I have been starting to do a total rebuild on a 1967 merc 650 (4cyl)This motor was running when I took it apart but it had a bad bottom shaft seal and bearing. It was sucking air and maybe water in around the bottom seal.
In the water jacket area there was a lot of clogging in the smaller water passages,
Anyway after cleaning everything very well, I noticed in the exhaust "chest" area, near the middle exhaust port for #2 and #3 cyl's
a small hairline crack in the aluminum going from just near the port about an inch downward to the piston skirt area of the cylinder.The steel cylinder liner does not appear to be cracked in either case and the crack is not in the water jacket area anywhere.Is this thing junk beacuse of this crack or is it insignificant? I can not see how it would leak any water or compression.
Thanks for any opinions.