Can you get any movement at the crank? If not, something in the main bearings are locked up. May even want to look at the clutch, you never know. If it move just a little then I would presume something in the rods or a siezed piston would be at fault.
Good luck tracking it down,
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!