http://img253.imageshack.us/img253/1829/blockzw5.jpg

What are these holes for, specifically the small one which seem to go very deep. I've been trying to fix an oil leak for months now that seems to be coming from that area, just wondering if they should be blocked. I have oil coming from what looks like that area on both sides of the block, just pouring out, of course despite spending months of staring at it, I can't figure out exactly where its coming from.

Those holes go nowhere, I can only guess what GM put them there for. (brackets/wire looms/etc)

Oil leaks in that area are most likely from the end seal of the intake, but I have also seen head gaskets where the "ends" didn't extend to the edge of the intake surface, great area for oil to leak at a suprizing rate. Could also be coming from the sending unit behind the intake.

Just a thought, but if you have a plastic line for an oil pressure gauge or even a copper one they can crank, and will puke tons of oil... Keep us posted..../

It seems to be running down both sides, my oil pressure line is offset to just one. I'm getting sick of working on this, months and months, i'm thinking I'm just gonna spray baby powder all over the area in a last ditch effort to find out where its coming from. Messy but I'd rather have a messy engine bay than a useless car.

Sprayed powder all over the drivers side of the back of the block and went for a drive to get expensive fuel. Came back and there was a nice define line coming down straight from the oil pressure hole. I'm going to powder the passenger side see if anything is leaking over there. Meanwhile I'm trying to think of a definate way to fix that leak so I can make it to the track event I paid for tommorow. Thanks.

In the 1957 era the spark plug wire loom bolted there. One hole threaded and one is to index the bracket

I just got back from the track, I didn't manage to fix my leak aparently. Oil spray all under the hood. The road track sure beat on my car, my clutch doesn't seem right anymore and my rear brakes couldn't handle the pressure and both are bleeding. Also, bench seats don't work well taking turns at high speeds. :o I survived though and so did the chevelle. Still no idea about the leak, I'm guessing its just intake manifold again. 4th time the charm? I'm getting sick of redoing it.

Is there some trick to doing the rear gasket with rtv, I put the intake straight down don't move it around, I put a nice thick bead, lots in the corners. Everytime it leaks.

I chased a bunch of leaks on my 350 before pulling it in March. Not only did the valve covers, pan and timing cover gaskets leak, but the rear of the intake leaked and there was a pinhole in the oil pan that the po had epoxied over and painted. It spotted the driveway everytime it was run.

Sometimes if the pcv is not working right, it will "enhance" oil leaks out of places like the rear of the intake/head seal, too.

Sorry, I originally meant to say, that having tried both methods several times, I have gone back to cork intake end gaskets attached with Hi Tack gasket cement and a dab of silicone at each end.

Get ALL the surfaces REALLY clean, with brake cleaner, etc. Lay the bead and let sit for 10 minutes. Drop the intake straight down and torque the bolts in the proper pattern then go in the house and don't go back out there for 24 hours. The rtv will cure and you'll have no leaks. I use the black RTV on the ends and Hi-tack on the side gaskets. Don't short cut it and fire it up early. I'm also assuming that you have a proper vent or PCV valve on the engine.

I have a hose from one of the valve covers to the carb, and the pcv valve rattels niceley so it can't be stuck. I never have leaks at the front of the engine, nor vaccum or coolant leaks on the gaskets, just the rear for some reason always leaks, I've had two different intakes and both leaked so it can't be the intake. I always wait 24 hours before start up. My only guess is that it hasn't been clean enough, I always clean surfaces with rubbing alky before but I'll try brake cleaner next time.

http://img253.imageshack.us/img253/1829/blockzw5.jpg

What are these holes for, specifically the small one which seem to go very deep. I've been trying to fix an oil leak for months now that seems to be coming from that area, just wondering if they should be blocked. I have oil coming from what looks like that area on both sides of the block, just pouring out, of course despite spending months of staring at it, I can't figure out exactly where its coming from.
Going up from your circle there is a plug in the block that is partly covered by the head. I've had a leak there and that plug is under pressure from the oil pump. After replaceing intake gaskets twice I found it.

Before you tackle that job again you should completely clean the area and run the engine while watching it closely so you get an idea as to where it's coming from. If it's seeping around the oil fitting threads the intake doesn't have to come off. I haven't seen a leak at the crossover plug that pizzi's talking about (will be mostly underneath the driver's side head) but if it was removed for cleaning and not properly sealed/tightened that could certainly be the problem. I would get the engine completely up to temp. (20 min drive should do) Clean the area off, (don't start yourself on fire) start the engine and watch for leaks. Then you'll know what to fix.

The block has never been taken apart for cleaning, it was a crate motor and I changed the heads from GM to Edelbrock. I know its leaking from up top because I can see the oil. I put baby powder all over the back of the block went for a 15min drive and came back and this is what I saw. Below should be a simple drawing of the engine from an overhead view.

http://img523.imageshack.us/img523/196/leakbasicma4.png

The orange is oil, the red is the dizzy, the little brown dot is my oil pressure fitting that goes into a nylon line to my mechanical guage. As you can see there is oil all over the back of the block between the intake/heads and bellhousing (not shown in picture).

I found my leak after cleaning block real good and then using a mirror so I could see better. Try a mirror from your wifes/ girlfriends/sister compact