Personally I think it's a none starter, it may well resist the heat, it'll be protected by the plug after all, think the trouble you'll have is trying to cut a new thread, there simply won't be enough surface area for it to bond too and resist the cutting action of the tap.

Can't believe there isn't a local machine shop that couldn't fit a helicoil for you, it really is the proper way to do it tbh.......

Could be. If it doesn't work a thread insert will be just as available as it ever was.

If tapping doesn't work, casting threads around a suitable greased bolt (if I can get one) might be an option, though might end up plugging the hole permanently.

Aftermarket heads are allegedly 100US. Normally this would be unbelievable, but there was a Charade clone big in China, so maybe just possible. Unfortunately the engine number is on the head, probably precluding a swap in Taiwan.

There may well be machine shops that would do an insert, but I dont know them, and might not trust them if I did. Certainly DIYing it seems to have many screwup possibilities, notably the free hand drilling.

Re it being "the prop[er way to do it", aside from, tbh, not giving a tinkers damn about the "proper" way to do anything, I'd say it was analagous to doing a dental implant without trying a filling first. Would seem rather improper behaviour in a dentist.

Literalising that analogy, I wonder how dental amalgam would do in this sort of application? Probably rather hard for a lay punter to source, but would be quite interesting to test it. Mysterious stuff..

..

You haven't yet told us what you intend to do about the scored cylinder liner yet, think that could be a bigger problem to solve, have you found oversize pistons and rings and a full gasket set?

Re the scored cylinder {which I dont think is quite accurate. "pitted" would be closer) I'm probably not going to do anything.

It wasnt using a lot of oil or noticably down on compression before this unfortunate series of events, so unless the damage is very recent, which I have no particular reason to believe, it wasnt apparently having much functional impact.

Assuming there isn't an invisible crack or perforation due to cavitation damage in the water jacket (which it does rather resemble) it might be OK on reassembly.

I doubt the "proper" rebore you imply by your list of bits is a realistic option.

Long time ago I had a clutch slave cylinder fail on my 1800 Marina. While I was kangarooing home without a clutch I broke a piston ring, which scored the bore and ring land and put quite a lot of dents on the piston crown (which fortunately was partly protected by deposits from leaded petrol)

I replaced the broken ring and clutch slave cylinder, gave it a decoke, re-ground the valves, and put it back together. No new head gasket, or anything else.

Worked fine until a rotted spring hanger bracket got it, maybe a year or two later.

Edited by edlithgow on 13/05/2023 at 07:58