I am working on trying to repair my cylinder head as the threads vanished when it shot up the spark plug. Does anyone know the right size of the thread hole?

 

If you are doing it yourself I would say you could helicoil it, but that depends on how much of the head came out with the threads. Measure the hole and then you can go to a local parts store and find the right one for you.

If you don't think that you have the tools or the ability take it to a machine shop and they can fix it by using a helicoil or welding back metal and the re-threading it.

 

Is this some common issue? Seems like my plugs are working themselves lose and now I have this same issue with the cylinder head. Not a cheap repair.

 

I believe the spark plug threads are M14x1.25, good luck, sounds like a nightmare.

This is the first time I've heard of it, But you never know, people remove spark plugs a lot on these cars and if you over-torque aluminum while its warm, it's never a good day.

 

You always should swap plugs with the engine cold and always tighten the plug a tiny bit before backing it all the way out of the head. I like to tighten loosen tighten loosen tighten loosen a decent amount of times before I take the old plug all the way out. Way back in the day when I was a teenager I was changing out the spark plugs on my Ford Thunderbird Turbo coupe when the engine was hot. Well short story long got to the last plug and the threads came right out of the head with the plug. That was a lesson I learned early in life luckily and now I also use a decent amount of antiseize anytime I do my plugs. Btw back then I had to just take it to a mechanic and he helicoiled the hole and it worked great after that until I sold the car.

 

Makes me wonder if helicoil is a good option for the heat and pressures demanded by our little race cars...