ORIGINAL: Ernie Misner
Best thing I ever did was get a 1/4x32 die for cleaning up new plugs before installing. Apparently the plug's threads are just rolled and not precision cut from the factory. You would be amazed at all the shaving that come off of new plugs to make them right.
Ernie Misner
Actually the shavings coming off the plugs are most likely making them fit much worse in the head.
The worst case scenario is that after chasing them the plugs now seal at the copper washer under their head rather than at the first thread.
Not a good idea at all, and really the reason that bottom sealing plugs like the Turbo and the Nelson give about a 1000 rpm advantage over the stock standard threaded ones.
Yours will be much worse!.