I bought a non running 1991 bayou 4x4 a few weeks ago and i go to turn it over for the first time and i could hear and feel air leaking out from around the spark plug. I took it out to inspect the threads and they are stripped but not completely gone. I can screw in the spark plug but when it bottoms out it just keeps turning and does not get tight. I took the head off because i planned on installing a heli-coil. The problem is, i think the plug hole is too close to the valve seats (pictures below) and if i use the helicoil tap to cut the larger threads it will remove material from around the valves and ill ruin the head.
Another issue i found is if i put my fingers on the top of the piston at top dead center i can rock it back and forth ever so slightly, not far enough for the piston skirt to contact the cylinder though. The cylinder itself is still smooth without any scratches but i cant see any crosshatch left. Do i need a new top end or is this common for an older machine? it has no hour meter and ive never seen it run so i dont know if it burns oil, but the oil level in the sightglass is just fine so i have no reason to believe it does.

Im more concerned about the spark plug hole how do yall think i should go about fixing it?

This is only the second quad ive worked on and the first time ive ever pulled a head so any advice or suggestions is appreciated
Thank you for reading

 

Now you have the head off, take the cylinder of too, remove the top piston ring and put it in the cylinder about 1/2" down from the top, measure the ring gap with feeler gauges. If it is over about 0.025" you need new rings, but check, or get checked, cylinder and piston for wear. Limits for both are listed in the workshop manual. If the cylinder is over limits, a rebore and oversize piston is required. There is no practical alternative to a Hellicoil for the spark plug hole, it is scrap if you don't fix it. I think the tap is only 1mm bigger than the cleaned up hole, so 0.5mm of wall taken away.

 

Is there any sort of sealant or epoxy i should use on the outside threads of the helicoil? im thinking JB weld just to insure there are no leaks

 

No the main seal is the washer on the plug and this will still seal with a Hellicoil fitted. Many two strokes and old B & S side valves seem to leak a little black oil from the plug to head joint, indicating the seal isn't perfect, so it does not need to be for everything to work fine..