Ade,
I was told all it takes to build an engine is the willingness to fill a 55 gallon drum with botched parts. I have seen silver solder used with success with steel, but a quick search on google had puddle in the results. Have you considered Loctite? Have seen it hold fine in a pinch if fits are tight, but maybe a kludge too far with your nice work so far.
Len.