Spark plug rethread size.

I was replacing my spark plugs for the first time the other day when I quickly realized that my #2 cylinder spark plug hole is stripped. I am looking at my options for re-threading the hole (Time-Serts) but my main problem is figuring out what size the re-thread kit needs to be. Does anybody know what size a KZ650 spark plug hole is? I think it is a 14mm X 1.25 but I could be wrong. If anybody can help out i would really appreciate it. Thanks!

It is definitely 14mm... I don't buy Timeserts because of the cost of their plug kit but buy the NAPA inserts which are solid (not a wound wire). They are much less espensive. You also have to take into account the length of the insert as you don't want it down in the combustion chamber. They have 1/2" and 1" (as my poor old memory tells me but it is suspect). That being the case, I generally buy the longer and cut it to length as I would NOT install an insert without removing the cylinder head. All you have to do to remove the head is remove the nuts atop the studs and use a new gasket. I know it seems like a chore to remove the head and lots of folks will tell you about using grease on your tap but the head is aluminum and while you might get MOST of the shavings from tapping for the insert, I never felt good about getting them all. If you don't remove the head, you could probably fabricate a straw type attachment for your shop vac and suck out most of what falls on the piston. I would leave the piston at TDC where the work is to be done. If I didn't remove the head, I would use the 1/2" long insert as well.

George, thanks so much for the info. Thanks for the lead on the inexpensive NAPA insert. Timeserts are painfully expensive for a one-time-use product. There is one product that I came across that claims to rethread without having to pull the heads because the tool will rethread from the bottom going up. The tool is called a "Back-Tap". HERE I spotted a post you made a while back saying that you have never had good results with any rethreader and that inserts are the way to go. I am not the most mechanically inclined person in the world so if I can use the rethreader to fix the problem without pulling the head then I think I will try that first. If it doesn't work then I am not out anything and will go with the insert route.

I totally understand when you said to make sure that the piston needs to be TDC. One question though - how can I ensure that the piston is in fact TDC?

Oh I thought you would find this interesting. When I was researching the topic of using inserts - I ran across a unique idea someone had come up with when tapping a head while th head was still on the bike. A guy said he got the piston at TDC and used shaving cream to fill the chamber to keep the metal shavings from falling into the well. He then simply vacuumed the small shavings that were "floating" on top of the shaving cream at the base of the threads. Pretty ingenious.