What's this bit?

[fredintoon]

XS11SG.
I have the alternator cover removed.
At the bottom (6 o'clock on the flange) of the cover there is a thumb-size pocket that opens to atmosphere with a shiny steel patch at it's bottom.
Sticking out of the crankcase there is a steel pin mebbe 3/16" diameter that looks like it would press against the steel patch in the cover. The pin flares out to a mebbe 3/4" diameter as it enters the crankcase casting. It feels a little loose but I don't want to yank on it until I find out what it does.
Help?
Fred Hill, S'toon.

[xssiveone]

Fred, I would have to check the manual to be 100% on this, but I believe that plug closes off one end of the main oil passage. The other side has a threaded bolt/plug, but this side just has this plug sitting in place, held in by the cover.