How to Change a Lawn Mower Spark Plug

Spark plug and spark plug wrench.

What You’ll Need

To change the spark plug on your lawn mower, you will need the following.

1. Spark Plug

Lots of hardware stores sell spark plugs for lawn mowers, as well as agricultural supply stores, auto parts stores, home improvement centers, and lawn mower repair shops. If you bought your lawn mower at a big box store, check there first – they often carry parts for their stock lawn mowers.

To find the correct spark plug, consult your lawn mower owner’s manual. Or, take the old spark plug with you to the store, along with the make and model of your lawn mower. Most parts stores have a reference book where you can look up the part number and compare it with your old one.

2. Spark Plug Wrench

This handy tool makes changing your spark plug a snap. Or, I should say NOT a snap, because the purpose of the tool is to help prevent the ceramic plug body from breaking! Special spark plug sockets are also available for standard socket wrench sets.

3. Spark Plug Gap Gauge

This inexpensive small gauge is used to measure the gap in the spark plug where the spark is generated. If not adjusted correctly for the plug and mower, the spark plug will not spark. Check your lawn mower manual to find the correct distance.

16 COMMENTS

  1. Following your instructions, I changed my mower’s sparkplug. (Good, clear instructions!) It started easily and ran normally. The next time I needed to mow, it wouldn’t start and sounded like it did before changing the spark plug. Thinking I might have made a mistake with the plug, I replaced it with a new one. It started right up and ran normally. Couple of weeks later, same story. I have now used 4 plugs this season. Am I doing something that causes the plugs to have shorter lives? Thanks!

  2. The article on changing spark plugs was excellent– it was clear, easy to follow, easy to understand. Most important, it took the fear of attempting to do a mechanical repair away! I have compleat confidence I will be able to to other maintenance jobs as well to start up my riding lawn mower in a properly maintained manner. I purchased it last year with 11 hours on it, but want to make sure it is in good shape before I start up. Thanks for the great articles Jackie Shepard.

  3. response to judy S.
    Judy S. Says:
    July 23rd, 2011 at 7:03 pm
    Following your instructions, I changed my mower’s sparkplug. (Good, clear instructions!) It started easily and ran normally. The next time I needed to mow, it wouldn’t start and sounded like it did before changing the spark plug. Thinking I might have made a mistake with the plug, I replaced it with a new one. It started right up and ran normally. Couple of weeks later, same story. I have now used 4 plugs this season. Am I doing something that causes the plugs to have shorter lives? Thanks!
    =====
    hi judy. i think you have a problem with step 5…tightening the spark plug. most plugs need to be tightened very snugly and it is hard to do with a small tool like in the pictures here. i recommend one quarter to almost one half turn after it is contacted the motor and is very finger tight. now is the time to use a wrench to turn it the extra quarter turn i previously mentioned. of course if it was stuck on some rust and not yet fully seated it will turn more til it is very tight and does not allow the combustion gases to escape which makes your mower not start or run horrible. good luck 🙂

  4. Hi! My husband bought a new mower, put in the oil and gas, then started it but it didn’t start. He then realized it had no spark plug in it. He went out and bought the right one, put it in, and it still won’t start. Is it ruined? Any suggestions?

    • Rebecca,
      That shouldn’t have damaged the mower. Make sure you have the right plug for the mower, and the spark gap is set to the correct distance.

  5. I have a powerforce mower and for the life of me, I can’t find the spark plug!!! Do you know whereabouts on the mower it is? Had the hood off and can’t see it.

  6. I changed the spark plug on my old mower without problem, but now I have a mower I bought last summer and it has a very long snug boot that I can’t get off my spark plug. Needle nose pliers get no grip at all on the boot and the boot is so deep that I can’t get my fingers or a screwdriver to the end of it to pull it off. How can I get to my spark plug???

  7. First time trying to do this. There was inadequate warning about the tightening of the spark plug,and I tightened it too much, and wrecked the pin thingy on end of plug!!

  8. I took my lawnmower out today for the first time this season. I put new gas in and checked the oil, but still it didn’t start. I took out me booklet on the lawnmower and it said to change the spark plug. I know where it is and how to get to it, but how long do they last? I had it checked out last year where I purchased it and they said they did it. How short of life does one spark plug have??? Thanks Lots

  9. I can change my spark plug easily but even though the plug is tightened, it pops out when I start my mower. I confirmed the spark plug is the correct size/number per manufacturer instructions. I tried the old one and the new one, they all pop out when I start the mower. Can the housing thread be stripped and if so, how do I fix that?

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