STIHL MS 661 C-M Professional Petrol Chainsaw

Description

The STIHL MS 661 C-M is a large-capacity professional petrol chainsaw developed for hardwood forestry, large-timber harvesting, production felling and demanding cross-cutting work.

Its 91.1 cm³ STIHL 2-MIX engine produces 5.4 kW / 7.3 hp from a powerhead weighing approximately 7.5 kg without fuel, guide bar or saw chain.

STIHL M-Tronic electronic engine management automatically regulates ignition timing and fuel metering, helping the saw maintain consistent starting, acceleration and engine performance as temperature, altitude, fuel quality and operating conditions change.

Masseys offers the MS 661 C-M with either a factory 28″ / 71 cm Rollomatic ES Light cutting attachment or a professional 36″ / 90 cm long-bar package.

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

Browse Masseys’ complete range of STIHL petrol chainsaws or read our STIHL chainsaw buying guide.

Important configuration information

The current STIHL UK factory configuration is supplied with a 28″ / 71 cm guide bar.

Masseys’ 36″ / 90 cm option is a long-bar package using a compatible professional STIHL guide bar and matching saw chain. Unless a separate complete-machine MPN is shown on the product packaging or STIHL dealer system, this should be treated as a Masseys-configured package rather than a separate factory machine.

Both options use the same 91.1 cm³ MS 661 C-M powerhead. The longer guide bar provides additional reach but does not increase engine output.

Key features of the STIHL MS 661 C-M

• Professional large-timber forestry chainsaw
• 91.1 cm³ STIHL 2-MIX petrol engine
• 5.4 kW / 7.3 hp power output
• 7.5 kg powerhead weight without fuel, guide bar or chain
• STIHL M-Tronic electronic engine management
• Choice of 28″ or 36″ professional cutting attachment
• 3/8″ STIHL Rapid Super full-chisel chain
• 1.6 mm drive-link gauge
• Side-mounted chain tensioning
• Variable-displacement chain-oil pump
• STIHL Ematic lubrication system
• Long-life filtration with HD2 filter
• Carburettor compensator
• Manual decompression valve
• Combi lever with stop function
• Captive sprocket-cover nuts
• Tool-free fuel and chain-oil caps
• STIHL anti-vibration system
• Designed for sustained professional forestry work

Who should choose the STIHL MS 661 C-M?

The MS 661 C-M is intended for trained professional users who regularly work with large-diameter timber and require substantially more capacity than a general forestry or landowner chainsaw provides.

Typical applications include:

• Professional hardwood forestry
• Felling large-diameter trees
• Cross-cutting substantial stems
• High-volume timber processing
• Large-scale storm-clearance operations
• Professional logging and harvesting
• Specialist long-bar cutting
• STIHL TIMBERSPORTS Stock Saw competition use in standard specification

The MS 661 C-M is not an appropriate general-purpose saw for occasional firewood, garden maintenance or inexperienced users.

For lighter mixed professional work, compare the STIHL MS 400.1 C-M, STIHL MS 462 C-M or STIHL MS 500i.

Choosing a 28-inch or 36-inch guide bar

Both configurations use the same engine and powerhead. The guide-bar choice affects reach, balance, working weight and the required saw-chain length.

28″ / 71 cm Rollomatic ES Light

The 28-inch version is STIHL’s current UK factory configuration and is the more manoeuvrable of the two Masseys options.

Choose it when:

• A 71 cm guide bar provides sufficient reach
• Lower cutting-attachment weight is important
• The saw will be used for mixed large-timber felling and cross-cutting
• You want the best balance for regular professional use

The Rollomatic ES Light bar is designed to reduce weight while retaining the stability required for demanding professional forestry work.

36″ / 90 cm long-bar package

The 36-inch package provides maximum reach for particularly large-diameter timber.

Choose it only when:

• A 28-inch bar is regularly insufficient
• The operator is trained and experienced with long guide bars
• The additional working weight and leverage can be safely controlled
• The workload genuinely involves very large timber

A 36-inch bar significantly increases the machine’s complete working weight and front-end leverage. The 28-inch configuration will normally be easier to manoeuvre where its cutting capacity is sufficient.

91.1 cm³ STIHL 2-MIX engine

The MS 661 C-M uses a 91.1 cm³ STIHL 2-MIX two-stroke petrol engine producing 5.4 kW / 7.3 hp.

The engine is designed to provide the sustained output required for long guide bars, large timber and continuous professional forestry workloads.

STIHL 2-MIX technology uses a stratified scavenging process to support strong output while reducing fuel consumption and exhaust emissions compared with older equivalent STIHL two-stroke engine designs.

STIHL M-Tronic engine management

STIHL M-Tronic is a fully electronic engine-management system.

It automatically regulates:

• Ignition timing
• Fuel metering
• Starting settings
• Fuel supply across the engine-speed range

The system accounts for:

• Engine and ambient temperature
• Altitude
• Fuel quality
• Air-filter condition
• Changing cutting loads

M-Tronic removes the need for normal manual carburettor adjustment and stores recent operating settings so they can be reapplied when the saw is restarted under similar conditions.

Reset and calibration procedures vary by M-Tronic generation. Follow the operating manual or consult Masseys’ workshop rather than using a generic reset procedure.

Simplified starting

The M-Tronic starting system uses one cold-start position rather than separate full- and half-choke settings.

The combi lever automatically returns to the normal operating position after the engine is stopped, simplifying warm restarting.

A manual decompression valve allows some cylinder pressure to escape during starting, reducing the force required on the starter cord.

3/8-inch Rapid Super cutting system

The MS 661 C-M uses a professional STIHL 3/8″ Rapid Super full-chisel chain with a 1.6 mm drive-link gauge.

Rapid Super is designed for:

• High professional cutting performance
• Felling and cross-cutting large timber
• Fast cutting in clean wood
• Low vibration for a full-chisel professional chain

Always confirm the guide-bar markings, pitch, gauge and drive-link count before ordering from Masseys’ replacement chainsaw chain range.

Side-mounted chain tensioning

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

This provides protected access to the adjustment mechanism without positioning the combination tool directly beside the chain’s cutting teeth.

Check 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

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

Variable-displacement chain-oil pump

The adjustable oil pump allows lubrication to be matched to the guide-bar length, timber and operating conditions.

The economy setting reduces unnecessary oil use during suitable cutting work. Additional oil delivery can be selected when using a very long guide bar or cutting particularly dry timber.

This adjustment is especially important when the 36-inch cutting attachment is fitted.

STIHL Ematic lubrication

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

Check the oil level and oil delivery before beginning work. Operating a long guide bar with inadequate lubrication can rapidly damage the guide bar, chain and drive system.

Add suitable professional STIHL chain oil before use.

HD2 filtration system

The HD2 filter protects the engine from fine forestry dust and debris.

Its PET filter material has fine pores and is oil- and water-repellent, helping protect the engine and supporting longer service intervals in demanding conditions.

The filter can be removed without tools but must still be inspected, cleaned and replaced in accordance with the operating manual.

Carburettor compensator

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

This allows longer operating intervals before filter contamination causes a noticeable reduction in performance.

Captive sprocket-cover nuts

The sprocket-cover nuts remain attached to the cover when loosened.

This reduces the risk of dropping or losing the nuts during guide-bar removal, chain changes and cleaning at the work site.

STIHL anti-vibration system

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

This supports greater comfort during appropriate professional use. It does not remove vibration, so correct technique, maintenance and exposure management remain essential.

Fuel and chain-oil requirements

The MS 661 C-M requires two separate fluids:

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

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

Compatible ready-mixed alkylate fuel can also be used where appropriate.

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 stated in the selected offer.

MS 400.1 C-M vs MS 500i vs MS 661 C-M

Choose the STIHL MS 400.1 C-M when lower weight and manoeuvrability are the priority.

Choose the STIHL MS 500i when rapid acceleration, fuel injection and a high power-to-weight ratio are more important than maximum long-bar capacity.

Choose the MS 661 C-M when the workload regularly involves very large timber and requires its additional displacement, output and compatible long cutting attachments.

Technical specifications

What is included?

The standard package should include:

• STIHL MS 661 C-M professional petrol chainsaw
• Selected 28″ or 36″ professional guide bar
• Matching STIHL Rapid Super saw chain
• Guide-bar scabbard
• Combination tool
• Operating and safety instructions

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

Maintenance and Service Kit 16

Regular professional maintenance helps protect M-Tronic performance, engine life and cutting efficiency.

Routine checks should include:

• Chain tension and sharpening
• Guide-bar condition
• Chain-oil delivery
• HD2 air-filter condition
• Fuel filter
• Spark plug
• Chain-brake operation
• Starter mechanism
• Cooling-air passages
• M-Tronic performance and calibration

STIHL Service Kit 16 contains the HD2 air filter, spark plug and fuel filter used for standard MS 661 maintenance. Browse Masseys’ STIHL service-kit range.

Professional safety and protective equipment

The MS 661 C-M is a high-output professional forestry chainsaw. It should only be operated by someone with appropriate training, experience and protective equipment.

Suitable protective equipment should include:

• Professional chainsaw trousers
• Appropriate chainsaw boots
• Forestry helmet
• Eye or face protection
• Hearing protection
• Protective gloves

Browse Masseys’ chainsaw trousers, chainsaw boots and wider range of professional forestry and chainsaw accessories.

Large, leaning, damaged or storm-affected trees require suitable professional planning, competence, equipment and exclusion zones.

Warranty

STIHL’s standard warranty for professional petrol tools is one year, subject to current terms, correct use and maintenance.

Qualifying professional users may extend the warranty from one to two years when the saw is purchased with an eligible STIHL Smart Connector and the extension is registered by the STIHL Approved Dealer at the point of sale.

Why buy the STIHL MS 661 C-M from Masseys?

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

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

Buying from Masseys gives you access to:

• Help choosing between the 28-inch and 36-inch packages
• Advice comparing the MS 400.1, MS 462, MS 500i and MS 661
• Genuine UK STIHL machinery and cutting attachments
• Product preparation and operating guidance
• Warranty registration and support
• Replacement professional guide bars and saw chains
• Fuel, two-stroke engine oil and chain oil
• M-Tronic diagnosis and workshop support
• Chain sharpening and genuine replacement components
• Local collection and delivery options

Our garden machinery servicing and repairs workshop can assist with servicing, M-Tronic diagnosis, repairs, replacement parts and chain sharpening.

For advice about guide-bar length, product identifiers or whether the MS 661 is appropriate for your work, please contact Masseys before ordering.

Frequently asked questions

Is the STIHL MS 661 C-M a professional chainsaw?

Yes. It is a professional large-timber forestry chainsaw designed for hardwood harvesting, high-output felling and demanding cutting work.

What engine does the MS 661 C-M have?

It has a 91.1 cm³ STIHL 2-MIX petrol engine producing 5.4 kW / 7.3 hp.

How much does the MS 661 C-M weigh?

The powerhead weighs approximately 7.5 kg without fuel, guide bar or saw chain. The complete working weight is substantially higher after the selected cutting attachment and fluids are added.

Why does Masseys offer 28-inch and 36-inch versions?

The 28-inch version is the current UK factory configuration. Masseys also offers a compatible 36-inch long-bar package for trained professional users who regularly work with very large timber.

Is the 36-inch version more powerful?

No. Both packages use the same 91.1 cm³, 5.4 kW powerhead. Only the guide bar and matching saw chain change.

Which chain does the 28-inch MS 661 use?

It uses a 3/8″ STIHL Rapid Super chain with a 1.6 mm gauge and 91 drive links.

Which chain does the 36-inch MS 661 use?

It uses a 3/8″ STIHL Rapid Super chain with a 1.6 mm gauge and 114 drive links.

What does M-Tronic do?

M-Tronic automatically controls ignition timing and fuel metering, adapting engine operation to factors including temperature, altitude, fuel quality and engine load.

Does M-Tronic require manual carburettor adjustment?

Normal manual carburettor tuning is not required. Dealer diagnosis or recalibration may occasionally be necessary following servicing or changes in performance.

Is the MS 661 better than the MS 500i?

The MS 661 provides greater displacement, slightly more power and compatibility with very long guide bars. The MS 500i is lighter and uses electronically controlled fuel injection for rapid acceleration. The better choice depends on timber size, bar requirements and daily workload.

Is the MS 661 suitable for ordinary firewood?

It is unnecessarily large and heavy for most ordinary domestic firewood work. A smaller professional or landowner saw will usually be easier and less tiring to operate.

What fuel does it use?

It uses a 50:1 mixture of suitable petrol and approved two-stroke engine oil. Compatible premixed alkylate fuel can also be used.

Does it require separate chain oil?

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

Can the chain-oil flow be adjusted?

Yes. The variable-displacement oil pump allows lubrication to be increased for long guide bars or particularly dry timber.

Which service kit fits the MS 661?

STIHL Service Kit 16 contains the HD2 air filter, spark plug and fuel filter used for routine MS 661 maintenance.

Can Masseys service an MS 661 C-M?

Yes. Masseys’ workshop can assist with servicing, M-Tronic diagnosis, repairs, replacement cutting attachments and chain sharpening.