383 knock goes away on warmup

I talked myself into building a hotter 318 in my truck because of a knock just to find a cracked flex plate when swapping the two engines. It needed replacing anyway, is what I told my wife.
yep, in my early years i rebuilt the heads on the 318 in my challenger to cure a misfire. then i fitted a new distributor cap and rotor arm to actually 'fix' the problem :lol:
neil.