Very unusual spark plug failure.

[frank rabbets]

My hedge cutter started to make a rattling noise. I thought disaster was on it's way so continued so as to get full life out of the machine. When the machine cut out I started to investigate and found the insulator had come loose and was chattering up and down. The 2 pictures show the extent of the movement.

 

[Chris]

Frank I had exactly the same on my chain saw Took me ages to work it out.

 

[Shayne]

Not a new problem because i remember seeing that nearly 30 years ago in a 2-stroke bike , fortunately a quick find because to clean the spark plug with sandpaper was my first thought .

 

[clivehorridge]

Never seen that happen Frank, seen plenty where the electrode has burned away, but not a loose insulator...

every day a school day ...

 

[frank rabbets]

My brother had a misfire which took him ages to find. The lower part of the insulator had snapped and when in position slid down the central electrode thereby shielding the spark gap. On checking the plug one held it up the other way and the broken part slid into place thereby looking OK. Best to hold plugs in their working position to check but I've only seen one such failure.