What Is A Stihl Chainsaw Ignition Coil Air Gap (Spec Specs)
A STIHL chainsaw ignition-coil air gap is the small clearance between the ignition module and the flywheel magnets. Many STIHL saws use 0.2–0.3 mm (0.008–0.012 in.), but that range is not universal. Check the service information for your exact model and serial range before adjusting it; the wrong gap can cause poor spark or damage.
If a manual mentions an “air gap,” it can sound like a tiny detail with high stakes. The good news is that the term describes a measurable clearance, not a hidden electronic setting. Understanding where to measure it and how to confirm the correct specification helps you avoid guessing.
I teach this as two separate questions: What does the gap measure, and what does your particular saw require? The first answer is the same across this type of ignition system. The second depends on the model and ignition module.
Equipment Identification, Setup & Safety Preparation
The ignition air gap is the clearance from the ignition module’s pole faces to the flywheel’s magnet surfaces when those parts face each other. It lets the module work with the passing magnets to create ignition spark. Before you adjust it, identify your saw and find its model-specific service data.
What does the ignition-coil air gap measure?
The air gap measures the physical distance between the flat pole faces of the ignition module and the flywheel magnets. It is checked with the magnets positioned opposite the module. It does not measure the spark plug’s electrode gap, the distance from the coil to the cover, or a gap in the fuel system.
On many STIHL chainsaws, a commonly cited air-gap range is 0.2–0.3 mm (0.008–0.012 in.). Treat that as a general reference only. The correct value may differ by model, ignition module, or service information for a particular serial range.
| Measurement | Where it is checked | Common reference | What to verify |
|---|---|---|---|
| Ignition-module air gap | Between module pole faces and flywheel magnets | 0.2–0.3 mm on many saws | Exact model and serial-range service data |
| Spark-plug gap | Between the plug’s center and ground electrodes | Often 0.5 mm (0.020 in.) on STIHL saws | The saw’s manual and specified plug |
These values are not interchangeable. A plug gap set correctly does not confirm that the ignition module is positioned correctly, and vice versa.
Identify the saw and prepare it safely
Record the exact model and serial number, then use STIHL’s manual or service information for that saw. A parts listing or a specification for a similar-looking saw is not a safe substitute. If the correct air-gap value or tightening torque is not available, pause and obtain the right service data.
Before removing covers, wear eye and hand protection. Engage the chain brake, stop the engine, let it cool, and disconnect the spark-plug boot so the engine cannot start while you work. Keep the saw stable, and follow the manual for cover removal and access.
- Takeaway: Confirm the specification first; do not set the gap by appearance or by a value found for a different model.
Ignition Air-Gap Adjustment and Functional Test
To adjust the gap, position the flywheel magnets opposite the module poles, use the specified gauge or spacer, and tighten the module fasteners to the model’s stated torque. Then rotate the flywheel by hand and check that the clearance stays even and no parts touch.
Step-by-step adjustment
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Access and inspect. Remove only the covers required by the service procedure. Check for loose module fasteners, damaged wires, debris, visible flywheel damage, or magnets that appear loose or contaminated. Do not continue if a component is damaged or you are unsure how it is retained.
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Align the magnets. Turn the flywheel by hand until its magnets are opposite the ignition-module pole faces. This is the point where the air gap is measured.
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Set the specified clearance. Loosen the module fasteners enough to position it. Place the manual-approved, nonmagnetic gauge or suitable spacer between the pole faces and magnets. The magnets may pull the flywheel toward the module as you position it.
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Tighten to specification. Keep the gauge in place while tightening the fasteners. Use the torque value in the service information for your exact saw; do not guess or assume that a general torque applies.
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Recheck the full rotation. Remove the gauge and rotate the flywheel through a complete turn by hand. Check the gap when the magnets return to the module. It should remain consistent, with no contact. If it changes noticeably or anything touches, stop and inspect the alignment and components.
A generic business card is not a reliable substitute for the specified gauge: its thickness can vary, and the service procedure may call for a different tool. Nor should you substitute a random feeler gauge if the manual specifies another method or tool.
Why the gap matters
The ignition module and flywheel work together to produce spark at the right point in the engine cycle. If the gap is too wide, the ignition system may produce a weak or intermittent spark. That can contribute to poor running or starting trouble, though those symptoms can have other causes.
A gap that is too small can let the flywheel strike the module as parts flex or the crankshaft moves. Contact can damage the module or flywheel and may lead to sudden engine failure. The goal is not “as close as possible”; it is the exact model-specified clearance.
Field-style diagnostic examples
These examples are common diagnostic situations, not reports about a particular saw. They show why checking the measurement and other parts is better than repeatedly changing the gap.
- The saw has no spark after module work: First confirm the air gap against the model’s service data and inspect wiring and connections. A correct gap alone does not prove the module, stop switch, or spark plug is working.
- The flywheel rubs after adjustment: Stop turning it. Check alignment, the gap around the rotation, and any visible damage. Do not run the saw to see whether the rubbing stops.
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The saw still starts poorly with the gap set correctly: Avoid making the gap smaller or larger at random. Inspect the plug, wiring, stop switch, module, and flywheel as directed by the service procedure.
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Takeaway: Set the gap to the manual, then verify clearance through a full hand rotation before reassembly.
Troubleshooting, Maintenance & Specification Checks
Air-gap problems can affect spark, but a starting or running issue does not prove the gap is wrong. Use the correct model specification, inspect related ignition parts, and avoid repeated adjustments. A measured gap is one useful check within a wider diagnosis, not a complete test of the ignition system.
Specification and symptom checks
| What you find | What it may indicate | Sensible next step |
|---|---|---|
| Gap differs from the specified value | Module position may need correction | Recheck the model and serial range, then reset per service data |
| Gap varies as the flywheel turns | Misalignment, uneven clearance, or a component issue | Stop and inspect; do not operate with possible contact |
| Gap is correct, but there is still no spark | A different ignition part or connection may be at fault | Check plug, wiring, stop switch, module, and flywheel |
| Module or flywheel looks damaged | Adjustment alone may not resolve the problem | Follow service guidance or have the saw inspected |
A spark-plug gap is a separate measurement, commonly listed as 0.5 mm (0.020 in.) for many STIHL saws. Confirm the correct plug and plug gap in the model manual. Do not alter the coil air gap to compensate for a plug that is worn or incorrectly gapped.
Fuel mix and cutting setup do not determine ignition-module air gap. Many current STIHL two-stroke saws use 50:1 premix with approved two-stroke oil, but the saw’s instructions govern. Likewise, bar length, chain pitch, chain gauge, and drive-link count must suit the saw and bar; they are separate specifications.
When to stop and seek help
Stop work if the service value is unclear, a magnet is loose, the flywheel or module is damaged, the gap cannot be made even, or the flywheel contacts the module. These are not problems to solve by forcing parts or using a thinner spacer. A STIHL dealer or qualified small-engine technician can identify the correct parts and service procedure.
If you complete the adjustment and the symptom remains, do not keep moving the module in tiny increments. Recheck the plug, wiring, stop switch, coil, and flywheel using the manual’s diagnostic steps. Persistent faults may require tests or tools beyond a visual gap check.
- Takeaway: A correct air gap is important, but it cannot rule out faults elsewhere in the ignition system.
Reassembly, Storage & Seasonal Care
Once the gap is confirmed, reinstall the covers and guards required by the service procedure before starting the saw. Reconnect the spark-plug boot only after reassembly. Test outdoors with the saw securely controlled, following the operator’s manual; never run it with covers removed or hands near exposed moving parts.
Reassemble and test
Before the test start, make sure fasteners are secure and that no tools or spacers remain inside the saw. Refit all removed covers and guards, then reconnect the spark-plug boot. Start the saw outdoors, following the normal starting procedure and keeping the chain clear of people and objects.
If it does not start or run properly, stop and diagnose the cause rather than immediately readjusting the gap. Do not adjust the air gap with the engine running, with the spark-plug boot connected, or while the saw is operating without its covers or guards.
For storage or seasonal care, the air gap does not need routine adjustment simply because the saw has been stored. If you remove or replace the ignition module, flywheel, or related parts, inspect the gap and follow the model-specific service procedure before use.
- Takeaway: Reassemble fully before testing, and treat a new ignition-part installation as a reason to verify—not guess at—the gap.
Frequently Asked Questions
These short answers cover the key measurement and safety points. For a final specification, use service information for your exact STIHL model and serial range, since a general range cannot confirm what every saw requires.
What is the STIHL chainsaw ignition-coil air gap?
It is the clearance between the ignition module’s pole faces and the flywheel magnets when they face each other.
What is the usual STIHL ignition air-gap specification?
Many saws use 0.2–0.3 mm (0.008–0.012 in.), but this is not a universal specification. Check the exact model’s service data.
Where do I measure the air gap?
Measure between the ignition-module pole faces and the flywheel magnet surfaces, with the magnets aligned opposite the module.
Is the ignition air gap the same as spark-plug gap?
No. The air gap is between the module and flywheel magnets. Plug gap is between the spark plug’s electrodes.
Can I use a business card to set the gap?
Do not assume a business card is suitable. Use the gauge or spacer specified for your saw’s service procedure.
Can I use a feeler gauge?
Only if it matches the model’s specified method and clearance. Do not substitute a generic gauge for the service instructions.
What happens if the ignition gap is too small?
The flywheel may strike the module as parts move or flex, which can damage the module or flywheel.
What happens if the gap is too large?
The ignition may produce weak or intermittent spark. Other ignition faults can cause similar symptoms.
Should I adjust the gap if the saw will not start?
Not without checking the specified gap and other possible causes, such as the plug, wiring, stop switch, module, or flywheel.
Do all STIHL chainsaws use the same air-gap specification?
No. The required clearance is model- and ignition-module-specific. Check the service information for the exact saw.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
