That's... a new one

[Anticept]

I'm tracing out an ignition system issue on one of our aircraft. Never seen this happen before.

 

 

 

 

 

To be quite honest, I was lucky to find this. I was poking the spark plug with my ohmmeter to make sure they were correct (they should be around 3-5k ohms). I touched the ceramic barrel and saw it move...

 

My gapping tool is this style. This allows me, without touching the center electrode or ceramic at all, to move the ground electrode. The only pressure on the center is from the sliding of the feeler gauges, that's it.

 

CSIR report sent!

 

EDIT: I just found another one like this??? I'm pulling all of them to check. This is odd. I replace the plugs every 200 hours, and these are about 150.

 

EDIT 2: I found four of them like this out of the 8. I'm going to keep a close eye on things in the future to see what might be causing this. I just double checked with my gapper tool and the tooth doesn't come anywhere near the ceramic while gapping...

[Anticept]

I think I know the cause. Made a video about it:

 

 

I had a helper gap these broken plugs last time. It's possible he may have broken them on accident. I really really had to try hard to get it to break with the tool I'm using, so I'm not so sure he did or didn't break them, but I still wanted to share a video demo.

[Anticept]

At first, none. As time went on, the mag check had a growing spread. After about 40 hobbs hours it failed with a spread of over 450 rpm @ 4000.

 

Rotax took interest in the issue and I just sent in my final report. I was waiting for junk plugs to test this on. Seems plausible that this was the cause!

[Mike Koerner]

Thanks for showing us this Corey. It looks like its closing the gap that is the problem. Maybe we should just push the outer electrode down against a bench instead of using the tool.

Mike Koerner

[Anticept]

You can use the tool to close it by grabbing the top. I've always done it that way. This video is to stress how important it is to not touch the insulator and demonstrates one way that it could be damaged.

I had to really try hard to get it to break, and very deliberately use the tool incorrectly.

[Tom Baker]

I tap mine down by holding it in one hand and using a flat tool to tap with. I then check with a feeler gage. When I am in rhythm I can get the gap right almost every time. 

[Runtoeat]

I've done it Tom's way and have also used the anvil surface of my vice for tapping the electrode on.  I usually tap gently and try to sneak up on the correct gap so I don't need to pry it open with the gap tool which is part of my feeler gage and same as Corey shows.  Never felt good about prying the electrode - suspected it wasn't good for the plug.

[Anticept]

The plugs' ground electrodes are designed to be opened and closed, and you aren't moving them by much.

[Mike Koerner]

OK. I've got several ways to try next time. Thanks guys.

Mike Koerner