Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
Changing a mower spark plug is about ten minutes of work wrapped in twenty minutes of looking things up, and the looking up is the part that matters. Briggs & Stratton's own instructions are short: disconnect the lead, clean around the plug, unscrew it with a spark plug socket, look at it, set the gap on the new one, screw it in without over-tightening, put the lead back. Toro's operator manual for the 22in Recycler adds the interval — replace the spark plug every 100 hours — and tells you to tighten it with a torque wrench. None of that is difficult. What trips people up is that the two numbers in the job, the gap and the tightening torque, are not the same for every engine.
So this page publishes the method and refuses to publish those two numbers. Briggs & Stratton says plainly that your engine repair manual gives the correct gap for your engine, and to contact a dealer if you do not have one; its own charts split by engine family and even by build date code. That is not a gap in this page — it is the honest answer, and a page that guessed a number for you would be worse than no page. What you get here instead is the sequence, the two manufacturer warnings that people actually get wrong (never blast a plug with abrasives, never re-gap a platinum or iridium plug), and a clear instruction about where your engine's own numbers live.
Necessary equipment
| Item | Note |
|---|---|
| Spark plug socket | Briggs & Stratton tells you to use a spark plug socket. |
| Torque wrench | Toro tells you to use a torque wrench for the spark plug. |
| Spark plug gauge | Briggs & Stratton tells you to use a spark plug gauge for the gap. |
| The documentation for your engine | The documentation gives the spark plug, the gap and the torque for your engine. |
| Clean cloth | A clean cloth removes the dirt near the spark plug. |
| Extension bar optional | An extension bar gives you access to a deep spark plug. |
| Flashlight optional | A flashlight helps you find a spark plug in a dark position. |
| New spark plug for your engine material | The part number is different for each engine model. |
Find the correct spark plug for your engine
Estimated 13 min to 31 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
Source: How do I check, clean and change small engine spark plugs? · tier 1 · accessed 2026-07-29
- Find the model number of the engine.3mReport a problem with step 1, Find the correct spark plug for your engine
- The number is usually on a label on the engine.
- The number on the mower deck is not the engine number.
- Write the number in your records.
USE ONLY THE SPARK PLUG THAT YOUR DOCUMENTATION GIVES.
Briggs & Stratton says that an incorrect spark plug can damage the engine.
- Get the correct spark plug for your engine from the documentation.4mReport a problem with step 2, Find the correct spark plug for your engine
- Briggs & Stratton gives a different plug for each engine family.
- Briggs & Stratton also tells you to speak to a dealer if you are not sure.
- Get the gap value for your engine from the documentation.3mReport a problem with step 3, Find the correct spark plug for your engine
- Briggs & Stratton sends you to the repair manual for your engine.
- This page does not print a gap value for your engine.
- Get the torque value for your engine from the documentation.2mReport a problem with step 4, Find the correct spark plug for your engine
- This page does not print a torque value for your engine.
- Speak to a service dealer if the documentation gives no value.
- Get a new spark plug before you start the work.1mReport a problem with step 5, Find the correct spark plug for your engine
- A mower with no spark plug cannot run.
Isolate the mower
Estimated 3 min to 31 min
DISCONNECT THE LEAD FROM THE SPARK PLUG BEFORE YOU TOUCH THE ENGINE.
The engine can start. The blade turns with the engine and can cut your hand.
- Set the engine control to STOP.<1mReport a problem with step 1, Isolate the mower
- Wait until the engine stops.
- Disconnect the lead from the spark plug.<1mReport a problem with step 2, Isolate the mower
- Toro tells you to do this before all maintenance work.
- Briggs & Stratton gives this as the first action of a spark plug service.
- Honda calls the same part a spark plug cap.
- Move the lead away from the spark plug.
LET THE ENGINE BECOME COOL BEFORE YOU REMOVE THE SPARK PLUG.
The muffler stays hot after use. A hot muffler can burn your skin.
- Let the engine become cool.2mReport a problem with step 3, Isolate the mower
- Toro warns that the muffler is very hot after the engine runs.
- The spark plug is in the hot part of the engine.
Remove the used spark plug
Estimated 3 min to 7 min
REMOVE THE DIRT NEAR THE SPARK PLUG BEFORE YOU REMOVE THE PLUG.
Dirt that falls into the engine causes wear.
- Remove the dirt near the spark plug.2mReport a problem with step 1, Remove the used spark plug
- Briggs & Stratton gives this action before the plug comes out.
- Use a clean cloth or a small brush.
DO NOT PULL THE STARTER ROPE WHILE THE SPARK PLUG IS OUT OF THE ENGINE.
The blade turns and can cut your hand.
- Remove the spark plug with a spark plug socket.2mReport a problem with step 2, Remove the used spark plug
- Turn the socket counterclockwise.
- A different socket can break the porcelain.
- Put the used spark plug on a clean surface.<1mReport a problem with step 3, Remove the used spark plug
- Do not let dirt fall into the hole in the engine.
Examine the used spark plug
Estimated 3 min
DO NOT CLEAN A SPARK PLUG WITH A SHOT BLASTER OR WITH ABRASIVES.
Briggs & Stratton refuses this method. Abrasive material can go into the engine and cause wear.
- Examine the porcelain of the used spark plug.<1mReport a problem with step 1, Examine the used spark plug
- Briggs & Stratton names a crack in the porcelain as a reason to replace the plug.
- Examine the two electrodes of the used spark plug.<1mReport a problem with step 2, Examine the used spark plug
- Briggs & Stratton names a burn on the electrodes as a reason to replace the plug.
- Examine the used spark plug for deposits.<1mReport a problem with step 3, Examine the used spark plug
- Briggs & Stratton names very stubborn deposits as a reason to replace the plug.
- A deposit on the electrodes stops the spark.
- Discard the used spark plug.<1mReport a problem with step 4, Examine the used spark plug
- Keep the used plug until the engine runs correctly again.
Set the gap on the new spark plug
Estimated 4 min to 9 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Compare the new spark plug with the used spark plug.1mReport a problem with step 1, Set the gap on the new spark plug
- The thread diameter must be the same.
- The thread length must be the same.
- Speak to a dealer if the two plugs are different.
- Measure the gap with a spark plug gauge.2mReport a problem with step 2, Set the gap on the new spark plug
- The gauge gives the distance between the two electrodes.
- Briggs & Stratton tells you to use a gauge and not a rule.
DO NOT CHANGE THE GAP ON A PLATINUM OR IRIDIUM SPARK PLUG.
The thin electrode breaks easily.
- Set the gap to the value from your documentation.2mReport a problem with step 3, Set the gap on the new spark plug
- Briggs & Stratton tells you to bend the curved electrode gently.
- The gauge touches both electrodes lightly when the gap is correct.
Install the new spark plug
Estimated 2 min to 4 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Install the new spark plug by hand.1mReport a problem with step 1, Install the new spark plug
- Turn the plug clockwise with your fingers.
- Your fingers protect the threads in the engine.
- Stop if the plug does not turn easily.
TIGHTEN THE SPARK PLUG TO THE TORQUE THAT YOUR DOCUMENTATION GIVES.
Too much torque can damage the threads in the engine.
- Tighten the spark plug with a torque wrench.1mReport a problem with step 2, Install the new spark plug
- Use the torque value from your documentation.
- Toro gives a torque wrench for this action.
- Connect the lead to the spark plug.<1mReport a problem with step 3, Install the new spark plug
- Push the lead onto the spark plug until it is tight.
Record the work
Estimated 2 min to 4 min
Source: 22in Recycler Lawn Mower — Operator's Manual · tier 1 · accessed 2026-07-29
Source: How to Change a Spark Plug · tier 1 · accessed 2026-07-29
- Start the engine.1mReport a problem with step 1, Record the work
- Stay away from the muffler while the engine runs.
- Speak to a service dealer if the engine does not start.
- Write the date and the hours of use in your records.<1mReport a problem with step 2, Record the work
- The interval for a spark plug is in hours of use.
- A calendar month is not the same as an hour of use.
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- spark plug
- Also called: sparkplug, spark plugs, mower plug, lawn mower plug, lawnmower spark plug, the plug
- spark plug lead
- Also called: spark plug wire, plug wire, spark plug cap, spark plug boot, ignition lead, the rubber cap on the plug
- spark plug gap
- Also called: plug gap, electrode gap, gapping the plug, spark gap, how far apart the prongs are
- spark plug socket
- Also called: plug socket, spark plug wrench, plug spanner, the deep socket with the rubber in it
- electrode
- Also called: the metal tip, the hook on the end of the plug, the prong, the little bent bit
When to use a professional
Stop if the new spark plug does not turn easily by hand. Damaged threads in the engine need a repair. Speak to a service dealer.
Stop if the used spark plug is wet with oil. Engine oil on the electrodes is a sign of a different fault. A service dealer must examine the engine.
Stop if you cannot find the gap or the torque for your engine. Do not use a value from a different engine. Speak to a service dealer for the correct values.
Stop if the engine does not start with a new spark plug. This page does not give an engine diagnosis. Speak to a service dealer.
Do not turn the mower onto its side for this work. You can reach the spark plug from above on a walk-behind mower. This page gives no method to turn a mower.
Do not remove the blade. This page ends at the spark plug.
Common questions
How do I change the spark plug on a lawn mower?
Disconnect the lead from the plug, let the engine cool, clean the dirt away from around the plug, then unscrew it with a spark plug socket. Look at the old plug, gap the new one to the figure your engine's documentation gives, screw it in by hand until it seats, tighten it to the torque your documentation gives, and push the lead back on. That is Briggs & Stratton's published sequence and Toro's operator manual agrees with it. The whole job is short. The reason this page is longer than the job is the two numbers in the middle of it, which are not ours to give you.
What gap should my lawn mower spark plug be set to?
The one your engine's own documentation gives, and this page will not print a figure. Briggs & Stratton says directly that your engine repair manual provides the proper gap for your engine, and that you should contact your local dealer for the correct specification if you do not have the manual. Its own reference charts split by engine family and in places by build date code, which is exactly why a single number would be wrong for somebody. Toro's operator manual for the 22in Recycler does not print a gap at all. A gap is a clearance, this site treats clearances as safety-critical, and a safety-critical number that we cannot trace to your engine is one we do not guess.
How tight should a lawn mower spark plug be?
Tight enough to seal and no tighter, at the torque figure your engine's documentation gives. Both Briggs & Stratton and Toro publish a figure for their own engines, and both frame it as a value for that engine rather than a value for all engines, so this page sends you to yours rather than reprinting one of theirs. Over-tightening is the common failure: the cylinder head on a small engine is soft, and stripped threads there turn a five-dollar job into an engine repair. Toro's manual tells you to use a torque wrench, which is the only way to know you hit the figure rather than guessed it. If your documentation gives no torque figure, ask a service dealer rather than working from a number you found for a different engine.
How often should I change a lawn mower spark plug?
Toro's maintenance schedule for the 22in Recycler says replace the spark plug every 100 hours. Briggs & Stratton recommends changing spark plugs every 100 hours or every season across outdoor power equipment engines, and its service FAQ says to do the check annually and in line with your operator's manual. Those two agree, which is worth noting because they are separate manufacturers. Both are counted in engine hours rather than calendar months, which is why the last step of this page is to write the hours down. Briggs also names a machine that will not start as a reason to look at the plug straight away, rather than waiting for the interval.
Can I clean a spark plug instead of replacing it?
Sometimes, and Briggs & Stratton publishes how: a wire brush or a spray-on cleaner made for the part, and a sturdy knife to scrape off tough deposits. It is emphatic about one thing you must never do, which is clean a plug with a shot blaster or abrasives. But it also lists three conditions where cleaning is not the answer and the plug is finished: cracked porcelain, electrodes burned away, and very stubborn deposits. Given a plug costs a few dollars and the job is the same either way, replacement is usually the better call, which is why this page is written as a replacement.
My lawn mower will not start. Is it the spark plug?
It might be, and Briggs & Stratton names a machine that will not start as one of the two triggers for servicing the plug, alongside the annual interval. So it is a sensible and cheap first thing to look at. It is not the only cause of a no-start though, and this page is a replacement procedure rather than a diagnosis. If the engine still will not start with a known-good new plug correctly gapped and tightened, stop and speak to a service dealer. Chasing it further usually costs more than the visit.
Do I really have to take the spark plug wire off first?
Yes, and it is striking how many manufacturers open with that same instruction. Toro says disconnect the spark-plug wire before any maintenance procedure. Briggs & Stratton makes disconnecting the lead the first action of the spark plug service itself. Murray says the same before you inspect or remove a blade, and Honda says to disconnect the spark plug cap before you tilt a mower. A small engine needs no key and no battery to fire, and the blade turns with the crankshaft, so the five seconds this takes is the whole of your protection.
Is a lawn mower spark plug the same as a car spark plug?
No, and swapping in something that happens to thread in is a real way to damage an engine. Briggs & Stratton warns that although several different spark plugs may screw into the engine, using the incorrect one will result in performance problems and possible internal engine damage. Reach, heat range and thread size all have to match what the engine was designed around. Buy the plug your engine's documentation names, or give a dealer the engine model number and let them look it up.
Related procedures
- How to find and record the model and serial number of every appliance in the house
- How to clean or change the air filter on a lawn mower
- How to grease the gearbox on a string trimmer or hedge trimmer
- Level a riding mower deck side to side and front to rear on flat ground
- What size blade fits my mower, and how do I check the length, center hole and mounting pattern before I buy a replacement?
- How to change the blade on a lawn edger
- How do I set a click type torque wrench and what setting do I leave it on when I put it away
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1How do I check, clean and change small engine spark plugs?
- Tier 1How to Change a Spark Plug
- Tier 1What is the right spark plug and gap for my small engine?
- Tier 122in Recycler Lawn Mower — Operator's Manual
- Tier 1How is the blade from my walk behind lawnmower removed?
- Tier 1Lawn Mower Maintenance & Support
Revision history
Current version 1 · updated 2026-07-29 · next review due 2027-07-29
- v1 · 2026-07-29First draft. Sourced to three Briggs & Stratton support documents, the Toro 22in Recycler operator's manual, Murray's walk-behind support FAQ and Honda's lawn mower maintenance page. NO SAFETY-CRITICAL VALUE IS PUBLISHED AS A NUMBER. The spark plug gap, the installation torque and the plug part number are all per engine model and all three publish as consult-the-manufacturer instructions with verified false; Briggs & Stratton's own statement that the engine repair manual carries the gap is what the page rests that refusal on. The three verified specifications are replacement and service intervals, which are not in config.json safety_critical_specs. They carry no spec_key because data/specs.json is written centrally after the merge; the registry entries should be added there. Two source ids, briggs-changing-spark-plugs and briggs-identifying-the-correct-spark-plug-and-gap, are proposed in data/sources-additions-replace-a-mower-spark-plug.json and are not yet in data/sources.json, so the record holds on check 3 until scripts/sources_admit.py admits them. The procedure keeps the mower upright throughout: tilting a walk-behind mower is what defers check-mower-blade-condition under the Phase 1 screen, and the spark plug does not need it.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.