance
Regular inspection and replacement of oil seals during routine chainsaw service helps maintain engine efficiency, prevents oil leaks, and extends engine life. As noted by experienced users, replacing worn seals can cure idling problems and resolve air leaks around the crankshaft .
Quality and Craftsmanship Details
Products Package
About Us
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FAQ
Q: How do I confirm this oil seal fits my MS381 chainsaw?
A:Check your chainsaw model number on the housing. This seal fits STIHL 038, MS380, and MS381 models . It replaces OEM part number 9640 003 1880 and is the clutch side oil seal . For the flywheel side, use 9640 003 1340 .
Q: What are the symptoms of a worn oil seal?
A: Common symptoms include hard starting, erratic or hunting idle, loss of engine power, and visible oil leaks around the crankshaft area . A failing seal allows air to enter the crankcase, causing a lean running condition that can lead to engine damage if not addressed promptly.
Q: What is the difference between the 17x40x5mm and the actual 17x39.6x4mm specification?
A: The 17x40x5mm is a nominal reference size commonly used for identification. Actual OEM-spec replacement seals measure 17mm inner diameter × 39.6mm outer diameter × 4mm thickness . Both references point to the same replacement part for the MS381 clutch side crankshaft seal.
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