Pack the drill bit n tap with grease. Then after tapped rinse out by running a couple gallons of kerosine throught it then leave drain open for about a day to air out. Did it to my first engine worked great can't think of a better way.
I had to re-tap and put in a helicoil on my friends LTR oil tank covered the drill bit with grease and the tap with grease. then poured the old oil threw the motor to flush out the shavings worked fine after that.
Hay man I did the exact same thing. take your plug to the auto parts store. get somthing as close to that size as you can. It will have to be just a little bigger because you got to cut new threads. It will probbly be standard and not metric. but thats ok. But what you do is get the tap that you need(it cuts the new threads) it is a tee handle device. put it in striped out hole and start turning vey slowly. it will cut new threads. now when that is finshed dont plug it up yet and pour diseal fuel through it (YES TRUST ME DISEAL FUEL) that will flush the shavings out. do that several times. catch it in something so you can see what you are flushing out. then pour some cheap thin oil through it. put your new plug back in fill with oil let idle for 10 15 min drain oil change filter. put in new oil and filter and your ready. ANy questions call me 828-467-1172 I fixed mine and my friends. this happens on these quads. dont use universal plug it wont work dont use heil coil. cut new threads. VERY VERY SIMPLE
I went to Pep Boys they sell the drill bit, tap and helicoil all in one package. If you use a helicoil just put some RTV on the helicoil thread and then install it this will guarantee that it will not leak and once your done just use the stock bolt. Make sure you get your stock bolt size and thread pitch.
I know this is old thread but I recently got kfx450 and when changing oil I found out small bolt threads were stripped.
I drilled and tapped for M8-1.25 and got flanged 10 mm long bolt at Advance Auto parts store.
One thing to watch for is they machined seat for the washer and material around it is higher. Now M8 washer won't fit the "seat" and smaller washer won't fit M8 bolt. Also, new bolt flange is wider than the "seat" and when tightened it won't seal well.
I solved this by buying copper washer that fits machined seat and drilling it to fit the bolt. That did it.
I torque to 11 ft-lb and it works great - no more leaks....