Damaged Spark Plug Threads

[Huddart33]

Has anyone successfully repaired damaged Spark Plug Threads in a Grob 2500-E1 Cylinder Heads,

I am not a favour of Helicoils in Air Cooled heads.

The cause of the damaged threads seems to be the Spark Plugs protruding too far into the cylinder.

The last few threads get corroded and damaged the threads in the Cylinder Head when removed

some months later. Ours it fitted with Bosch WC7D, I am not sure if the original Bosch WB240ERT1

reach was different. The recommended Champion REN30S have the same reach. 

An Austrailan Gliding Club was recommending putting two copper washers to reduce the amount 

of protrusion into the cylinder. None of this seems satisfactory.

[xintersecty]

Interesting, when we pulled spark plug one and the bottom threads looked corroded.  It looked like this pic I stole from amazon.  My mechanic and I thought they were old looking.  My engine was rebuilt about 40 hours ago and they used the original plugs.   So it sounds like the corrosion was so bad when you pulled the plug it damanged the threads.  😞 

 

 

[philphil_99]

I believe you could get a thread chaser from an automotive supply store or potentially aircraft spruce. You could also repair the damage threads on the plug with a thread file. Most damage is  caused by Carbon on the lower one or two threads. This could be fixed by adding another washer raising the plug so they don't get the same carbon buildup.