STIHL® MS 391 Chainsaw

The STIHL MS 391 is a high-displacement farm and acreage chainsaw built for regular firewood cutting, rural property maintenance, storm cleanup, construction timber, and demanding work in medium to larger logs.

Its 64.1 cc STIHL 2-MIX engine produces 3.3 kW or approximately 4.5 hp, giving it more displacement than the MS 362 C-M and enough torque to support longer guide bars and sustained cutting. The powerhead weighs approximately 6.2 kg, placing the MS 391 firmly above the MS 291 and below STIHL’s larger professional felling saws in size and capability.

The MS 391 is not a professional forestry saw in the same sense as the MS 362 C-M or MS 400 C-M. Instead, it is designed for farmers, landscapers, tradespeople, acreage owners, and serious firewood cutters who want substantial engine capacity at a lower purchase price than a professional model.

Our Recommendation

We recommend the STIHL MS 391 to customers who regularly cut larger firewood, maintain wooded rural properties, or need a strong saw for farm and construction use without paying for professional power-to-weight.

It is especially well suited to customers who:

• Frequently use an 18-inch or 20-inch bar
• Cut several cords of firewood each year
• Work with larger softwood or moderate hardwood
• Need more capability than an MS 291
• Value displacement and torque more than minimum weight
• Want a durable farm-class saw with familiar mechanical controls

The MS 391 is not the best choice for every operator. At approximately 6.2 kg without the cutting attachment, it is heavier than the MS 362 C-M while producing slightly less rated power. Customers carrying a saw throughout the day or using it professionally will usually benefit from the lighter professional construction and M-Tronic management of the MS 362 C-M.

For farm, acreage, and firewood work where purchase value matters more than professional weight reduction, the MS 391 remains a practical and capable option.

Best Suited For

The STIHL MS 391 is particularly well suited to:

• Regular and higher-volume firewood cutting
• Farms, acreages, and rural properties
• Bucking medium and larger fallen trees
• Storm and windfall cleanup
• Cutting construction timber
• Fence-line and trail maintenance
• Landscaping and property-management work
• Experienced homeowners who have outgrown an MS 291
• Customers who want substantial displacement without stepping into a larger professional saw

64.1 cc Power for Larger Property Work

The MS 391 uses a 64.1 cc engine producing 3.3 kW or approximately 4.5 hp. STIHL positions it for firewood cutting, landscape maintenance, agriculture, and construction timber.

That additional displacement becomes useful when cutting:

• Larger firewood rounds
• Dense softwood
• Moderate hardwood
• Repeated logs during longer cutting sessions
• Storm-damaged trees
• Rural construction timber
• Material that places sustained demand on an 18-inch or 20-inch bar

The MS 391 is designed to provide dependable torque rather than the lighter, faster-revving feel of a professional saw. That makes it well suited to owners who want a substantial work saw but do not need to carry it through a full forestry shift.

Where the MS 391 Fits in the STIHL Lineup

The MS 391 sits above the MS 291 in STIHL’s farm and acreage range and below the larger professional models intended for high-production forestry.

Compared with the MS 291, it adds displacement, power, and greater comfort in larger wood.

Compared with the MS 362 C-M, it offers:

• More displacement
• A lower purchase price
• Conventional mechanical engine management
• A heavier farm-class chassis
• Slightly less rated power
• A lower professional power-to-weight ratio

The MS 391 is best understood as a large rural property and firewood saw, not as a budget version of the MS 362 C-M. The two models are built around different priorities.

What Can the STIHL MS 391 Cut?

The MS 391 is capable of handling a broad range of heavier property work, including:

• Processing annual firewood
• Bucking medium and larger fallen trees
• Cutting rural construction timber
• Removing storm-damaged limbs
• Clearing wooded fence lines
• Maintaining access roads and trails
• Felling manageable trees where the operator has the appropriate training
• Cutting logs that regularly exceed the comfortable workload of an MS 291

Guide-bar length should not be treated as the only measure of cutting capacity. Wood species, chain sharpness, cutting technique, engine condition, and the amount of continuous work all affect how comfortably the saw performs.

The MS 391 can reach through substantial timber, but operators facing very large trees or long-bar work as a primary application should consider the MS 462 C-M, MS 500i, MS 661 C-M, or larger models.

Choosing a Guide-Bar Length

The correct bar length should reflect the wood being cut most often, not simply the largest bar the saw can accept.

16-Inch Bar

A 16-inch bar creates the lightest and most responsive MS 391 configuration.

It is suitable when:

• Most wood is medium-sized
• Limbing and cleanup are common
• The saw will be carried around a large property
• Manoeuvrability matters more than reach
• The operator wants the engine to feel especially responsive

A short bar may seem unusual on a 64.1 cc saw, but it can produce excellent cutting performance in dense firewood.

18-Inch Bar

An 18-inch bar offers a strong balance of reach, handling, and engine load.

It is a good choice for:

• Mixed firewood sizes
• General farm and acreage work
• Storm cleanup
• Construction timber
• Customers who want one saw for varied rural work

For many owners, the 18-inch configuration will be the most versatile pairing.

20-Inch Bar

A 20-inch bar takes better advantage of the MS 391’s displacement and torque.

It is well suited to:

• Larger firewood rounds
• Bucking medium and larger logs
• Work where extra reach reduces repositioning
• Customers who regularly encounter timber beyond the comfort zone of an MS 291

The 20-inch bar adds front-end weight and requires the engine to drive more chain. Customers working primarily in smaller wood may find the 18-inch setup better balanced and faster to manoeuvre.

25-Inch Bar

A compatible 25-inch setup may be appropriate for occasional larger timber, but it should not automatically be selected simply because the saw can support it.

A longer bar:

• Adds weight
• Increases cutting resistance
• Requires careful chain maintenance
• Changes the saw’s balance
• Places greater demand on the oiling system
• May reduce cutting speed in smaller wood

Customers who regularly require a 25-inch bar may be better served by a professional model with a stronger power-to-weight ratio.

STIHL 2-MIX Engine

The MS 391 uses STIHL’s 2-MIX stratified-scavenging engine design.

During operation, a layer of fresh air separates burned exhaust gases from the incoming fuel mixture. STIHL uses this design to reduce fuel loss through the exhaust while maintaining strong engine performance.

The engine still requires gasoline mixed with the correct two-cycle oil. Straight gasoline must never be used.

Fuel quality is especially important for farm and acreage saws that may sit unused between cutting seasons. Old or contaminated fuel can contribute to:

• Hard starting
• Poor acceleration
• Unstable idle
• Carburetor deposits
• Reduced engine performance
• Fuel-system deterioration

For owners who use the saw intermittently, STIHL MotoMix can simplify fuel handling and long-term storage.

Long-Life Air-Filtration System

The MS 391 includes STIHL’s long-life air-filtration system.

Pre-separation removes larger dust and sawdust particles before they reach the primary filter. This helps slow filter contamination and extend the time between cleaning intervals. STIHL highlights the long-life filtration system as a core feature of the MS 391.

This is particularly valuable when cutting:

• Dry firewood
• Dead or weathered timber
• Dirty bark
• Windfall near the ground
• Construction timber
• Wood during dry Southern Alberta conditions

The filtration system still requires regular inspection. A heavily restricted, damaged, or incorrectly installed filter can reduce performance and allow abrasive material into the engine.

Compensator Carburetor System

The MS 391 uses STIHL’s compensator system to help maintain a consistent fuel-to-air ratio as the air filter gradually becomes contaminated.

This can help preserve engine performance and fuel economy between filter services. The compensator does not eliminate the need to inspect or clean the filter.

It also cannot correct:

• Stale fuel
• Incorrect fuel mixture
• A damaged air filter
• Blocked cooling passages
• A dull chain
• Mechanical wear
• Inadequate chain lubrication

The system extends useful operating intervals, but routine maintenance remains essential.

Side-Mounted Chain Tensioning

The MS 391 uses side-access chain tensioning.

The adjustment screw can be reached from the side of the powerhead using the combination wrench, reducing the need to work near the front of the guide bar. STIHL lists side-access tensioning among the saw’s standard convenience features.

Chain tension should be checked:

• Before every use
• After installing a new chain
• After the first few cuts
• Periodically as the chain warms
• After the chain cools
• Whenever the chain begins to sag beneath the bar

The engine must be shut off before adjustment, and gloves should be worn when handling the chain.

Tool-Free Fuel and Oil Caps

The MS 391 includes tool-free fuel and chain-oil caps with retainers.

These make refuelling and oil filling more convenient, but each cap must be properly seated and locked before the saw is started.

Before returning to work, confirm that:

• The cap is fully closed
• The sealing surface is clean
• No fuel has spilled onto the saw
• The cap is not damaged
• The saw has been moved away from the refuelling area

A damaged or incorrectly installed cap can leak fuel or bar oil.

STIHL Anti-Vibration System

The MS 391 uses an advanced anti-vibration system to reduce the amount of engine and cutting vibration transferred into the front and rear handles.

This can improve comfort during long firewood sessions and repetitive bucking work.

Reduced vibration does not eliminate fatigue. At over six kilograms before adding fuel, bar, chain, and oil, the MS 391 is still a substantial saw. Operators should take regular breaks and stop before fatigue begins to affect grip, balance, judgment, or reaction time.

STIHL Chainsaw Comparison

The MS 391 is the only farm and acreage model in this comparison. The remaining saws are professional models designed around stronger power-to-weight, higher production, and more frequent use.

STIHL MS 391 vs MS 362 C-M

The MS 391 and MS 362 C-M are close in displacement but substantially different in construction and operating experience.

The MS 391 has the larger engine, but the MS 362 C-M produces more rated power and weighs less.

We recommend the MS 391 when:

• Purchase value matters
• The saw is used seasonally rather than daily
• Firewood and rural property work are the main applications
• The customer prefers conventional engine management
• Additional weight is acceptable

We recommend the MS 362 C-M when:

• The saw will be carried or used throughout the day
• Professional power-to-weight matters
• Work takes place across changing temperatures and elevations
• Faster acceleration and reduced fatigue justify the additional cost
• M-Tronic engine management is valuable

The larger displacement of the MS 391 does not automatically make it the stronger-performing saw.

STIHL MS 391 vs MS 291

The MS 391 provides a substantial step up from the MS 291.

The MS 291 remains easier to handle and is sufficient for many acreage owners.

The MS 391 becomes worthwhile when larger wood, higher firewood volume, or longer cutting sessions regularly expose the limits of the MS 291.

Customers should not step up solely because the MS 391 is more powerful. The additional output comes with more weight, higher fuel consumption, and a less agile feel during limbing and smaller work.

STIHL MS 391 vs MS 400 C-M

The MS 400 C-M is the next major step in professional capability.

Although its displacement is only moderately greater, the MS 400 C-M is designed around professional power-to-weight, faster acceleration, electronic M-Tronic management, and sustained forestry use.

The MS 391 is the better choice when:

• The saw is used for seasonal firewood and property maintenance
• Purchase price matters
• The operator does not need professional daily durability
• Conventional controls are preferred
• The saw will not be carried for long forestry shifts

The MS 400 C-M is the better choice when:

• Production speed affects income
• The saw is used frequently or professionally
• Larger timber is encountered regularly
• Lower weight relative to output matters
• M-Tronic management is beneficial
• An 18-inch to 25-inch bar will be used heavily

The MS 400 C-M is not simply a slightly larger MS 391. It is a professional machine intended for a different level of workload.

What to Know Before Buying the MS 391

It is a heavy farm-class saw

The MS 391 weighs approximately 6.2 kg before the guide bar, chain, fuel, and bar oil are added. It will feel substantially heavier than an MS 291 or MS 261 C-M during limbing and extended carrying.

More displacement does not mean more power than the MS 362

The MS 391 has a larger engine than the MS 362 C-M, but the professional MS 362 produces slightly more rated power while weighing less.

It does not have M-Tronic

The MS 391 uses conventional engine management. It does not automatically compensate for changes in elevation, temperature, or operating conditions in the same way as an M-Tronic professional saw.

Long bars should match the workload

A 25-inch bar may be supported, but an 18-inch or 20-inch setup will usually feel faster and better balanced for common firewood and acreage work.

It requires mixed fuel

The engine operates on gasoline mixed with the correct two-cycle oil. Straight gasoline can cause rapid and severe engine damage.

It is not designed for occasional light cleanup

Customers cutting only small branches or occasional residential firewood will usually be better served by a lighter and less expensive model.

Fuel and Bar Oil

The MS 391 requires:

• Fresh gasoline mixed with suitable two-cycle oil
• Separate bar and chain oil for the cutting attachment

For seasonal users, STIHL MotoMix can simplify fuel storage and reduce problems associated with aging pump gasoline.

Customers mixing their own fuel should use suitable fresh gasoline and quality two-cycle oil at STIHL’s specified ratio.

The chain-oil level should be checked whenever the saw is refuelled. Running the saw without adequate lubrication can damage the:

• Guide bar
• Saw chain
• Drive sprocket
• Oil pump
• Clutch area

A longer guide bar may require closer attention to oil delivery and cleanliness of the bar-oil passages.

Chain Care and Sharpening

A sharp chain is essential to getting the expected performance from the MS 391.

Signs that the cutting system needs attention include:

• Fine sawdust instead of defined chips
• Slow cutting
• The saw pulling to one side
• Increased vibration
• Smoke despite adequate lubrication
• Heavy pressure required to complete the cut
• Uneven cutter length
• Blue discolouration on the guide bar

The chain pitch, gauge, and drive-link count must match the installed guide bar and sprocket.

Replacement chains, bars, files, bar oil, and related equipment can be found through the Arns STIHL chainsaw collection and chainsaw collection.

Maintenance and STIHL Service Kit 13

Routine maintenance for the MS 391 includes:

• Cleaning or replacing the air filter
• Inspecting the spark plug
• Replacing the fuel filter when required
• Cleaning cooling-air passages
• Checking the chain brake
• Cleaning the guide-bar groove and oil holes
• Rotating and dressing the guide bar
• Inspecting the drive sprocket
• Checking the recoil starter
• Examining the fuel and oil systems for leaks
• Sharpening and tensioning the chain

The STIHL Service Kit 13 is compatible with the MS 271, MS 291, MS 311, and MS 391. It contains common maintenance components for helping protect the engine from dirt and supporting reliable performance.

Maintenance intervals should be shortened when the saw is used heavily or operated in dusty conditions.

Seasonal Storage

Before storing the MS 391 for an extended period:

• Clean sawdust from the powerhead and sprocket cover
• Clean the guide-bar groove and oil holes
• Inspect and sharpen the chain
• Follow STIHL’s fuel-storage procedure
• Inspect the air filter
• Check for fuel and bar-oil leaks
• Fit the guide-bar cover
• Store the saw in a dry, secure location
• Keep it away from children and ignition sources

A large farm saw stored with stale fuel, a dirty filter, or a dull chain is far more likely to create starting and performance problems when it is needed again.

Chainsaw Safety

The MS 391 is a powerful saw intended for experienced users performing serious property work.

Operators should understand:

• Safe ground-starting procedures
• Chain-brake operation
• Kickback zones
• Proper limbing and bucking technique
• Compression and tension in fallen wood
• Escape routes during felling
• Hazards associated with leaning, split, damaged, or hung-up trees
• The additional balance changes created by longer guide bars

Recommended protective equipment includes:

• Chainsaw protective pants or chaps
• Eye protection
• Hearing protection
• Protective gloves
• Chainsaw-appropriate footwear
• A forestry helmet when overhead hazards are present
• High-visibility clothing where appropriate

Felling near homes, roads, utilities, fences, or neighbouring properties should be left to a qualified professional when the operator lacks the required training and equipment.

Why Buy Your STIHL MS 391 From Arns?

Arns Equipment is a family-owned STIHL dealer serving Calgary, Southern Alberta, and customers across Canada. Our team brings more than 80 years of outdoor power equipment experience to every chainsaw recommendation.

When you purchase the STIHL MS 391 from Arns, our team can help you:

• Choose the right guide-bar length
• Compare the MS 391 with the MS 291 and MS 362 C-M
• Decide whether a professional MS 400 C-M better suits your workload
• Select compatible chains, files, fuel, bar oil, and protective equipment
• Understand chain tension and routine maintenance
• Find replacement bars, chains, and accessories
• Source repair and maintenance parts through PartsHouse.ca
• Arrange local STIHL warranty support and professional service
• Avoid buying a heavier saw than the work requires

For farmers, acreage owners, landscapers, tradespeople, and serious firewood cutters who need more capability than the MS 291 but do not require a professional forestry chassis, the STIHL MS 391 offers substantial displacement, strong cutting torque, proven serviceability, and dependable support for demanding rural work.