Clamshell won’t close

[Bud Man]

Dropped the engine in my ‘29 yesterday and all well. So this morning decided to button up the u-joint housing and no go. New felts installed, lightly greased, but if I try to attach the clamshell it’s a no go - doesn’t want to close. Engine sitting correctly on its mountd so wondering what’s happened. Anybody out there experienced this? One solved, she’s ready to fire! Appreciate any input from more experienced Model A folks.

Bud