STIHL MS 391 Petrol Chainsaw

High-torque chainsaw for agricultural and estate work

The STIHL MS 391 is a powerful 64.1 cm³ petrol chainsaw designed for heavy firewood processing, agricultural work, estate maintenance, horticulture and timber construction.

Its STIHL 2-MIX engine produces 3.3 kW / 4.5 hp and delivers strong torque across a wide operating range. This makes the MS 391 suitable for users who regularly process larger quantities of timber and need more output than the MS 291 provides.

Masseys offers the MS 391 with 16″ / 40 cm, 18″ / 45 cm and 20″ / 50 cm guide-bar options. Every version uses the same 64.1 cm³ powerhead; the difference is the fitted guide bar and matching saw chain.

Every petrol chainsaw sold by Masseys is assembled, inspected and test-run by our trained team before handover.

Browse our complete range of STIHL petrol chainsaws, read the Masseys STIHL chainsaw buying guide or use our STIHL chainsaw comparison chart.

Key features of the STIHL MS 391

• 64.1 cm³ STIHL 2-MIX petrol engine
• 3.3 kW / 4.5 hp power output
• 6.3 kg powerhead weight without fuel, guide bar or chain
• Choice of 16″, 18″ or 20″ guide bar
• 3/8″ STIHL Rapid Micro saw chain
• 1.6 mm drive-link gauge
• Manual decompression valve
• Side-mounted chain tensioning
• Variable-displacement chain-oil pump
• STIHL Ematic lubrication system
• Long-life air-filter system
• Carburettor compensator
• Tool-free fuel and chain-oil caps
• STIHL anti-vibration system
• Suitable for heavy agricultural, firewood and estate work

Who should choose the STIHL MS 391?

The MS 391 is intended for farmers, estate owners, smallholders, landscapers and experienced private users who regularly complete heavy cutting work.

It is particularly suitable for:

• Processing larger quantities of firewood
• Cross-cutting substantial hardwood and softwood logs
• Maintaining farms, estates and rural properties
• Clearing suitable storm-damaged timber
• Agricultural and horticultural work
• Timber construction
• Appropriately sized tree work by a competent operator
• Users who need more output than the MS 291 provides

The MS 391 is likely to be unnecessarily heavy for occasional garden pruning, small quantities of firewood or users who prioritise minimum weight and compact handling.

Choosing a 16-, 18- or 20-inch guide bar

All three configurations use the same 64.1 cm³ engine and 3.3 kW / 4.5 hp power output.

A longer guide bar provides additional reach, but it also increases front-end weight and leverage. It does not increase the engine’s power.

16″ / 40 cm guide bar

The 16-inch version provides the most compact and manoeuvrable MS 391 configuration.

Choose it when:

• You mainly process moderate-diameter firewood
• Ease of handling is important
• You often work around branches or confined areas
• You do not require the reach of a longer cutting attachment

18″ / 45 cm guide bar

The 18-inch model is STIHL’s current standard UK factory configuration and provides a balanced combination of cutting reach and handling.

Choose it when:

• You regularly process larger firewood and timber
• You want more reach than the 16-inch configuration
• You do not consistently need a full 20-inch cutting attachment

20″ / 50 cm guide bar

The 20-inch option provides the greatest reach of the three Masseys configurations.

Choose it when:

• You regularly encounter larger-diameter timber
• The full 50 cm bar length is genuinely required
• You are comfortable controlling the additional front-end weight and leverage

For many users, the 18-inch bar will offer the best compromise. Select the shortest bar that comfortably suits the timber you regularly cut.

64.1 cm³ STIHL 2-MIX engine

The MS 391 uses a 64.1 cm³ STIHL 2-MIX two-stroke engine producing 3.3 kW / 4.5 hp.

STIHL four-channel combustion technology directs the fuel-and-air mixture into the cylinder to support efficient combustion, high torque and consistent performance.

Compared with a previous equivalent STIHL engine without 2-MIX technology, STIHL states that fuel use can be reduced by up to 20% and emissions by up to 50%.

Manual decompression valve

A manual decompression valve reduces compression pressure within the cylinder during starting.

Pressing the valve before pulling the starter cord allows some compressed mixture to escape, reducing the force needed to turn the engine over.

The valve closes automatically when the engine fires.

3/8-inch Rapid Micro cutting system

The MS 391 uses a 3/8″ STIHL Rapid Micro chain with a 1.6 mm drive-link gauge.

The semi-chisel Rapid Micro profile provides:

• Strong all-round cutting performance
• Good edge durability
• Smooth cutting behaviour
• Low vibration
• Suitability for firewood, agricultural and estate work

The required chain length depends on the selected guide bar:

Guide bar	Pitch	Gauge	Drive links
16″ / 40 cm	3/8″	1.6 mm	60
18″ / 45 cm	3/8″	1.6 mm	66
20″ / 50 cm	3/8″	1.6 mm	72

Always check the markings on the fitted guide bar before ordering from our replacement chainsaw chain range.

Side-mounted chain tensioning

The chain-tensioning screw is positioned through the side of the sprocket cover.

This gives protected access to the adjustment point and avoids positioning the combination tool directly beside the sharp cutting teeth.

Check the chain tension:

• Before each use
• After fitting a new chain
• During extended cutting sessions
• Whenever the chain no longer sits correctly against the underside of the guide bar

Switch off the engine, allow hot components to cool and wear protective gloves before handling or adjusting the chain.

Variable-displacement chain-oil pump

The MS 391 allows chain-oil delivery to be adjusted according to the cutting attachment and timber conditions.

The economy position reduces unnecessary oil use during normal work. Additional oil delivery can be selected when using a longer guide bar or cutting very dry timber.

Check the oil level and lubrication before beginning work. Operating with inadequate oil can quickly damage the guide bar and chain.

STIHL Ematic lubrication system

The STIHL Ematic system combines the guide bar, Oilomatic chain and controlled-delivery oil pump to direct lubricant towards the areas where it is needed.

When the appropriate cutting attachment and oil are used, STIHL states that chain-oil consumption can be reduced by up to 50%.

Add suitable STIHL chainsaw chain oil before the first use.

Long-life air-filter system

The long-life filtration system separates larger dirt and sawdust particles from the cooling airflow before they reach the main filter.

This helps extend cleaning intervals and supports dependable engine performance during dusty agricultural and firewood work.

The filter must still be inspected, cleaned and replaced in accordance with the operating instructions.

Carburettor compensator

The carburettor compensator helps maintain engine output, fuel consumption and exhaust quality as the air filter gradually becomes contaminated.

This allows the chainsaw to continue working consistently for longer before a noticeable performance reduction indicates that filter maintenance is required.

STIHL anti-vibration system

Spring and buffer elements reduce the amount of engine and cutting vibration transmitted to the front and rear handles.

This can make the MS 391 more comfortable to control during appropriate extended work. It does not remove all vibration, so correct technique and regular breaks remain important.

Tool-free fuel and oil caps

The fuel and chain-oil tanks use bayonet-style caps that can be opened and closed without a separate tool.

Always ensure both caps are correctly aligned and fully locked before starting the engine.

Fuel and chain-oil requirements

The MS 391 requires two separate fluids:

• A 50:1 mixture of petrol and approved two-stroke engine oil for the engine
• Dedicated chain oil for the guide bar and saw chain

For self-mixed fuel, use suitable fresh petrol with approved STIHL two-stroke engine oil at the correct ratio.

STIHL MotoMix can also be used as a ready-mixed 50:1 fuel with a consistent formulation and longer storage life than ordinary self-mixed petrol.

The cutting attachment requires separate STIHL chain oil. Never place two-stroke engine oil in the chain-oil tank.

Fuel, two-stroke engine oil, chain oil and protective equipment are not included unless expressly listed as part of the offer.

STIHL MS 291 vs MS 391

Specification	STIHL MS 291	STIHL MS 391
Positioning	Agricultural and landowner chainsaw	Heavy agricultural and estate chainsaw
Displacement	55.5 cm³	64.1 cm³
Power output	2.8 kW / 3.8 hp	3.3 kW / 4.5 hp
Bare machine weight	5.6 kg	6.3 kg
Best suited to	Frequent firewood, farm and estate maintenance	Heavier timber and larger-volume agricultural work

Choose the STIHL MS 291 when lower weight and easier handling are more important than maximum output.

Choose the MS 391 when the additional engine capacity and 0.5 kW of power justify the extra machine weight.

MS 391 or a professional forestry chainsaw?

The MS 391 is positioned for agriculture, construction, horticulture, estates and demanding private use. It is not identical to a professional forestry saw designed for daily commercial harvesting.

Consider a professional forestry model when:

• The saw will be used commercially every day
• Professional power-to-weight performance is a priority
• Rapid acceleration and forestry-specific durability are required
• Electronic engine management is important

Compare suitable alternatives in the STIHL petrol chainsaw range or contact Masseys for advice.

Technical specifications

Specification	Details
Model	STIHL MS 391
Product type	Heavy agricultural and estate petrol chainsaw
Engine	STIHL 2-MIX two-stroke petrol engine
Displacement	64.1 cm³
Power output	3.3 kW / 4.5 hp
Machine weight	6.3 kg without fuel, guide bar or saw chain
Power-to-weight ratio	Approximately 1.9 kg/kW
Guide-bar options	40 cm / 16″, 45 cm / 18″ or 50 cm / 20″
Chain pitch	3/8″
Chain gauge	1.6 mm / .063″
Recommended chain type	STIHL Rapid Micro
16″ chain	60 drive links
18″ chain	66 drive links
20″ chain	72 drive links
Starting assistance	Manual decompression valve
Chain tensioning	Side mounted, adjusted with combination tool
Chain lubrication	Automatic STIHL Ematic system with adjustable oil pump
Air filtration	Long-life air-filter system
Fuel mixture	50:1 petrol and approved two-stroke engine oil, or STIHL MotoMix
Fuel and oil caps	Tool-free bayonet caps
Current 18″ factory MPN	11402000731

What is included?

The standard package should include:

• STIHL MS 391 petrol chainsaw
• Selected 16″, 18″ or 20″ guide bar
• Matching STIHL saw chain
• Guide-bar scabbard
• Combination tool
• Operating and safety instructions

Fuel, two-stroke engine oil, chain oil and personal protective equipment are not included unless specifically stated.

Maintenance and Service Kit 13

Routine maintenance helps protect engine performance, cutting efficiency and machine life.

Regular checks should include:

• Chain tension and sharpness
• Guide-bar condition
• Chain-oil delivery
• Air-filter condition
• Fuel filter
• Spark plug
• Chain-brake operation
• Starter mechanism

STIHL Service Kit 13 is designed for the MS 271, MS 291, MS 311 and MS 391 and includes routine air-filter, fuel-filter and spark-plug components.

Chainsaw safety and protective equipment

The MS 391 is a powerful petrol chainsaw and should only be operated by someone with appropriate instruction, protective equipment and an understanding of kickback and safe cutting techniques.

Before use:

• Read the operating and safety instructions
• Understand the chain brake and kickback risks
• Inspect the timber and surrounding work area
• Check chain tension and lubrication
• Keep bystanders and animals clear
• Plan a safe escape route for tree work

Suitable protective equipment should include:

• Chainsaw protective trousers
• Chainsaw boots or suitable cut-resistant footwear
• Eye or face protection
• Hearing protection
• Protective gloves
• A suitable helmet where falling material presents a risk

Browse our chainsaw protective trousers and wider range of chainsaw accessories and PPE.

Never operate a chainsaw from a ladder. Larger, leaning, damaged or difficult trees require appropriate professional competence, planning and equipment.

Warranty

STIHL’s standard warranty is two years for domestic use or one year for professional use, subject to current terms, correct application and appropriate maintenance.

Professional customers purchasing qualifying petrol machinery may be able to extend the warranty using an eligible STIHL Smart Connector promotion. Confirm current eligibility with Masseys at the point of purchase.

Why buy the STIHL MS 391 from Masseys?

Masseys is a STIHL Authorised Dealer based in Woodville, near Swadlincote.

Every petrol chainsaw sold by Masseys is assembled, inspected and test-run by our trained team before handover.

Buying from Masseys gives you access to:

• Help choosing between the 16-, 18- and 20-inch versions
• Advice comparing the MS 291, MS 391 and professional alternatives
• Genuine UK STIHL machinery and cutting attachments
• Product preparation and operating guidance
• Warranty registration and support
• Replacement guide bars and chains
• Fuel, two-stroke engine oil and chain oil
• Chain sharpening and workshop support
• Local collection and delivery options

Our garden machinery servicing and repairs workshop can assist with maintenance, repairs, genuine replacement parts and chain sharpening.

For help choosing the correct guide-bar length or confirming a product identifier, please contact Masseys before ordering.

Frequently asked questions

What engine does the STIHL MS 391 have?

It has a 64.1 cm³ STIHL 2-MIX petrol engine producing 3.3 kW / 4.5 hp.

How much does the MS 391 weigh?

The machine weighs approximately 6.3 kg without fuel, guide bar or saw chain. Its complete operating weight is higher after the selected cutting attachment, fuel and chain oil are added.

Is the MS 391 a professional chainsaw?

STIHL positions it primarily for heavy agricultural, construction, horticultural, estate and firewood work. It is not identical to a purpose-built professional forestry chainsaw intended for continuous commercial harvesting.

Should I choose the 16-, 18- or 20-inch version?

Choose the shortest guide bar that comfortably suits your normal timber. The 16-inch version offers the easiest handling, the 18-inch version provides a balanced compromise, and the 20-inch version supplies the greatest reach.

Is the 20-inch version more powerful?

No. All three configurations use the same 64.1 cm³, 3.3 kW powerhead. Only the guide bar and matching chain change.

Which chain does the MS 391 use?

It uses a 3/8″ STIHL Rapid Micro chain with a 1.6 mm gauge. The 16-inch bar uses 60 drive links, the 18-inch bar uses 66, and the 20-inch bar uses 72.

What is the difference between the MS 291 and MS 391?

The MS 391 has a 64.1 cm³, 3.3 kW engine compared with the MS 291’s 55.5 cm³, 2.8 kW engine. The MS 391 provides more output but is approximately 0.7 kg heavier before the cutting attachment and fuel are fitted.

Is the MS 391 better than the MS 291?

It is better suited to heavier cutting and larger-volume work. The MS 291 may be preferable where lower weight, easier handling and reduced purchase cost are more important.

What does the decompression valve do?

It reduces cylinder compression during starting, lowering the force required on the starter cord.

Can the chain-oil flow be adjusted?

Yes. The variable-displacement oil pump allows the lubrication level to be adjusted for different bar lengths and timber conditions.

What fuel does the MS 391 use?

It uses a 50:1 mixture of suitable petrol and approved two-stroke engine oil. STIHL MotoMix ready-mixed fuel can also be used.

Does it need separate chain oil?

Yes. Dedicated chainsaw chain oil must be added to the chain-oil tank to lubricate the guide bar and chain.

Does it include fuel or oil?

Fuel, two-stroke engine oil and chain oil are not normally included unless expressly stated as part of the offer.

Can the MS 391 cut hardwood?

Yes, provided the timber is appropriate for the selected bar and the chain is sharp, correctly tensioned and properly lubricated. Cutting performance depends on species, diameter, moisture and condition.

Can it fell trees?

It can be used for appropriately sized tree work by a competent operator. Larger, leaning, damaged or difficult trees require appropriate professional training, planning and equipment.

Which service kit fits the MS 391?

STIHL Service Kit 13 is designed for the MS 271, MS 291, MS 311 and MS 391.

Can Masseys service and sharpen it?

Yes. Masseys provides chainsaw servicing, repairs, replacement parts and chain sharpening through its on-site machinery workshop.