bear with me this is going to take some explaining, my motor that i have in the machine shop right now to have the head trued and ported and polished is all set to go back together and the guy called and said there was at least one stripped head bolt in the block, at firt he said it shouldnt be a big deal that i needed a threaded insert called a heli coil to usse the original bolt, however there is no insert offered on a 9mm x 1.25 metric bolt. So he said he could drill it out and tap it, BUT he was worried if he opened up the head to allow a bigger bolt that he may rupture into a water jacket and the head would be ruined so in a nust shell has anyone had to open up the bolt holes in there head to allow a bigger bolt or is there any thing i can do that anyone knows of? im out my bike until i figure something out ahhhhhhhhh please help someone, if it makes any difference its the second piston on the exhaust side that has the stripped bolt

 

this might sound dumb,
but could you go 1 up from metric to a slightly bigger standard?