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jimcanoe

spark plug blew out

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jimcanoe
While running just fine the spark plug blew out of the cylinder head ruining the threads in the head. What would cause this to happen and should I just get a new cylinder head? Thanks, Jim

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MowerMechanic
if it is a flat head then yes your easiest option is a new head. You can Helicoil but dont plan on it lasting. The only time i had this happen to me is when i put a machined down high compression head on my kohler 10 hp with an ethanol fuel mix and advanced the timing:O. My bet with yours is someone prior had cross threaded the plug when it was changed.

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dentwizz
Actually if it is done precisely a Helicoil can be quite durable. Aircraft engines with aluminum heads actually come pre-helicoiled because they last longer. It is super critical that you get the hole drilled exactly to the right size.

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Al
Hi, We put heli-coils in all the time. They are more durable than aluminum if installed properly. People tend to over tighten spark plugs. This damages the threads. Tighten the plug finger tight plus 1/4 turn. Josh is correct, items that are built to mil specs, do not have bolts screwed into aluminum threads. Either heli-coils or other thread inserts or captive nuts are used. Worked on this stuff for Rockwell International for 38 years. Al Eden Al Eden

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