Well im sorry that youve problems already, and i hope that this is your worst setback! .. but i have to ask you whether you have already decided what you are prepared to do. you say that you do not want to helicoil.. why is that? Is that because you do not want to remove the engine? I guess you have to decide whether you are only prepared to accept a solution which involves leaving the engine in situ ..
I was the Engineer on a Research Ship for some years and in that situation the parameters for problem solving were clear..everything(including ideas!) that existed within the hull.
If your own parameters include removal of the engine then i can tell you that when i had the same problem happen to an crankcase that i was working on, i bored out the badly corroded hole and loctited a sleeve tapped with the thread (1/8 bsp i think) Maybe people have got round this by fitting 1/4 bsp fitting but there doesent look to be much meat left if you did that. Personally i think helicoil sounds like a great idea.. If youve got or can get a 1/8 BSP helicoil..you wouldnt even need to drill it..you could just tap it straight..
If you glue it (and although araldite is great it is a little brittle and my father long ago expressed a preference for super epoxy because it retains a greater amount of flexibility), it wont be as good versatile or robust as a mechanical repair (of course you know that!) but it might well work for a long time. If however it does get knocked and leaks, I would imagine that the combustion chamber would rather pull air than oil..that being the main possible danger.
Just to add that for all the precision engineering of my fathers race bike.. It still has a chunk of the left hand combustion chamber glued in with super epoxy and some bandage after a capscrew was inhaled through the transfer and was punched out by the big end.. That happened a year and a half ago and although it also lost the bottom of the piston in the event , it was racing again that afternoon. The pistons of course have been replaced..but the hole epoxied with bandage hasnt been touched..
so if you did it right of course it could be fine.
good luck with establishing your parameters. Its thirsty work!
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