Posted by James Hall 3 on 07/02/2022 15:26:56:
Nicholas Farr: Yes, I should have tried drilling it out but impatience got the better of me, I'm afraid.
I'd wondered about a piece of trapped swarf, but 'galled up' is a new one on me – could you educate me here please.
Galling James is when two pieces of similar metal rub against each other as in fitting together. It can happen when you least expect it and is rapid occurance and virtually immoveable. Aluminium is probably the worst, followed by mild steel and then brass – though I have only worked with stainless on rare occasion I believe it too is also likely to gall.
It is very unlikely that steel would gall on cast, nor cast on cast but if you do manage to get the parts apart there will be a distinct witness of where the galling occurred.
When I built the Atomatic engine the aluminium cylinder head galled on the crankcase – despite gingerly trying the thread on I felt it 'go' and no amount of trying would reverse it. The case was held in the lathe and could not be moved so the head had to be machined off and remade, the galling just one small spot in the thread which had to be re-cut.
Hope that explains it for you
Tug
Edited By Ramon Wilson on 07/02/2022 18:06:07