Stihl Chainsaw Spark Plug Gaps (Spec Chart)
Set the spark-plug gap on a STIHL chainsaw to the specification for its exact model and plug. A gap of 0.5 mm (0.020 in) is common, but it is not universal. Check the saw’s manual or STIHL service data before adjusting. If the gap or plug is wrong, don’t keep cutting to see whether the problem clears.
If you’re getting a saw ready while family or work waits, it’s tempting to use the first gap value you find online and head out. Take a moment to identify the model first. The right gap is set by the engine and ignition specification, not by the bar, chain, or wood you plan to cut.
I use a wire gap gauge and the model’s manual rather than relying on memory. That small check can help prevent misdiagnosis, but it cannot fix a damaged plug or another ignition fault. Here’s how to find the correct value and check it safely.
Identify the STIHL Model and Prepare the Saw Safely
The model number is the starting point for finding the correct spark-plug gap. Record it, and note the serial number if available, before choosing a plug or adjusting an electrode. STIHL saws can have different engine and ignition specifications, so a value that fits one model may not fit another.
Look for the model identification on the saw’s label or housing. Then find the matching instruction manual or STIHL service information. Check that the plug type listed there matches the plug you plan to install. Thread size alone does not confirm that a plug has the right type or heat range.
| Item to check | What you can use as a starting point | What to confirm |
|---|---|---|
| Spark-plug gap | 0.5 mm (0.020 in) is common on many STIHL saws | Exact value for your model and specified plug |
| Spark-plug type | No universal plug type | Plug type and heat range listed for the saw |
| Installation | No universal torque value | Manual’s seating and tightening instructions |
| Fuel mix | 50:1 for two-stroke saws whose manual calls for that mix | Manual and oil-label directions |
This is a reference table, not a model-by-model specification chart. It does not establish 0.5 mm as the right setting for every STIHL chainsaw. A model’s manual is the authority for its gap, plug, and installation instructions.
Before service, switch off the saw, engage the chain brake, let the engine cool, and disconnect the spark-plug boot. Wear eye protection and gloves. Brush dirt away from the plug area before removing the plug; debris that falls into the cylinder can cause damage.
Key takeaway: Identify the saw and verify its exact plug specification before you touch the gap.
Verify Spark-Plug Gap and Perform a Controlled Start
The spark-plug gap is the distance between the center and ground electrodes. To check it, use a wire gap gauge and compare the measurement with the value for your exact model. Adjust only when needed, and only to that value; do not use a common setting as a substitute for model data.
- Check the plug number. Compare the plug installed in the saw with the type named in the manual. If it differs, do not assume it is suitable because it screws into the cylinder.
- Inspect before measuring. Look for a cracked insulator, damaged threads, badly worn electrodes, or heavy deposits. Replace a damaged or excessively worn plug rather than trying to correct it by changing the gap.
- Measure the gap. With the plug out and cool, pass the correct wire gauge between the electrodes. Use the gauge size that matches the manual’s specified gap.
- Adjust carefully if needed. Use a suitable plug-gap tool to move the ground electrode in small steps. Avoid levering against the center electrode or porcelain insulator. Recheck the gap after each adjustment.
- Install as directed. Follow the manual’s instructions for seating and tightening the plug. Do not apply a generic torque value; the required procedure can depend on the model and plug.
- Reconnect and test. Refit the boot, then start the saw outdoors using the manual’s cold- or warm-start steps. Check for a steady idle and confirm the chain does not move at idle. Check chain-brake function as the manual directs.
An incorrect gap, wrong plug, loose plug, or damaged insulator can contribute to hard starting, misfiring, overheating, or ignition failure. If the saw stalls or runs erratically during cutting, stop work. A running fault can affect control; don’t keep cutting or widen the gap to try to compensate.
Shop-style example 1: A saw is hard to start after a plug change. The useful first checks are whether the installed plug matches the model specification and whether its measured gap matches the manual. Changing the gap by guesswork can add another fault instead of finding the cause.
Shop-style example 2: A saw starts but then misfires under load. If the plug is the correct type and its gap is correct, the next step is diagnosis, not repeated gap changes. Persistent misfiring needs attention before the saw returns to cutting.
These are examples of a checking process, not records for a particular STIHL model. They show why the specification and the plug’s condition both matter.
Key takeaway: Measure, adjust only to the model’s value, reinstall by the manual, and stop if the saw still runs abnormally.
Inspect the Plug and Diagnose Ignition Problems
A gap check is one part of diagnosis, not a repair for every starting or running problem. Inspect the plug and its fit, confirm the model-specific part, and consider what changed before the fault began. If the saw still misfires or stalls with a correct plug and gap, stop and investigate instead of altering the setting again.
A plug that is wet, sooty, worn, cracked, or loose may point to a condition that needs more than gap adjustment. Deposits can affect performance, but appearance alone does not prove a single cause. Don’t assume that cleaning or resetting the gap will fix a fault without checking the plug’s condition and the manual’s guidance.
Fuel mix can also matter when a saw is hard to start or runs poorly. For STIHL two-stroke saws whose manuals specify STIHL MotoMix or premix, the standard ratio is 50:1: 50 parts gasoline to 1 part approved two-stroke engine oil. Follow the saw manual and oil label; do not apply that ratio to a model whose instructions say otherwise.
Keep spark-plug issues separate from chain and engine settings. Bar length, chain pitch, gauge, drive-link count, idle speed, and maximum speed are model- or setup-specific items, not values determined by the plug gap. Use the saw’s manual to check each one.
Key takeaway: If the specified plug and gap are correct but the fault remains, diagnose the underlying problem rather than changing the gap.
Clean, Record, and Store the Saw for Seasonal Care
A short service record helps you repeat the right setting later. Write down the saw model, plug type, specified gap, date checked, and any plug replacement. This is especially useful when a saw is used only now and then, because it keeps a past measurement from being mistaken for a universal STIHL specification.
After the test, shut down the saw and let it cool. Clean debris from around the plug and air intake without pushing dirt into the cylinder. Store the saw as directed in its manual, and keep the model’s service information with your maintenance notes.
If the saw did not idle normally, the chain moved at idle, or it stalled or misfired, don’t return it to cutting until the fault is resolved. A correct gap is not proof that the ignition system or engine is otherwise sound. Get qualified service if you cannot identify the cause or safely complete the repair.
Key takeaway: Record the setting and service date, then address any running fault before the next cutting session.
Frequently Asked Questions
These answers cover the most common gap checks and related questions. For any value that depends on a specific saw, use its model-matched manual or STIHL service data. Do not treat a general reference as a replacement for the engine’s specification.
What is the spark-plug gap on a STIHL chainsaw?
Many STIHL chainsaw specifications use 0.5 mm (0.020 in), but that is a common value, not a universal one. Check the manual for your exact model and specified plug before measuring or adjusting. If you cannot confirm the value, do not guess.
Can I set every STIHL chainsaw plug to 0.5 mm?
No. Although 0.5 mm (0.020 in) is common, STIHL saws do not all share one spark-plug specification. The model’s engine and ignition requirements determine the gap. Look up the exact model before setting it, and use the matching plug type.
How do I find the correct gap for my STIHL model?
Read the model identification on the saw, then find its instruction manual or STIHL service data. Check the spark-plug section for both the plug type and gap. If the saw has a serial number, keep it available when checking service information or asking a dealer.
What tool should I use to measure the gap?
Use a wire spark-plug gap gauge that includes the size specified for your saw. Slide the correct wire between the electrodes without forcing it. If the gap needs adjustment, use a suitable plug-gap tool and move the ground electrode carefully; avoid pressure on the center electrode or insulator.
Can I use a plug with the same thread size?
Not on thread size alone. A spark plug also needs to match the type and heat range specified for the saw. An unsuitable plug may fit the cylinder but still be wrong for the engine. Check the model’s manual before installing a replacement.
What should I do if the plug gap is wrong?
If the plug is correct and undamaged, adjust the ground electrode carefully to the model’s specified value, then measure again. Replace the plug if it is damaged or excessively worn. If the gap is already correct but the saw runs poorly, diagnose the fault instead of changing it.
Is the fuel mix 50:1 for every STIHL chainsaw?
No ratio should be assumed without checking the manual. For STIHL two-stroke saws whose instructions specify STIHL MotoMix or premix, the standard ratio is 50:1, or 50 parts gasoline to 1 part approved two-stroke oil. Follow the saw manual and oil label.
What if my STIHL chainsaw still misfires with the correct gap?
Stop using the saw until the problem is diagnosed. Confirm the plug type, condition, fit, and model-specific gap, but do not keep adjusting a correct gap to mask the fault. If the saw continues to misfire, stall, or run erratically, seek qualified service.
(This article was written by one of our staff writers, David Hensley. Visit our Meet the Team page.)
