Stihl BG 56 C Spark Plug Gap (Replacement Guide)
The STIHL BG 56 C spark plug gap is 0.5 mm (0.020 in). The specified plug is an NGK CMR6H, but check your blower’s manual and model details before fitting one. Work on a cool engine, measure with a feeler gauge, start the plug by hand, and use the manual’s tightening instructions.
Do you want a blower that starts reliably when yard work begins, rather than one that turns a simple tune-up into a repair? Checking the spark plug gap is a small job, but the right plug, careful handling, and safe installation matter. Here’s how to inspect or replace the plug on a BG 56 C.
Equipment Setup and Safety Preparation
Before starting, place the blower outdoors on a stable surface and let the engine cool. Keep it away from flames, sparks, and other ignition sources. Wear eye protection and gloves. Switch the ignition off, then pull the spark-plug boot straight off the plug.
Check the model label and manual before buying a replacement. The specified plug for the BG 56 C is NGK CMR6H, and the listed electrode gap is 0.5 mm, or 0.020 in. If the manual for your machine lists a different plug, follow that information rather than relying on a general guide.
| Item to check | BG 56 C reference | What to do |
|---|---|---|
| Engine type | Single-cylinder, air-cooled, two-stroke | Confirm the model in your manual |
| Displacement | 27.2 cm³ | Use it as a model-identification check |
| Specified spark plug | NGK CMR6H | Verify against your machine’s manual |
| Electrode gap | 0.5 mm (0.020 in) | Measure with a feeler gauge |
| Fuel mixture | 50:1 gasoline to STIHL two-stroke oil, or approved equivalent | Follow the manual and fuel-oil product instructions |
A matching plug and gap help the ignition system produce a spark as designed. They do not prove that a no-start problem is caused by the plug. Fuel condition, air supply, and other ignition parts may also need attention if the blower still will not run.
Blower Operation and Work-Area Safety
A spark-plug check is a service task, not a reason to run the blower indoors. Keep inspection and testing outdoors, with the blower on stable ground and pointed away from people, animals, and loose debris. Stop if you see fuel leakage or notice damage that makes operation unsafe.
Before removing the plug, clean loose dirt from the area around it. This helps keep debris from falling into the cylinder when the plug comes out. Use a suitable spark-plug wrench, and avoid pulling on the ignition lead when removing the boot.
After servicing, refit the boot securely before starting the engine. Test the blower outdoors and follow the starting steps in its manual. Keep hands and clothing clear of moving parts, and stop the engine if it runs abnormally or if you find a fuel leak.
Spark-Plug Maintenance and Inspection
The electrode gap is the small space between the center electrode and the ground electrode at the tip of the plug. On the BG 56 C, the specified gap is 0.5 mm (0.020 in). A feeler gauge checks that space; visual judgment alone is not precise enough.
How to inspect and set the gap
With the engine cool and ignition off, remove the boot and clean around the plug. Unscrew the plug carefully. Look for a cracked insulator, damaged electrodes, heavy deposits, or other visible damage. Replace a damaged plug with the correct type rather than trying to repair it.
Insert the 0.5 mm feeler gauge between the electrodes. It should pass with light contact, not require force. If the gap is too wide or too narrow and the plug is otherwise serviceable, adjust the ground electrode slightly with a proper plug-gap tool. Do not pry against the center electrode or use a screwdriver. Recheck the gap after each small adjustment.
| Inspection result | Recommended action |
|---|---|
| Gap measures 0.5 mm and plug is undamaged | Reinstall or keep in service, following the manual |
| Gap is off, but the plug is undamaged | Adjust the ground electrode gently, then measure again |
| Cracked insulator or damaged electrode | Replace with the plug specified for your blower |
| Heavy deposits or repeated fouling | Replace if needed, then check fuel and engine condition if the problem returns |
| Plug type does not match the manual | Do not assume the gap alone makes it suitable; verify the correct plug |
A gap check is useful maintenance, but it is not a cure for every starting fault. If a correctly gapped plug does not solve the problem, avoid repeated adjustment. Check the starting procedure and fuel, and consult the manual or a service dealer if the cause is unclear.
How to replace and reinstall the plug
If replacing the plug, confirm that the new one is the type listed for your specific BG 56 C. Do not assume that a plug with the same appearance or a similar name is interchangeable. Check its condition and gap before fitting it.
Start the plug into the cylinder head by hand. It should turn freely at first. If it binds, stop, back it out, and realign it. A plug started at an angle can damage the cylinder-head threads; forcing it can turn a routine replacement into a costly repair.
Once the plug is seated, tighten it only as directed in the manual. I do not give a universal torque value here because the machine’s own instructions should control. Refit the boot securely. Keep the removed plug until the work is complete so you can compare it with the replacement if needed.
Practical service scenarios
These examples show how to apply the checks without assuming a single cause for every starting problem.
- The blower ran last season but now starts poorly. I would first check that the machine is the BG 56 C, inspect the plug, and measure its gap. If the plug is damaged or worn, fit the specified replacement and follow the manual’s installation instructions. If the blower still runs poorly, check the other items named in the manual rather than widening the gap.
- A new plug appears to fit but will not turn freely by hand. Stop. Do not use a wrench to force it into the head. Remove it, check that it is the correct plug, and restart it straight by hand. If it still binds, get help before damaging the threads.
- The plug looks clean and measures 0.5 mm, but the engine will not start. The gap is within specification, but that does not rule out a fuel, air, starting, or ignition issue. Follow the model’s troubleshooting steps instead of changing the gap without evidence.
These are diagnostic examples, not reports of one confirmed repair. The key is to change one thing at a time and keep the plug specification and installation steps tied to the machine’s manual.
Shutdown, Cleaning, and Seasonal Storage
After the test, switch off the blower and let it cool before touching the plug area again. Clean the exterior and air-intake area as described in the manual. A service log can help you remember when you inspected or replaced the plug and what you found.
For fuel, use the manual’s specified 50:1 gasoline-to-STIHL two-stroke-oil mixture, or an approved equivalent mix. Measure the gasoline and oil accurately; do not estimate the ratio by eye. Follow the fuel and oil instructions for mixing and storage, and use the blower manual’s steps for seasonal storage.
If the same plug becomes fouled again soon after replacement, note the fuel used, starting behavior, and any visible deposits. Repeated fouling may point to a condition beyond plug gap. Avoid repeated plug changes without checking the troubleshooting guidance or asking a qualified service dealer.
Conclusion and Frequently Asked Questions
The reliable approach is simple: verify the model and plug, set the gap to 0.5 mm (0.020 in), and install the plug without forcing it. Use the manual for tightening and operating instructions. If the blower still has a starting problem, treat the plug as one diagnostic check, not the only possible cause.
What is the spark plug gap on a STIHL BG 56 C?
The specified gap is 0.5 mm, or 0.020 in. Confirm the specification in the manual for your exact blower.
Which spark plug does a BG 56 C use?
The specified plug is an NGK CMR6H. Check your machine’s manual before buying or fitting a plug.
Can I use another spark plug if it has the same gap?
Do not choose a plug based on gap alone. Use the plug type listed for your model and market in the manual.
What tool should I use to check the gap?
Use a feeler gauge that measures 0.5 mm. A visual estimate is not an accurate measurement.
Can I adjust the gap with a screwdriver?
No. Use a proper plug-gap tool to make small adjustments to the ground electrode. Avoid contact that could damage the center electrode.
How tight should I install the spark plug?
Follow the tightening instruction in the BG 56 C manual. Do not guess or exceed its instruction.
What if the plug will not turn by hand?
Stop and remove it. Check that it is the correct plug and aligned straight. Do not force it with a wrench, because that can damage the cylinder-head threads.
Does a correct gap guarantee the blower will start?
No. A correct gap is one part of ignition service. Fuel, air supply, starting steps, or another fault may still prevent a start.
What fuel mix does the BG 56 C use?
The specified mixture is 50:1 gasoline to STIHL two-stroke oil, or an approved equivalent. Follow the manual and the fuel and oil instructions.
Should I replace a plug with heavy deposits?
Inspect it for damage and follow the manual’s maintenance guidance. If deposits return after replacement, check the fuel and troubleshooting guidance rather than repeatedly changing the plug.
(This article was written by one of our staff writers, Harrison Croft. Visit our Meet the Team page.)
