Put my pistons back in the block with new rings and conrod bearings and couldnt crank it over (by hand)
Took them all back out to check the rings and their all fine
Put piston 1 back in (closest to belt) and tightened it up and the crank is locked again, loosened it and it spun freely, tightened back up and locked again?

Any ideas? bearings oiled up, new ones looked identical to old ones etc