Hi guys. I would like to know what Is the function of this hole located in the head of the last rear cylinder? Thank you.

 

When the head is mounted to the engine block. If i recall, you use that plugged hole to insert a rod down in to find "TDC" Top Dead Center of the piston...
Don't know why they used the number 6 cylinder instead of the number one cylinder? But guess it doesn't matter... result should turn out the same...

 

Thank you very much!