I have a 1972 Malibu that I put a 502 boat motor in. The motor runs good but the bell housing has almost cracked in two. I have raced it pretty hard a couple of times. I have solid motor mounts and either a solid tranny mount or rubber mount. I have been told the reason it is cracking is because I was using a 3200 stall instead of a 4000 and that it was the way the boat motor was designed. I ve seen big block chevelles pushing more power than me and never have the problem I have, and they dont even have a cage. I am just needing a little more insite on what the problem could be and would appreciate any help anybody can be.

is it Aluminum or steel?

It is Aluminum

Maybe dirt or grit between the engine block & the bell housing before they where bolted together?? Dave