Been reading posts on this on the boards about this. Decided to share here, however I think comments and tips should be posted to the correct board. I am not the only MINI owner that has had this happen.
David.

I had a 15% pulley and Alta cold intake done in 2005. Was advised to install colder plugs, so my tuner put in the IK22. These were in for 35-45k miles. Took in for oil, fluid service in 2008. Plugs changed to new IK22's. Oct. 2009, took off from a red light near work(after a 8 mile commute from home on the freeway). Heard a BANG, sucking sounds and all dash lites on. Was able to reinstall the plug (number 1), and drive home. Next am I re torqued all plugs to 21ft/lbs. Checked plugs every month (about 2k mi.). #1 seemed to always require about a 1/4 to 1/2 turn to torque to 21. All other plugs fine. June 1 I check the plugs. #1 just turns and will not tighten up. All other plugs fine. Take #2 plug and try to insert into #1 cyl. Just turns. Ordered a TimeSert and 2 inserts the next day. Called dealer and asked what the OEM plugs were. Was informed that they were NGK BKR6EQUP. Dealer quoted $24.99 ea. Called auto parts store, quoted $6.99 ea. My neighbor and I spent about an hour last Sunday, cut new threads, cut new seat, installed the TimeSert insert. Installed the NGK's watched as my neighbor's (Ford & Chevy guys) cringe as I torque the plugs down. So far, 125 miles on this repair, still a little gun-shy on full throttle except getting on the freeway, but so far so good. Gas mileage seems to have improved also. Total cost $220.00. Now the next question, Do I keep the MINI for another year (as I had planned) or trade now? BTW 78k miles on odo. __________________

 

Thanks for this. I've got an Alta 15% pulley, and Alta CAI to install for my 2005 Cooper S. From this and others that I have read, I will be getting the 'colder' plugs, new belt, and possibly a tune when this is all done.