Big threaded hole under transmission

[Mountainmaam]

I feel stupid for asking, but I'm curious about this hole, it is dead center and oon the trans. About an inch and half in diameter, and there's no cap. I can see gears inside!? Doesn't that need a cap of some sort?

[fo4imtippin]

Usually a barring hole. So you can put a star shaped bit and turn the engine over to get to top dead center, etc. It should just be the flywheel under there which doesn't need to be sealed.

[cadillackid]

in fsact you typically dont want to seal it.. if you should get an engine oil leak or a trans fluid leak you want it to drip out and not fill that area up. sometimes there is a loosely fit piece of metal over it just to keep excessive dirt and water out.. but many trucks dont even have that.