This 1977 engine shovelhead engine has the oil purging problem.
I've worked on the oil pump. The ball seat looked questionable, and the bypass valve plunger was hard to get out of its' bore (on the verge of being stuck, I think). I whacked the pump housing on a block of wood til I got the plunger out.
I glass beaded the whole assembly, and when I reassembled it, the relieve valve plunger would glide up and down in its' bore. I put the pump housing in the bridgeport and touched up the seat with a drill bit ( took a real light cut, barely took off any metal[sm=innoc.gif]) and put the ball back in and hit it with a brass drift in hopes of reseating it. Might not have hit it hard enough? Engine is carrying at idle 10 psi pressure and higher rpm 20 to 30 psi.
So, is that ball check valve supposed to keep oil from seeping down from the oil tank into the crankcase? Is it just letting what oil remains in the return hose going to the tank seep back down into the sump? Sure more than a hose full from the looks of it. Probably more along the lines of 2 or 3 shot glasses full.
I could try to reseat the ball again, I suppose.
Another question. This oil is coming out of a hose from a fitting below and to the left of the oil pump position. I take it this is a crankcase breather port.
Well, there is another line coming off of the crankcase above and to the left of the pump housing, but it is plumbed into the oil tank. Is this a crankcase breather, too.
Is the little steel line from the crankcase to the bottom of the rear cylinder rocker cover feeding oil to the rockers? What feeds the front set of rockers?
Does oil drain down the pushrod covers back into the crankcase? After I replaced the oil pump and started the engine, I started to get oil welling up from the rear cylinders' tappet guide assembly, oozing up around the pushrod cover base. I know there is a cork gasket down there. Is that oil draining down from above and not getting back into the case, or is it welling up from the hydraulic lifters for some reason? Enlighten me[sm=ttiwwp.gif]
I will check back for replies and maybe answer questions you may ask.

Good possibility the check valve seat is toast. I won't say you might've screwed it up with the drill bit routine, but .... You might try to get a new ball, touch a welding rod to it, and use it with valve lapping compound to make a new seat. The valve is s'posed to keep the oil in the tank and outta the bottom end of the motor when it ain't runnin'.

If it ain't seatin' and you are wet-sumping, it'll puke out the breather line as you describe. The other line you mention is the oil tank vent.

The small metal line from the crankcase going to the rear rocker box feeds oil to the top end. It gets to the front rocker box via another small line between the rocker boxes. After the oil lubes the rockers and valve stems, it drains through internal lines to provide additional lube to the rings, cylinder walls, pistons, and main bearings. The oil from the rocker boxes also drains down the pushrod covers and lubes the tappets, tappet guides, tappet rollers, and pushrods. It then dumps into the crankcase sump and is scavenged by the oil pump.

The cork gaskets are known to start leaking after awhile, especially if they are older and start getting hard.

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