We Have Spark!

It’s been an arduous week and a bit! I’ve spent hours upon hours overhauling the ignition system on the CT125. I inspected and adjusted every single part of the system to bring it as close to factory specification.

Late last week I managed to get the spark plug to spark when grounded against the engine casing. The celebrations were limited however as I found the spark to be occurring no more than one in three times I kicked the motor over… It didn’t take long before I tracked down what seemed to be the issue. The camshaft seemed to be rotating as expected when cranking, however the spark advancer assembly seemed to only rotate a little and cease rotating with the camshaft when trying to push the points ignition shoe. Without knowing more about the points system and spark advancer assemblies, I could only assume something was missing that should otherwise be holding the spark advancer in place on the end of the camshaft.

To the workshop manuals I went… My first port of call was to dig up exploded parts diagrams for related assemblies:

CT125 Points / Spark Advancer Assembly Diagram

CT125 Camshaft Diagram

It became apparent that the parts designated by “11” and “14” on the first diagram were missing when looking at my points and spark advancer assembly:

CT125 Points / Spark Advancer

Fortunately for me, I have not one, but two other Honda 125cc motors in my workshop, so I was able to source the necessary parts from another:

CT125 Camshaft w/Bolt

CT125 Camshaft

I promptly removed the bolt (the main missing part) from the end of the spare camshaft and went to test fit it in the camshaft of the CT125 I was working on. To my dismay and confusion, the bolt didn’t seem to fit at all, and seemed too thin and long for the job. I thought to myself what could be going wrong and thought perhaps alternate camshafts were shipped with different revisions of the Honda 125 motor, so I returned to my desk and began investigating to see if this was the case or not. Oddly enough, I was unable to find any mention of a camshaft for the Honda 125 that had a different section where the spark advancer sits. Something didn’t seem right! I took a further look at the end of the camshaft on the CT125 and the answer soon revealed itself… The previous owner had twisted and broken the existing bolt in the hole so there was no head present to show that a bolt had once existed there.

Broken Bolt In Camshaft

This was going to be damn tricky. I proceeded with a screw extraction strategy that I’ve been honing in the past month across a range of applications.

The bolt I extracted was properly rooted!

Replacement Bolt vs. Broken Bolt

Replacement Bolt

With the nuisance of a bolt extracted, I cleaned and reassembled the points portion of the motor again.

Now that everything is back where it should be, I’ve tested kicking the motor over… The spark is big, blue and reliable! The operation looks to have been a raging success. Time to focus on the next issue – the fuel system.

Thanks for reading!