I went to change the plugs and air filter on my 2011 Raider with ~48,000kms on it yesterday and everything was going smoothly until that dreaded rear right plug. The old plug came out fine but the new one would get about 2 turns by hand in and then bind. After much trial and failure with taking the new plug out, checking the angle/threads etc, I determined that the threads in the head had been damaged, perhaps when the dealership had performed my 25,000km service. My buddy (who is much more mechanically inclined than myself) came over and we determined we should try to clean up the threads with a tap. Fast forward to this morning and we tried tapping about half the threads in the head (with the threads looking much better than they had previously). I know that a reverse tap would have been a better idea as there are less chance of metal shavings getting in to the head, but we used a small hose and a shop vac to hopefully clean out whatever shavings had gotten in to the cylinder.
The new plug threads in further than before but we can't get it in fully, and we didn't want to force it and potentially damage the threads further. So, all that to say it looks like I may have to pull the head to have the hole tapped properly.
Has anyone had to do this and is pulling the head possible without removing the entire motor from the bike? It's likely something I'll have done at a shop because I have little desire (and even less time) to be able to do this type of work