Stumbled onto a free 73 Southwind jet, with a seized 455. I replaced the motor with another used Olds. First time in the water, Grenade, hydraulic #8, pounded the piston unrecognizable and sent the rod into the intake valley. Hmmmmm ? Retired the Southwind. Bought a 74 miller jet and had a blast running the BBC on the river. Took it home and after some cosmetic refurbishing went back to Lost Lake, put it in the water and 10 min later, Grenade , # 8, piston pounded to a pulp, camshaft broken in pieces, rod punched a hole in the cylinder wall. What the hell am i doing wrong?!