Thanks to everyone for the posts, RT, I had thought about filling the HX with water to protect the inner tube joints during soldering but immersing it also should be even better, thanks. I will check the mounting and bonding
Diver Dave, I have always maintained a good pencil zinc in the HX, the article you posted is interesting if a little over my head, you would think this would be a more common problem if it were just a salt water corrosion problem
The faces on the casting that blew off look clean (once cleaned off with a wire brush) with no trace of solder, if they were tinned properly you would think that there would be some indication of the solder in the surface of the brass. I'm assuming that a lead/Tin solder is used rather than a Silver solder?
I've just sand blasted the casting and still no sign of solder, see pics.
I am a little concerned that the soldered joint on the smaller internal tubes are being affected by the same phenomenon so i think I will have to bite the bullet and buy a new one (as cheap as I am!). I'm just wondering about the other engine HX now!
Thanks again Steve