Stihl MS 170 Air Filter (Cleaning & Care)
To clean the air filter on an STIHL MS 170, first identify the filter fitted to your saw and follow its manual’s cleaning instructions. Switch off and cool the engine, keep dirt out of the exposed intake, clean only by an approved method, and reinstall the filter fully dry and correctly seated. Replace it if damaged.
A clogged filter can restrict airflow and contribute to poor running, but cleaning it the wrong way can damage the filter or let grit reach the engine. The useful first step is not reaching for a brush or air hose. It is checking which filter is installed and what its instructions allow.
I treat filter care as two jobs: keep dust out of the intake while the filter is off, then make sure the filter seals properly when it goes back on. The MS 170 has a 30.1 cm³ engine, and it needs a clean, protected air path to run as designed. Filter versions and replacement parts can vary, so a method that suits one filter may not suit another.
Equipment identification and safety preparation
The filter type and its care instructions are the starting point. Check the owner’s manual for your saw’s model version and market, then compare the installed filter and its part number with the manual or an STIHL parts source. Do not choose a cleaning method by appearance alone.
Identify your filter before cleaning
Find the model information on the saw and use the applicable manual or parts diagram to confirm the filter. If the filter has been replaced, its part number may be more useful than the saw’s age. When you cannot confirm whether it is washable or dry-clean-only, pause and check with an authorized STIHL dealer rather than guessing.
A filter can look like a simple mesh or molded part, yet its material and construction determine how it should be cleaned. Some filters may allow washing; others require a specified dry-cleaning method. Do not assume that water, compressed air, or brushing is safe unless the instructions for that exact filter permit it.
Make the saw safe to service
Before opening the air-filter compartment:
- Switch off the engine, engage the chain brake, and let the saw cool.
- Work in a clean, ventilated area, away from dust and open flames.
- Wear eye protection and gloves.
- Brush or wipe dirt from around the cover before removing it.
- Keep the exposed intake protected from loose debris while the filter is out.
The last point matters. Dirt near the intake can fall inside during removal or cleaning. I take a moment to clear the area first, rather than trying to remove grit after it has entered the opening.
| Check | What to do | Why it matters |
|---|---|---|
| Saw is off and cool | Wait before opening the cover | Reduces burn and service risks |
| Area around cover | Remove loose dirt first | Helps keep debris out of the intake |
| Filter identity | Confirm type and part number | Cleaning rules vary by filter |
| Filter removed | Protect the open intake | Prevents debris entering the engine |
Next step: open the cover as described in the manual and lift the filter out carefully. Do not pry against the filter or push debris toward the intake.
Air-filter cleaning and reinstallation
Cleaning means removing dirt using only a method approved for the installed filter. The filter must then be fully dry, undamaged, and seated correctly before the saw is started. If you cannot verify those conditions, leave the saw off until you can inspect or replace the filter.
Inspect before cleaning
Look over the filter in good light. Check for:
- Tears, cracks, or holes in the filter material.
- Damaged edges or sealing surfaces.
- Packed dust that blocks the filtering area.
- Oil saturation or other contamination.
- A loose fit, distortion, or signs that the filter has not seated squarely.
A damaged filter is not made safe by washing or brushing it. Replace it with the correct part. A poor seal can let unfiltered air pass around the filter, even if the filter material itself looks clean.
Use the method specified for that filter
For a washable filter, use only the cleaner or mild soapy water allowed by its instructions. Rinse as directed, then leave it to dry completely. Do not reinstall it while damp.
For a filter specified for dry cleaning, follow its stated dry-cleaning method. Do not substitute water or another cleaner. In either case, avoid gasoline, harsh solvents, and high-pressure air or water unless the specific filter instructions expressly permit them. A strong blast can damage the filter or drive dirt through it.
While the filter dries, clean the housing with a clean, soft cloth or another method allowed by the manual. Work away from the intake opening. Do not push dust into the engine, and do not use cleaning fluid where it can run into the intake.
Reinstall and check the fit
Once the filter is fully dry, place it back in the correct position. Check that it sits squarely against its sealing surfaces, then refit the cover as directed by the manual. The cover should be secure, with no part of the filter pinched or displaced.
Do not run the saw with the filter or cover removed. Also stop if the filter is wet, torn, or does not fit correctly. Dust entering the engine can act as an abrasive and speed wear to internal parts.
| Filter condition | Recommended action |
|---|---|
| Dusty, intact, and type confirmed | Clean using that filter’s approved method |
| Washable type, still damp | Wait until completely dry |
| Torn or cracked | Replace; do not rely on cleaning |
| Oil-saturated or contaminated | Check the filter instructions; replace if they call for it or its condition is uncertain |
| Unknown type or part number | Confirm before cleaning |
| Does not seat securely | Stop and verify the correct filter and installation |
Next step: start the saw only after the filter and cover are installed securely. If it still runs poorly, stop and investigate other causes instead of altering settings to compensate.
Routine inspection helps you catch damage and poor seating before they become an intake-protection problem. Replace a filter that is damaged or cannot be cleaned as its instructions require. If the saw continues to run poorly with a clean, correct filter installed, the filter may not be the cause.
When to replace instead of clean
Replace the filter if it is torn, cracked, distorted, or unable to seal properly. Also replace it when its care instructions specify replacement, or when heavy contamination remains after the approved cleaning method. If you are unsure whether a filter is still serviceable, compare it with the manual’s guidance or ask a STIHL dealer.
Do not treat engine symptoms as proof that the air filter is dirty. A restricted filter can affect airflow, but poor running may also involve fuel, ignition, or carburetion. If cleaning and correct installation do not resolve the problem, stop and diagnose those systems using the manual or a qualified service technician.
The MS 170 is a two-stroke saw. STIHL’s published fuel mix is 50:1, but use the fuel specification and oil grade in the manual for your saw. That ratio is fuel guidance, not a filter-cleaning recipe. Published engine figures commonly list 2,800 rpm idle and 10,000 rpm maximum; verify them in the applicable manual. They are not targets for filter cleaning or a reason to adjust the carburetor after filter service.
Illustrative service situations
These examples show how I would make the decision at the bench; they are diagnostic scenarios, not reports of specific customer repairs.
- A dusty but intact filter: First identify its type. If its instructions allow cleaning, use only that method, let it dry fully if washing is permitted, then check that it seats squarely.
- A clean-looking filter that is torn at an edge: Replace it. The visible tear can allow dust past the filter, and cleaning cannot restore the damaged material or seal.
- A saw that still runs poorly after filter care: Confirm the correct filter is installed, dry, and seated, then stop and check for other causes. Do not keep cleaning an intact filter or change settings without a sound diagnosis.
Key takeaway: the filter’s condition and the quality of its seal matter as much as its visible cleanliness.
Storage and seasonal care
Storage care means putting the saw away with the filter clean enough for the next use, dry if its cleaning method involved washing, and correctly installed. Keep dust and moisture out of the filter compartment, and inspect the filter again before cutting after storage.
Before storing the saw, check whether the filter needs attention rather than cleaning it automatically. If it is dirty, follow its instructions; if it is clean and intact, leave it installed and close the cover. Keep the saw in a clean, dry storage area so dust does not settle into the air-filter housing.
After storage, inspect the cover and filter before starting. Look for a loose fit, visible damage, or debris around the housing. If you removed the filter for service, confirm it is fully dry and correctly seated before use. Never start the saw with the filter missing.
Next step: make the filter check part of your pre-use inspection, especially if the saw has been stored in a dusty shed or used in dry, gritty conditions.
Frequently asked questions
How do I clean the air filter on an MS 170?
Identify the installed filter, remove it as the manual directs, and clean it only by its approved method. Keep dirt out of the intake and reinstall the filter fully dry and correctly seated.
Can I wash every MS 170 air filter?
No. Filter types and instructions can vary. Confirm that the specific filter is washable before using water or cleaner.
Can I use compressed air to clean it?
Only if the instructions for that exact filter expressly allow it. High-pressure air can damage a filter or force dirt through it.
Can I use gasoline or solvent on the filter?
No, unless STIHL’s instructions for that specific filter expressly permit the product. Do not use gasoline or harsh solvents as a general cleaning method.
Can I start the saw without the air filter?
No. Keep the filter installed and the cover fitted before starting. An unprotected intake can admit abrasive dust into the engine.
Can I reinstall a damp filter?
No. If the filter’s approved cleaning method uses water, let it dry completely before reinstalling it.
When should I replace the filter?
Replace it if it is torn, cracked, distorted, will not seal, or cannot be cleaned as its instructions require. Use the correct replacement part.
What if the filter looks clean but the saw runs poorly?
Check that the filter is correct, dry, and seated. If the problem remains, stop and check other causes, such as fuel, ignition, or carburetion.
Where can I find the filter part number?
Check the applicable owner’s manual or parts diagram. If the filter was replaced before, compare its markings with the manual or ask an authorized STIHL dealer.
Does the 50:1 fuel mix affect air-filter cleaning?
No. The 50:1 ratio is fuel guidance for the applicable STIHL two-stroke specification. It is not a filter-cleaning mixture. Use the fuel and oil directions in your saw’s manual.
(This article was written by one of our staff writers, David Hensley. Visit our Meet the Team page.)
