While I understand the theory behind the reservations of using a Time-sert due to dissimilar metals, in practice I've never seen a problem--and I've seena few plugs come out of Time-sert hole. The burn pattern is always similar to the other plugs. Besides, if one really cared about it they could use an aluminum Time-sert insert (but I just don't think it's necessary).Yes you can thread another helicoil into a hole thats had one back out. As for time-sert its not a good idea to make a bigger hole in your head and insert a steel threaded plug into an aluminum head. different growth rates for the metals will cause fautigue and leakage. If you question if the helicoil will come out go to the local auto parts store and get a rethread kit, and just be preped for the worse case. If you dont need it take it back.