[Z1R rider]

I always take the head off if I strip sparkplug threads (on various motors), some say it can be done with head on without getting drilling metal in the motor but I've found most times there isn't enough room to drill and tap with the head on, and you don't wonder how much metal fell into the cylinder. I don't even get a new head gasket unless it's bad, I paint it with copper or aluminum paint and put it together before the paint dries, I've yet to get a leaker doing this. (all surfaces cleaned well) I always take the head to a machine shop to have it repaired, never done the do it yourself kits.

and always put anti seize on the plug threads when you have an aluminum head!!!