Here’s how to replace the spark plug on a Honda CB125E or GLH125SH.
To do this you will require:
- Spark plug wrench from toolkit, 16mm deep socket or 5/8″ deep socket
- Spark plug gap tool
The spark plug – just one on this motor – sits on the right hand side of the engine amidst the engine fins:
It’s hidden underneath the spark plug cap:
You can lift the cap off with minimal pressure:
Place the cap and lead somewhere where they won’t be bent or crushed. Now you can see the top of the spark plug:
If you don’t have the spark plug wrench that comes as part of the bike’s toolkit, a 5/8 deep socket or 16mm deep socket work to remove it, though given it’s easy access you can probably manage it with a wrench as well.
It’s easily removed with a ratchet:
Mostly undone:
You can assess the condition of the fuel/air mixture by examining the end of the spark plug (an article for another day):
Also examine the condition of the center and side electrodes. If there is obvious damage or the edges are eroded, replace it – they’re not particularly expensive items and there’s no good reason to use a damaged plug. This is also a good time to check the spark plug gap (another article).
Grab the plug that’s going back in – new or old and OK. If re-using the old plug, make sure that the crush washer is present and undamaged. When reinstalling a spark plug, thread it in by hand to begin with to ensure you don’t cross-thread it. If you meet resistance, back it out and start over.
Once it bottoms out by hand, you will have to turn a new spark plug more than an old one to get it to seat – effectively crushing the crush washer. For a new plug, ighten the plug 1/2 a turn after it seats, then back it off slightly so it’s loose then tighten 1/8 of a turn.
For an old plug, simply tighten 1/8 of a turn after it seats.
Reinstall the spark plug cap:
…and you’re good to go!