Help diagnosing oil leak(s) and troubleshooting

[SkidmoreGarage]

I have a 67 with the original 327 (with rear crank vent tube and sealed valve covers), and it is a leaky mess that is only unliveable when it's running. It leaks from the rear (through the bell housing weep hole), the front (the front crank seal), the sides (valve covers), and the bottom (pan seal). I replaced the valve cover seals and resealed the intake, and those appear to not be leaking as much, but the total amount seems to be the same.

This has been happening for a long time based on the amount of oil and dirt caked under the truck and on the engine (1" thick in some areas). When its parked it forms hanging drips but is generally not that bad. I put a drip pan under it. However, when it runs, in about 10 minutes of idling, it's enough to have streaks running down the front cross member, and puddles on the ground.

Now to the point, I think I have a crankcase pressure problem, but I wanted to check with those who have more experience. Does this sound accurate? Do the rear vent tubes get clogged? Is there any improvements or ways to test for excess pressure in these old 327s? Or, is it common and I just need to start replacing seals?

[kwmech]

Check the back of the intake where the oil line come into the block-- or the back of the intake itself

[geezer#99]

Your rear crank tube (road draft tube) doesn’t work to pull fumes out until you’re moving. Likely near 20 mph.
What do you have on your oil fill tube at the front of the intake?
Does it have a cap or a breather.

[SkidmoreGarage]

Thanks for the replies. I don't have a draft tube but rather a vent that goes to the bottom of the air filter. I have an oil cap, not a vent.

[geezer#99]

You need to connect that vent up with an inline pcv that’s plugged into manifold vacuum on your carb or intake.
And you need a vented cap.
Nice pics in post #4 for what you need.
What carb you got?



http://67-72chevytrucks.com/vboard/s...d.php?t=645971

[jimijam00]

Definitely need a pcv and breather but that won't solve the hemmoraging you have going on. I'd do a gasket and seal R&R. Maybe a top end refresh, a bump stick, smoothing out the intake, and a new h20 pump just for giggles.

[Jcfcamaro]

I'm going to guess and say maybe its coming from the rear main seal <crankshaft>. I built a real nice 350 for my Camaro several years ago and fought a similar leak and being a 4spd car you can't have oil in that area very long without more problems. Had guys tell me it could be rear main seal or oil galley plugs leaking. Ended up pulling the transmission and cleaning everything off so I would be able to see it leak fresh oil,then started it up and watched it. Ended up being the rear main. But leaks are hard to find...Good luck...

[ohboy321]

Does your intake manifold have a breather/filler tube on the front? The 327 with the internal ventilator and the port off the rear of the block would have had a vent tube like the pic below.

My truck had no functional PCV when I purchased it. The rear port was blocked off and someone at some point had stuffed it with foam. The internal ventilator was also missing. As a temporary fix I tried using a valve cover PCV but results were not that great. I am in the process of correcting this now.

[SkidmoreGarage]

Thanks everyone for the replies. After a bit of diagnosing, I think the issue is that the truck was originally a California truck and came with AIR injection. I think it was a removed by a previous owner and the valve covers were replaced with non-vented 327/275HP covers, leaving only the rear breather tube open. I am hoping adding some vented valve covers and pcv system will reduce the oil pushing through the seals. I'll also pull the intake to verify the rear breather oil separator isn't clogged.