Stihl MS 251 C Parts Diagram (Service Guide)
To identify the correct parts for an MS 251 C, match the saw’s full model marking and serial number to the STIHL parts diagram for its market and production version. Then check each item against the diagram and the saw itself. The “C” suffix alone does not confirm bar, chain, sprocket, or replacement-part compatibility.
A parts diagram is useful years after a saw was made, but only when it matches the right version. A familiar-looking component can differ by production run or market, and a wrong order can cost time as well as money. I use the diagram as a compatibility check, not as a substitute for the saw’s manual or a hands-on inspection.
For a dependable match, write down the model marking and serial number, then ask a STIHL dealer to check them against the official parts information. Before ordering cutting parts, also read the markings on the bar and chain. Those markings answer questions the model name alone cannot.
MS 251 C Parts Identification, Setup & Safety Checks
This section explains how to use the parts diagram to identify the saw and its main assemblies. Start with the product marking and serial number, then confirm the diagram’s model and version before choosing parts. The MS 251 has a 45.6 cm³ engine rated at 2.2 kW (3.0 bhp).
Find the right diagram and part
An exploded-view diagram shows assemblies separated into individual pieces, with callout numbers that point to a parts list. The callout is not always the same as the part number. Use the corresponding list, and confirm the listed part against your saw’s version before buying.
- Clean the identification area and record the full model marking and serial number. Do not rely on a seller’s title or a partial “MS 251” label.
- Use STIHL’s official parts information or have an authorized dealer search the serial number. Ask the dealer to confirm the applicable production version and market.
- Open the matching illustration, find the assembly, and note the callout and listed part number. Check for replacement or superseded numbers with the dealer.
- Compare the proposed part with the existing one: shape, mounting points, connections, and relevant dimensions. Stop if the diagram, list, and saw do not agree.
The “C” in a model name is not enough to identify a specific feature package or component. STIHL naming and equipment can vary by market and version. Confirm any suffixes from the saw’s label and the matching manual rather than inferring features from the letter.
| Diagram area | Examples of parts shown | Check before ordering |
|---|---|---|
| Engine and crankcase | Covers, seals, cylinder-related components | Model, serial range, and exact diagram |
| Clutch and chain drive | Clutch-side parts, sprocket, drum, cover | Sprocket type and compatibility with the saw |
| Guide bar and chain | Bar, chain, tensioning parts | Bar mount, pitch, gauge, and drive-link count |
| Fuel and air system | Filter, fuel lines, carburetor-related parts | Version and market; verify service need first |
| Handles and controls | Switches, guards, handles, brake parts | Exact fit and safety function |
Inspect the saw before service
A parts diagram can help locate a part, but it cannot show whether the saw is safe to run. Before starting, inspect the chain brake, throttle lockout, chain catcher, handles, bar, chain tension, and visible fuel or oil leaks. If a safety control is damaged or does not work, do not use the saw until it is repaired.
Wear a helmet with face and eye protection, hearing protection, chainsaw-rated leg protection, gloves, and boots when operating the saw. For felling, assess lean, wind, overhead hazards, targets, and escape routes first. A diagram is a reference for service, not a guide to making an unsafe cut.
Field Cutting and Property-Maintenance Procedure
This section covers operating checks that matter when returning the saw to service after parts work. Use the operator’s manual for the starting method and controls, and test safety features before cutting. Correct assembly matters: an incorrectly fitted brake or chain-drive part can create a serious hazard.
Starting and operating checks
Start only with the saw assembled and inspected. Follow the manual’s cold- or warm-start procedure, using a secure ground-start position or an approved leg-through-handle method. Engage the chain brake for starting and release it only when ready to cut. Never drop-start the saw.
During cutting, keep both hands on the saw and work below shoulder height with sound footing. Plan the cutting sequence and keep people, structures, and utilities clear of the work area. Avoid contact between the wood and the guide-bar nose. Contact with the upper quadrant of the bar can cause rotational kickback and severe injury.
When checking a repaired saw, do not bypass the brake or other safety parts to “see if it runs.” If the brake does not engage and release as intended, or the chain moves at idle, stop and consult the manual or a qualified STIHL service provider. Do not attempt to correct a fault with an unverified adjustment.
A practical parts-diagram example
These are illustrative service situations, not reports of a specific repair. They show how to use the diagram without guessing at fit or cause.
A saw needs a replacement sprocket. The owner first checks the serial number and locates the chain-drive illustration. The dealer confirms the correct version and sprocket listing, then checks that the replacement matches the drive system. Choosing a sprocket by appearance alone would leave compatibility uncertain.
Another saw needs a new chain after wear. The owner reads the bar stamp and chain packaging, then confirms pitch, gauge, and drive-link count. The parts diagram may help identify related parts, but it does not make those chain dimensions universal across MS 251 configurations.
Chain, Bar, Carburetor & Routine Maintenance
This section focuses on parts most likely to be checked during routine service. Cutting equipment varies by configuration, so use the bar and chain markings and the correct manual. Do not assume a single chain size, raker setting, carburetor adjustment, or oil-flow rate applies to every MS 251 C.
Match the bar, chain, and sprocket
Pitch is the chain’s size class, gauge is the thickness of the drive links, and drive-link count is the number of links that run in the bar groove. Read the bar stamp and chain package, then confirm all three details before ordering. Also check the bar mount and sprocket compatibility.
| Check | Where to verify | Why it matters |
|---|---|---|
| Bar mount | Existing bar and matching saw information | Bar must fit the saw’s mounting arrangement |
| Chain pitch | Bar stamp and chain packaging | Must match the sprocket and cutting system |
| Chain gauge | Bar stamp and chain packaging | Must fit the bar groove |
| Drive-link count | Existing chain or chain packaging | Must match the bar length and setup |
| Sprocket compatibility | Official parts information or dealer | A matching pitch alone does not prove fit |
Do not force a dull or incorrectly tensioned chain through wood. A dull chain can increase heat and cutting effort; poor tension raises the risk of derailment. Use the chain maker’s matching depth-gauge tool for raker clearance. There is no single safe value to apply to every chain without checking its specifications.
Check lubrication and service parts
Use bar-and-chain oil suited to the ambient temperature. Clean the bar groove and oil hole when servicing, and verify that oil reaches the chain using the manual’s procedure. Do not assume the oil system is working just because the reservoir is full.
For routine care, stop the engine, engage the brake, allow the saw to cool, and clean the air filter as directed. Inspect the bar, chain, sprocket area, and fasteners. Follow the manual for sharpening, tension checks, service intervals, and fastener torques; do not substitute a guessed torque or generic adjustment.
The idle speed is approximately 2,800 rpm. Carburetor settings and any maximum-speed limit can depend on the model and market. Use the correct service data and a tachometer when adjustment is required; do not tune by ear. If the saw runs poorly or the chain moves at idle, have the cause checked rather than adjusting blindly.
Storage, Fuel Management & Seasonal Care
This section covers fuel and storage steps that help protect the engine and make later parts checks easier. The MS 251 is a two-stroke saw and needs the specified fuel mixture. For the fuel ratio and storage process, follow the manual supplied for the saw and use fresh, correctly mixed fuel.
Fuel and storage
STIHL specifies a 50:1 mix with suitable STIHL two-stroke oil. Measure carefully and use fresh fuel prepared for that ratio. Do not use straight gasoline or an unverified ratio: too little two-stroke oil can cause severe engine damage, including piston seizure.
Before storing the saw, clean it and inspect for damage or leaks. Follow the manual’s directions for fuel and seasonal storage, since recommended steps can depend on the fuel used and the storage period. Keep the saw in a secure, dry place, away from children and ignition sources. Record any part numbers or service work for future reference.
When to involve a dealer
A dealer is especially useful when a diagram shows multiple versions, a part number has been replaced, or the serial range is unclear. Bring the model marking, serial number, and photos of the existing part and its mounting area. For a chain or bar, include clear photos of the bar stamp and chain packaging.
A dealer should also handle work that requires model-specific service data or specialized tools, such as uncertain carburetor adjustment or repair of the chain brake. If the saw’s markings are damaged, the part does not match the diagram, or a safety control has failed, stop rather than fitting a near-match.
Frequently Asked Questions
These short answers address common questions about identifying parts, checking compatibility, and servicing an MS 251 C. Confirm uncertain details with the matching STIHL manual or dealer, especially when serial range, market, or cutting equipment may affect the answer.
How do I find the correct MS 251 C parts diagram?
Record the full model marking and serial number, then use STIHL’s official parts information or ask a dealer to identify the matching version. Verify the diagram title and parts list before ordering.
Does the “C” suffix identify a specific replacement part?
No. The suffix alone does not confirm which part fits or what equipment is on a particular saw. Check the complete model marking, serial number, market version, and matching diagram.
Where can I find the serial number?
Check the saw’s product identification markings and the operator’s manual for their location. Clean the area gently and record the number exactly; do not confuse it with a bar or component marking.
Can I order a chain by the MS 251 model name?
Not safely. Confirm pitch, gauge, and drive-link count from the bar stamp and chain packaging, and verify the sprocket and bar setup. These details can vary by configuration.
What is the MS 251 engine size and output?
The engine displacement is 45.6 cm³, and rated output is 2.2 kW (3.0 bhp). These specifications do not determine which bar, chain, or replacement part fits.
What fuel mixture does the MS 251 use?
Use a 50:1 mixture with suitable STIHL two-stroke oil and fresh fuel, following the saw’s manual. Do not run straight gasoline or guess at the ratio.
What is the correct idle speed?
The idle speed is approximately 2,800 rpm. Use model-specific service information for adjustment, and do not tune by ear. If the chain moves at idle, stop and have the saw checked.
Can I use one raker-clearance value for every chain?
No. Raker clearance depends on the chain specification. Use the chain maker’s matching depth-gauge tool and instructions instead of applying a universal value.
How can I tell whether the chain is getting oil?
Use the inspection procedure in the operator’s manual and confirm oil reaches the chain. Check the oil supply, bar groove, and oil hole if lubrication seems poor; consult a dealer if the cause is unclear.
Which parts should I avoid fitting without confirmation?
Do not guess on chain-brake parts, clutch or sprocket components, carburetor parts, or any part that differs from the correct diagram. Confirm the part number and fit with STIHL’s official information or a dealer before use.
(This article was written by one of our staff writers, Elliott Fowler. Visit our Meet the Team page.)
