Spark Plug Blew out threads on Head

[nicklow241]

I recently bought a beat up ATV for beating around the yard / lake. Its a 86' KLF 300 which is a four stroke. Anyway i spent about 350 fixing it all up (new valves, piston, guides, ect.) Get it all together and run it for maybe 3 hours tops. well last night the spark plug flew out of the head taking the threads and all. im guessing the previous owner had stirpped it slightly before and re tapped it causeing it to hit the exhaust valve which is why i had to rebuild the top end. Anyway.

What options do i have in fixxing this problem.

Could I drill a bigger hole tap it and put in those thread fixers.

Is it possible to weld in more material and re tap.

I just dont want to claim this as a total lost of time and money. THANKS

 

[Rcannon]

I believe I would look for something else to be wrong. Sure, the stripped plug could be a random thing, but maybe something else is wrong in the engine.

 

[biglou]

I would think there are several options. If you took the head to a machine shop, they could install a heli-coil or timesert, or possibly build the area up and re-tap the threads. I think the "landing" where the spark plug rests is what will determine how far into the head the plug protrudes. Be sure the plug size is correct, and that this landing isn't lowered any, letting the plug drop too far into the cylinder. I doubt this is the problem, however, as re-tapping the hole wouldn't have changed the height of this surface. I'm also reasonabley sure it wouldn't have run for a few hours before smacking the plug if there were interference to begin with.

All this is just a semi-educated guess, however!

 

[nicklow241]

well i know the spark plug is correct. I know it wast hitting any think internaly there was just barely any threads to hold on to. I called a Local machine shop they want to weld the hole in and retap. but they havent seen it yet. im going to go pull the head right now. take some pictures and post them

Thanks for the help

 

[Rcannon]

I remember someone posting in this forum one time. It said that spark plugs generally do not come loose. Look for something else.

Two weeks later we were riding. A younger friend on his CR 80 had his bike stop at the bottom of a jump. We looked at it and noticed a very loose spark plug. Obviusly, we tigten it and move on.

Two laps later the bike stops . The engine refused to turn over. The piston had shattered. Had we heeded the warning, we could have avoided a pain in the butt job of cleaning the lower end.