I have the engine fully split and i bought a new left case to replace mine.
I *think* this came out of the replacement case but i’m not certain.
For the life of me I cannot find where the hell this piece+spring go.

Anyone recognise it??
www.imgur.com/jIUTJz3

Shift drum detent pin and spring. Goes in from bottom of engine and held in by what looks like a drain plug.

THANK YOU! Appreciate the help. My headache is already big enough doing my first full engine rebuild.

Just keep asking questions, you’ll get it done.

Don't fit that until the cases are together or it won't go together [or there'll be damage if you force it]. Just goes in after & runs against the selector drum to hold it at the point of 'totally in gear'--in each gear. Ignore this if already been said.

Thank you for adding this, i probably would have done exactly that.

So i am assuming that since this thing fits in that “not a drain plug” plug, that I can just simply remove that plug and put it in there after the case is sealed?

If that came out of the replacement case then in theory you should have two of those there somewhere. If it was brand new out of the box case then it won't have that, or the bung screwed in. But if second hand then its quite possible i suppose. Just be careful & you'll be good. As you now realise, with the gearbox out of the case, that item can fall out inwards, if that makes sense, but is fitted from the outside under that cap after cases bolted up. Cheers.