changed my wifes 2010 sportster plugs today--front came right out, reaer one was a bear--once out i could see why--looks like the threads are welded together. this is the first time i changed these plugs (2 yrs). I took the 'good" old one put a little anti-seiz eand worked in in and out of the hole, and then installed new one--torqued to spec. But what would cause this...

 

Looks like aluminum siezed to the steel threads. You are lucky there are enough threads left to hold the plug without a helicoil. Probably caused by no anti seize and over tightening.

 

No anti seize and over tight.

 

I don't think he was too lucky. Those welded on areas probably took out the rest of the head's threads as they were backed out. I think it's helicoil time.

 

Actually it probably took out the top 2 threads and worked half way down the plug as it was removed. I would chase it with a tap (12mm I believe ). Just use anti seize next time.

 

I guess a flashlight and mirror might help to see what damage was done.

A word to the wise. Remove your plugs now and apply some anti-seize to the threads! Same goes for your cars and trucks with aluminum heads. With spark plugs designed to last for years, and aluminum heads replacing cast iron heads, the welding of spark plugs to aluminum heads is pretty common.

 

I appreciate everyone's feedback. It did look like the top few threads were messed up, and the new one (with anti-seize) tightened up to spec. i will chase it with a tap. i have changed my dyna's plugs several times over the past 2 years, i guess i need to pay a bit more attention to the sportster

 

I would be very carefull using a tap, metal shavings are likely to go into the engine. May not want to run a tap thru?

 

You put a tissue in the hole and put wheel bearing greese on the tap to prevent shavings from getting in the cyl. Finish with pulling the tissue out and blowing out the cyl. Or find a good aluminum magnet!

 

Good to know, thx