How to Change a Sparkplug on a CBR 125 Motorcycle

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Changing plugs on a motorcycle is good yearly maintenance. It's easy enough to do yourself, follow along with your owner's manual and these steps and pictures.

Steps

1. 1
   Gather your tools. You'll need the tool kit that came with the bike, and probably the manual to follow along with. You need your new spark plug CR8E (NGK) or U24ESR-N (DENSO). It costs about US$8.
   
   

   
   
2. 2
   

   Look at your new plug.
   Look at your new plug. By the manual you should have a gap that is 0.70-0.80mm (0.028-0.031 in).
   • 

     You check this with something called a feeler gauge that looks like this picture.
     You check this with something called a feeler gauge that looks like this picture. This tool is just a pocketknife full of different thicknesses of metal. The 'gap measurement' is the number stamped on the feeler blade that will fit between the plug's electrodes without being forced.
3. 3
   

   Prop up your bike and get to work.
   Prop up your bike and get to work.
   • 

     For guaranteed safety, you could disconnect the battery first.
     For guaranteed safety, you could disconnect the battery first. First locate the plug. You don't have to remove any parts of the faring (plastic body) to get at it. The plug has a connector wire on it that might be kind of hard to remove by hand. Treat things gently, you can use the small pliers in your toolkit to slowly and deliberately lift the wire straight off the plug.
4. 4
   

   Keeping clean.
   Keeping clean. Clean around the plug and where it fits with the engine. Digging around here with a toothbrush is fine, maybe you have a real garage with compressed air? The point is to keep crud from falling to the inside of your engine -that would be bad.
5. 5
   

   Tools.
   Tools. You have a spark plug tool, really just a crude socket. You will turn this with the '17' half of your wrench. If you've misplaced the original tools, the plug could be removed by a long socket, or some clever wrench that is 5/8.
   
   
6. 6
   

   Remove old plug.
   Remove old plug. It's pretty close quarters in here.
7. 7
   

   Now you have a motorcycle with a hole in it.
   Now you have a motorcycle with a hole in it. Again, this is a bit like open heart surgery. Nothing goes in here but the new plug.
   
   
8. 8
   

   Quick comparison.
   Quick comparison. Old vs New. In this case we probably could have got away with scraping the old plug clean. But the plug is 2 years old already.
9. 9
   

   Place the new plug in.
   Place the new plug in. FIRST screw the new plug in by hand until its firmly seated. Don't force anything, cross threading on the engine block itself would be horrible. Honda is pretty particular about tightening with the spark plug tool: New NGK Plug directions:
   
   A) Tighten a 1/2 turn after plug seats.
   
   B) Loosen the plug.
   
   C) Now tighten plug again: 1/8 of a turn after it seats.
   
   
10. 10
    Replace the spark plug wire. This went back on a lot easier than it came off.
11. 11
    Done. It's pretty satisfying to do simple things with a bike yourself. This is simple enough that it can become an annual maintenance thing. A motorcycle should be a great way to learn more about mechanics. You don't need to have ramps, jacks, or a lift. Assuming you also have a car, if you fumble bike maintenance then you still have a ride in to work the next morning. Keep your mind and wrenches turning.

Warnings

• Inspect the Plug! The 'gap' between the two electrodes must be a certain width, or you risk damaging the bike. (Or it just might not work at all)

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