Originally Posted by
JohnDThompson
I was wondering that myself. I suspect the one-piece headlug/head tube frames are probably more susceptible to this type of failure. You'd have to remove the fork and look into the head to determine this: a one-piece head tube will have large openings in which the down and top tubes are visible. The three piece head tubes will only have small vent holes in the head tube to allow the down and top tubes to vent and drain properly.
Certainly looks like the original Nikko Italian cut long point head lug to me. If an 80-81 it would be that. Same with 82 but shorter point. (?) One-piece came later and were shaped differently. The relief of the "lug" against the head tube would be shallower than against the down tube. They look the same in the photo.