I was always told not to do it either. I don't know the longevity of expansion/contraction over a long period because I changed motors in that car more than I changed my underwear.
The exhaust manifold that I welded lasted for quite a while until I saved up enough for hedders and new exhaust.
If you have ever dealt with a small block 400 you know how the heads crack easily between the steam holes and the head bolts. I remember finding a crack in each head. I couldn't afford to replace them of have them fixed professionally. I just ground a 'v' along the crack and gave it a good tack, ground it down and never found any antifreeze in the oil. I guess when you don't know any better you'll try anything.
Do you know why you're not supposed to weld cast? I too have heard not to weld it, but no one seems to know why or what happens.
This has been probably 10-15 years ago. Actually, there are a lot of things I used to do back then that I wouldn't do today
Gone are the days of duct tape & coat hangers!
