Oil draining wet sump & flow inside crank case

Hello,
I have a '74 850. I am interested in some detail about the oil flow, routing inside the crank case. The Old Britts red/blue diagram is very good but i am not following whats going on in the crank case. Does the oil pump inside the timing case handle the return to the oil tank as well as the feed to the engine? If the need arises to drain oil due to wet-sumping, is it better to drain by pulling the large sump filter body (A) or the smaller sump drain plug (B) or both? Is the channel (C) in the case a return? from where? I poked around but could not find a thread on this. If theres a good summary somewhere, just point me in the direction to find it. Thanks for any assistance you can offer.

The oil pump is in two sections, the forward section pressures up the engine, while the larger rear section scavenges the sump and returns oil to the tank. The scavenge section is larger to ensure the pump can return more oil to the tank, than the pressure part can deliver to the engine.

When changing oil, removing the large plug will completely drain the sump. To relieve a wet sump condition, removing the smaller plug will suffice.

I think (think means not absolutely sure) the channel C is part of the top end lubrication oil return. Oil drains from the rocker boxes thru a hole on the timing side, then thru a corresponding hole in the cylinder barrels, then turns horizontally into channel C.

Slick

texasSlick said:

I think (think means not absolutely sure) the channel C is part of the top end lubrication oil return. Oil drains from the rocker boxes thru a hole on the timing side, then thru a corresponding hole in the cylinder barrels, then turns horizontally into channel C.

Click to expand...

Rocker box drains to the timing chest, last photo:

The cavity 'C' is the timing chest drain.