Hello hope everyone s ok , could I have some input please ! I have a cylinder head & it’s currently has two plugs in which seem to have been there for a long time  I’m scared to remove them & strip threads I’ve been soaking in penetrating oil for a week has anyone any tips heat ? Brute force ? Any advice appreciated thanks again 
 

stripping the threads unlikely
have you put a spark plug socket and some torque on it?

Not at the present !think I will get some penetrating oil (‘plus gas ) & soak some more then try it seems a trivial but I really don’t want to do any damage through being impatient thanks for reply appreciated


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I was using wd 40 to soak but not penatrating oil apparently


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Must be me but i always think how the hell can oil get in past a thread done up tight. I recon it has to be cracked a bit first to let even the best penetrating oil get in. Bolt the head down to something & swing on the socket. If the plug breaks--its not my fault--is it--Umm. Ok if ya crack it free then use penetrating fluid, soak & work it back & forth. If the thread comes out well--hellicoil job.

I do not claim to be an expert, but I have been working on small to large engines since I was 14 and I am not almost 57 and have NEVER stripped head threads loosening a tight spark plug.  I think you should put a sparkplug socket on it and apply torque necessary to crack it lose.  If you find it stripped its because that's how it was put together.

just my opinion

I can understand the reluctance.  Some car engines are allegedly prone to having plug corrode into the aluminum head and threads coming out with plug.  Plus not all plugs have the nickel plating on the threads like NGK and corrode much worse. 

Pulled threads seems to happen with high mileage and no maintenance.  If you're really worried, pop the head off, invert it, and use your penetrating oil in the combustion chamber.  On the Fords that had this issue, the recommendation was to slightly loosen the plug and then apply penetrating oil...  but they were conical seat plugs and not gasketed if I remember correctly. 

P.S.  I've never had a problem with a Yamaha...  even ones with original plugs that look to have been in place for decades...  but you can see what you have and we can't... 

Thanks for the reply’s & input I will give it a go later on thanks again


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Job done ! Guess I was being over cautious thanks again


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"Job done ! Guess I was being over cautious thanks again"

Well done.

No problem with being cautious and asking questions. Measure twice, cut once and all that!