I am not familiar with the "Clinton" or what engine is in it.
About that pinky sized hole; when it runs does exhaust come out of it? I would think not because with a hole on the head you could not get compression and the engine would not run.
There is a possibility that there is supposed to be a compression relaese valve there and for some reason it is now missing.
Can you post some photos of the bike and of the engine and particularly of the "hole" area?