Stihl MS 661 C-M vs. C-M R (Model Comparison)

The MS 661 C-M and MS 661 C-M R share the same 91.1 cm³ M-Tronic engine and published output of 5.4 kW (7.2 bhp). The key difference is that the C-M R adds electrically heated handles where that version is sold. Choose it for cold-weather work if your regional model includes the feature; otherwise, the C-M delivers the same engine class without handle heating.

Would you rather pay for a feature that helps on cold workdays, or keep the saw simpler because you rarely work in those conditions? That is the central choice between these two versions. Their names can make the difference look bigger than it is, so I’ll separate the shared engine and cutting setup from the feature that changes the buying decision.

When comparing listings, check the model plate and the specification for your market. Suffixes and equipment can vary by region. A listing title alone may not confirm which version you are buying.

The actual difference between the MS 661 C-M and C-M R

The C-M and C-M R are both professional saws with STIHL M-Tronic engine management. The R version adds electrically heated handles in markets where it is offered. That feature changes comfort in cold conditions, not the saw’s engine class or its basic cutting purpose.

Both versions are listed at 91.1 cm³ displacement and 5.4 kW (7.2 bhp) in the referenced specifications. Confirm those figures against the manual and model plate for the exact saw, since regional specifications may differ.

M-Tronic manages engine operation electronically. It is not a reason to expect different power from the R version, and it is not a license to adjust the saw like a conventional carburetor. Do not turn conventional high- or low-speed mixture screws; follow STIHL’s model-specific service instructions.

*Verify figures and equipment for the regional model.

In my review work, the most common comparison mistake is treating the “R” as a higher-power engine. The useful question is narrower: will heated handles matter during your actual work season? If not, the R feature may add little value to your decision.

Which version fits your work?

Both are large, high-power professional saws for demanding felling and bucking by trained operators. They can suit large-diameter hardwood, but no single bar length or engine size makes a saw right for every tree. Your cutting plan, the tree, the site, and your skill all matter.

Choose the C-M R if you work often in cold conditions and the exact regional version confirms heated handles. Cold hands can make handling less comfortable, but handle heating does not replace gloves, training, safe technique, or other protective equipment.

Choose the C-M if handle heating is not a priority or the R version is unavailable in your market. You are not stepping down to a different engine class based on the stated specifications above. Compare the actual equipment, condition, warranty, and local price rather than assuming the suffix signals more cutting power.

Before purchase, ask the dealer to confirm:

• The exact model shown on the saw’s plate
• Whether the handles are electrically heated on that unit
• Which bar and chain are supplied
• Whether the bar and chain are approved for that model
• Which manual and regional specifications apply

Bar, chain, and wood: choose the setup, not just the engine

A bar is the guide that supports the chain. Its length should match the tree diameter, cut plan, and operator’s ability, not just the saw’s displacement. STIHL lists bar options broadly around 50–90 cm (20–36 in.), depending on market. Use only combinations approved for the exact saw.

A common MS 661 setup uses a 3/8-inch chain pitch and .063-inch (1.6 mm) gauge. Pitch describes the chain’s link spacing; gauge is the thickness of the drive links that sit in the bar groove. Check the bar stamp and chain part number before fitting parts. Drive-link count varies by bar model and length.

There is no universal hardwood rating that tells you which bar to use. Wood species and size matter, but so do lean, defects, access, footing, and the sequence of cuts. A longer bar is not automatically safer or more effective. Follow the manual and get qualified felling guidance when the tree or site is beyond your training.

Equipment setup and safety preparation

Setup means checking the saw, fitting a matched cutting system, and preparing the site before starting. The same core preparation applies to either version. Use the current STIHL manual, ANSI Z133, and OSHA 29 CFR 1910.266 where its logging-work rules apply.

Before each job, inspect the chain brake, throttle interlock, chain catcher, handles, chain tension, bar rails, sprocket, and fuel and oil caps. Wear a helmet with face and eye protection, hearing protection, chainsaw chaps or trousers, gloves, and protective boots.

Assess tree lean, visible defects, wind, footing, overhead hazards, escape routes, and bystanders. Keep people outside the planned fall zone and clear of escape paths. Utility-line work belongs to qualified line-clearance workers. Stop if the site, saw, or your competence is not adequate for the task.

Use fresh fuel mixed with approved STIHL two-stroke oil at 50:1, unless the exact manual says otherwise. That is 20 mL of oil per 1 L of gasoline. Do not use straight gasoline or change the ratio based on an oil brand unless STIHL authorizes it; wrong fuel can cause severe engine damage.

Fit an approved bar and chain, sharpen the chain, and set cold-chain tension as the manual directs. Fill fuel and chain oil separately. Start on stable ground using the prescribed cold- or warm-start method, with the chain brake engaged. Confirm the chain does not move at idle and check oil delivery by the manual’s test procedure.

Field cutting and the C-M R’s role

A field scenario shows where the model difference matters: two trained crews may use the same approved bar and chain for similar work, but one crew operates regularly in cold weather. If the regional R model has heated handles, that feature may make it the more relevant choice for that crew. It does not change the felling plan or make a risky cut safe.

Keep a secure stance and two-handed grip. Plan each cut, engage the chain brake while walking or repositioning, and do not cut above shoulder height. Avoid the upper quadrant at the guide-bar nose. Contact there can cause rotational kickback, which can throw the bar rapidly toward you. A working chain brake reduces risk; it does not make nose contact safe.

For felling, use a trained plan and a clear escape route. Do not improvise hinge dimensions or force a cut beyond the bar and chain’s capability. There is no single hinge thickness or fastener torque that is safe for every tree or setup. Base decisions on the manual, tree assessment, and qualified judgment.

If the chain is dull or tension is wrong, stop and correct it. Do not push harder to make the saw cut. More force does not fix a poor chain condition and can undermine control.

Maintenance, sharpening, and M-Tronic service

Routine care preserves cutting performance and helps reveal faults before the next job. Both versions need the same basic chain, bar, and engine checks; the R model also has a heated-handle feature that should be handled according to its regional manual.

Set depth gauges with the correct gauge tool and the chain maker’s specification. A setting of 0.65 mm (0.025 in.) is common for STIHL 3/8-inch chain, but confirm the exact chain type rather than applying that number to every chain. Keep cutters even and inspect the bar groove and rails.

Check oil delivery and use approved bar-and-chain oil. Oil flow may be adjustable on applicable versions, but there is no single flow rate or oil viscosity that suits every temperature and model. Follow the manual’s test and adjustment steps.

Published reference values are approximately 2,800 rpm idle and 13,000 rpm maximum engine speed. Treat these as references, not targets to tune by ear. M-Tronic carburetion is not adjusted by turning conventional H/L screws; send performance or electronic-system faults to qualified service.

After use, engage the brake, shut down as directed, let the saw cool, then clean and inspect it. Check tension, cutters, depth gauges, bar groove and rails, air filter, and oil delivery. Record defects and remove an unsafe saw from service.

Storage and seasonal care

Storage means leaving the saw clean, safe, and ready for the next planned use. Follow the manual for fuel handling, cleaning, and long-term storage. Do not assume the C-M R needs a different fuel ratio or engine-care routine simply because it has heated handles.

Keep fuel fresh and correctly mixed, and store the saw in a safe place away from ignition sources. Before seasonal work, inspect the cutting system and safety controls again. If you are unsure whether the heating feature works or how it is operated, ask a STIHL dealer to check the exact model rather than guessing.

Conclusion: which MS 661 should you buy?

For cutting power, the stated specifications put the MS 661 C-M and C-M R in the same engine class. The decision is mainly about electrically heated handles: select the C-M R when you regularly work in cold conditions and confirm that feature on the regional model. Otherwise, the C-M may be the more direct fit.

Either way, match the bar and chain to the saw and the job, follow the current manual, and buy only when the model and equipment are clear. A suffix is not a substitute for checking the plate, approved parts, and your actual work needs.

FAQ: MS 661 C-M and C-M R

Is the MS 661 C-M R more powerful than the C-M?
Not according to the cited specifications. Both are listed at 91.1 cm³ and 5.4 kW (7.2 bhp). Confirm the figures for your regional model.

What does the R mean on the MS 661 C-M R?
On markets where that version is offered, it identifies electrically heated handles. Verify the equipment on the exact saw.

Do both versions use M-Tronic?
Yes. Both are M-Tronic versions. Do not adjust their carburetion with conventional H/L screws.

Can I use the same bar and chain on both?
Only if the exact combination is approved for each saw and the pitch, gauge, and drive-link count match. Check the manual and component markings.

What bar length is right for an MS 661?
STIHL lists options broadly around 50–90 cm (20–36 in.), depending on market. Choose by tree, cut plan, and operator capability, not displacement alone.

Is 3/8-inch pitch and .063-inch gauge correct?
That is a common MS 661 setup, but verify the bar stamp and chain part number before fitting a chain.

What fuel mix does the MS 661 use?
The specified mix is 50:1 with approved two-stroke oil, such as 20 mL oil per 1 L gasoline. Follow the exact manual and never use straight gasoline.

Does heated handles replace cold-weather gloves or safety gear?
No. Handle heating does not replace protective gloves, PPE, training, or safe operating practices.

Can I change the M-Tronic settings myself?
Do not adjust carburetion using conventional H/L screws. Follow the manual’s procedures and use qualified service for faults.

Is either version safe for utility-line tree work?
Utility-line work requires qualified line-clearance operations. A chainsaw model or heated-handle feature does not make that work suitable for an unqualified operator.

(This article was written by one of our staff writers, Marcus Thorne. Visit our Meet the Team page.)