I stripped the hole on my 1999 xr100 what size helicoil do I need or can I drill and tap it to the next size? If I can what size drill bit, what tap, what size spark plug will work?

 

Your best bet, is to helicoil it. They work very well and you dont have to worry about them pulling out or not holding.
Just make sure the chips from drilling and tapping dont go into the motor.

 

how do i know what size to use

 

If you go here,
ngk number breakdown
Youll see for a cr7hsa plug the threads are 10 mm. And the h shows a 12.7 mm reach, which is 1/2 inch. So youll need a 10mm by 1/2 reach helicoil. If you buy the thread repair kit, the proper tap and insert, and installation tool, are included.
If you look at this chart,
chart it says no drill required for a spark plug repair, just thread the tap in, with some heavy grease, to catch the chips. Go a little at a time, and clean the grease and chips off of the tap as you go.
Heres an article on helicoiling.
helicoil how to

The little bit of searching i did, i didnt see any good prices. I was expecting to see, somewhere around 40 bucks for the kit, and the going price i found was about 100 bucks.
You might want to try and shop around, maybe ebay, and find a better price. I believe the correct tap is 10mmX1mm sti (sti stands for steel threaded insert). But double check the spark plug, the lead, or thread to thread distance should be 1mm, or about .04". Thats the second number of the tap.

 

thanks alot

 

Check Ace Hardware too. They sell some kits for rethreading spark plug holes. They also sell an epoxy resin for repairing spark plug holes. You mix it up, put it on your plug, then insert the plug. Wait 5 minutes then remove the plug. Let is sit for another few hours to finish hardening. If you tried this and it worked, great. If not, you could still go the other route.


/Jon