I just rebuilt my bike.  Not a fan of aluminum threads and mine had some damage from yrs of use. While it was down I decided to install Heli-coil steel spark plug inserts. The instructions said use high temp RTV to seal them. I'm thinking it should be hardening Forma-gasket or thread lock, Despite my better judgment I did it according to the instructions. It is to set up for at least 24hr before use. Because of work mine sat up for over a week. Rode it around for a few days put a few hrs on the clock. took out 2 of the 4 plugs to look to see how it was running and 1 insert came out leaving an RTV mess in my head. I cleaned it out and reinstalled it with thread lock, but I'm thinking maybe should have used forma-gasket. Thoughts?

I'm rebuilding a shovelhead after not messing with one for over 20 years. I've lost a good deal of my memory so I'm basically trying to remember things as I go. Why install steel heli-coil when the aluminum around the steel is going to expand faster and 2.5 times more? Makes heat transfer suck too. I'd go with the aluminum heli-coil but really, I've never had to do that spark plug insert so I'm just throwing what I know out there. Good luck. Still, why the steel heli-coil....FWIW

if you notice your cylinders have steel inserts for torqueing the heads. spark plugs are steel so steel on steel is better. I've used heli-coils on many other things and always used thread lock to secure an insert, this is the first time, I know of, heli-coil said to use RTV instead of thread lock. kinda disappointed I went by the instructions instead of instinct. These actually say for aluminum heads. Maybe the expansion is the reason for RTV but I've used inserts in other aluminum parts before with locktite and never a problem I've never seen aluminum heli-coils through out the years I've seen lots of issues with spark plugs stripping aluminum heads not just HD but bikes and cars

First off I have never seen aluminum helicoils that are bigger than a number 14 screw. I used the blue RTV thread lock that I use on everything. I was told that once I changed the inserts and properly torqued the plugs in place with the blue rtv that you were not supposed to mess with them at all for at least 1000 miles. Maybe this gives the insert some time to corrode/lock itself into place? Not sure but I still have the bike and now the plugs come out no problem.