What is the purpose of this plug and o-ring?

[bryancraftyhands]

I discovered I had been seeping oil very slowly for some time. So slowly I never would have noticed by checking levels. The give away was the discolored spot formed under my bike that should have weathered away if it had been left over from the last time I changed oil in that spot and spilled some pulling the plug. I traced it to this spot.





I thought it was a crank seal plug, but when I pulled it to replace the o-ring, I see nothing there. Is this just seriously a hole with an o-ring and a plug just to have something to have to replace? There is a twin on the other side.

 

[Gary in NJ]

I believe that is an oil pressure port. The plug is removed to screw in a test gauge.

Do the threads measure at M16 (around 5/8")? If that is it, it gets tightened to 8 Nm (5.8ft-lbs or 70 in-lbs)

 

[bryancraftyhands]

If I remove it again or the other, I would measure them. To reach the one I did that was leaking, I had to remove my coolant hoses from the water pump. I may end up doing this before the end of the summer as my coolant came out looking like yellow. I know I filled it with green a couple years ago.
The other side wasn't leaking so I have not touched it. It has easy access though. As far as torque goes, it takes an 8mm allen key and I'm hoping I didn't already strip something putting it back in with just my hand and allen key. I'm going to watch it for that leak and if I see it, I'm probably going to have to do something to get it to hold better.
As far as for oil pressure gauge readings as a possible use, I don't see it connecting to any thing.
In a parts breakdown it is listed as
line item 20
Plug, Straight Screw
90340-32004-00
in the crankcase cover 1 assembly section.