76 Chevy 454 - massive oil leak in rear of engine

[MrDavidOgle]

I have a 1976 Chevy K20 4x4 with a 454 engine… I’ve got a massive oil leak at the back of my engine and replacing the rear main oil seal didn’t stop it! I’ve recently taken the top end off to give my heads a valve job. After it’s all back together and running quite well for about 8 hours or so (actual run time), it springs a massive oil leak at the rear of the engine, pouring down between the flywheel and the oil pan. It leaks a steady stream of oil when the engine is running (about the thickness of a number 2 pencil lead), and leaks nothing when it’s not running. Since I couldn’t prove to myself it was the oil pan gasket, I figured it was the rear main seal. So I removed the oil pan and the rear main cap and removed both pieces of the rear main seal. But they didn’t look damaged or give me any reason for me to believe that was the problem. I put it back together with a new seal, taking caution to follow the book so I didn’t get it in backwards. Unfortunately, I had to use a multiple piece oil pan gasket because that’s all I could buy. I made sure I had the rubber ends in the proper place and used a heavy bead of high temp red silicone on the corners, and a light bead on both sides of the rubber itself. It was a major pain in the *** to get the gasket to be where it belonged on the bottom of the timing chain, but I think I got it right. I used a light bead of high temp red silicone on the cork gaskets and put it back together. BUT IT STILL LEAKED JUST AS BAD AS BEFORE! Now I confess, I put too much torque on the oil pan bolts, and squished the pan gasket so I think I deserve a leak there and I could live with having to replace the oil pan gasket again… But what gives? Why the same massive oil leak? Maybe even a bit worse this time… I’ve been told that the oil pan isn’t under pressure, so it wouldn’t leak that much from the oil pan. A suggestion that I’ve heard is that I put the rear main seal in backwards, even though I think I didn’t. But the engine never leaked before I began my adventure into the top end and after replacing the rear main oil seal, it still leaks almost identically the same as it did before replacing the rear main oil seal. I was reading a thread on here and someone suggested that the distributor seal could leak oil. Is that a reality? Could that be my problem? Does anyone have any suggestions or ideas? Dave

[vanhal]

dave, could it be the cap that closes the end of the cam shaft ?? since you have changed the pan,crank, and top end gaskets just wondering ....pete

[MrDavidOgle]

I didn't know there was a cap that closes the end of the cam shaft... In the back of the engine, by the firewall? I never messed with it... Does this cap have a seal? Is it replaceable? I ran the engine successfully for a while after rebuilding the top end, so would this seal go out spontaneously, or could I have damaged it when I put the crank shaft back in??? I guess this means I need to take my engine out to see, huh? Should I leave my tranny connected to the engine when I take the engine out? Thanks for the reply! Dave

[vanhal]

Originally Posted by MrDavidOgle

I didn't know there was a cap that closes the end of the cam shaft... In the back of the engine, by the firewall? I never messed with it... Does this cap have a seal? Is it replaceable? I ran the engine successfully for a while after rebuilding the top end, so would this seal go out spontaneously, or could I have damaged it when I put the crank shaft back in??? I guess this means I need to take my engine out to see, huh? Should I leave my tranny connected to the engine when I take the engine out? Thanks for the reply! Dave

Dave it looks like a frost plug, if you know it is not the crank seal and the top end is ok then this could be it ..BUT .. it is under the bell housing so the trany has to be removed ..SORRY but that is what you have to do check with some other guys you know ok , hope this info may help ok

take care .......pete

[shopratles]

Dave, try this. Right below the intake manifold on the back of the engine, wipe any oil and gunk off with a rag. Start engine and let idle for a few minutes. See if oil is leaking from this area. Having experienced this before (I did it to myself) it sounds like you either forgot the intake rail gasket or it slipped on installation. If this is the problem, loosen intake bolts reinsert gasket and retighten. Good Luck.

[MrDavidOgle]

Whoa Cool! Both good suggestions! It's obvious I've never had this engine out huh!

VanHal, Where is the crank seal - in the back of the engine by the firewall? Perhaps this cam shaft cap (also in the back of the engine by the firewall) has an oil seal that could be leaking? I dont know for sure that the intake manifold isn't leaking as ShopRatles is proposing below...

ShopRatles, is the "intake rail gasket" - the rubber seal that goes on the back end (closes to firewall) of the intake manifold - between the block and the intake? Is this end of the intake manifod pressurised with oil? Would this much oil be able to leak at the rear of the intake manifold - obviously when under pressure when the engine is running? When I installed the rubber intake manifold gaskets, I put a light bead of red silicone on both sides of the rubber gasket and a heavy bead on both ends of the gasket filling any room for leak between the head gasket and this rubber intake gasket (I did the same thing on the front and back of the intake manifold gasket)... But, as you suggest, I cant be 100% positive that it didn't slip out of position during installation. The front doesnt leak oil!

But here's something to ponder... The oil is steadily dripping/gently pouring down (for lack of better terms) the rear hump on the back of the oil pan, but since the oil pan isn't under pressure it cant be the oil pan gasket itself. So it must be something above the oil pan gasket. If the oil was leaking from the crank cap, cam cap or intake manifold, wouldn't the oil be running off the side of the engine and/or bell housing? I dont think there's room between the engine and the bell housing or any way for that oil to get to the place its dripping from - is there?

Either sugguestion - I need to clean the back of the engine and find out if its leaking at the crank cap, cam cap or intake manifold. Its interesting how neither of you believe its the rear main seal leaking... I really appreciate your replies because it sounds like I was barking up the wrong tree!

Dave

[shopratles]

Originally Posted by MrDavidOgle

ShopRatles, is the "intake rail gasket" - the rubber seal that goes on the back end (closes to firewall) of the intake manifold - between the block and the intake? Is this end of the intake manifod pressurised with oil? Would this much oil be able to leak at the rear of the intake manifold - obviously when under pressure when the engine is running? When I installed the rubber intake manifold gaskets, I put a light bead of red silicone on both sides of the rubber gasket and a heavy bead on both ends of the gasket filling any room for leak between the head gasket and this rubber intake gasket (I did the same thing on the front and back of the intake manifold gasket)... But, as you suggest, I cant be 100% positive that it didn't slip out of position during installation. The front doesnt leak oil!Dave

Yes, that is the rubber seal I am referring to. The oil under the intake manifold is not under pressure either, but you wouldn't believe how much is under there flying around. Your oil pan can be leaking also but it would be localized in that area (ain't gravity wonderful?). If it is the cam plug on the back of the engine, you will need to pull it out and replace it. There is no oil seal and you could have knocked it out of position if you hit it too hard during installation of the cam. Check the intake rubber seal first as it is easier to see/feel. FYI...when I had a rear main go out I was loosing about a quart of oil every 50 miles, but yours might not be so bad. Good luck.

[chevyguy]

Before replacing antything, Verify where the leak is coming from. Can you get a small mirror in behind the block and see if it is froom the top portion(intake) or from down around the crank, or cam area.

[hotrod69]

I Agree If The Leak Was Coming From The Top Of The Engine It Would Be Leaking Off The Bell Housing And Surrounding Areas It Might Be Wize To Do What Chevyguy Suggests And Get A Small Inspection Mirror In There And See Were The Most Evidence Of Oil Is Comming From If U Have Had The Pan Off And Changed The Seals Back There It Should Not Be To Hard To Spot The Fresh Markings Of Oil The Other Thing U Could Do If U Can Not See Were It Is Coming From But U Know It Is Coming From Between The Engine And Tranny Separate The Tranny From The Engine Far Enough To Run The Engine With A Better View (but Support The Engine Well Enough As Not To Cause A Problem) Besides That Way When U Do Find The Leak Half The Work Is Already Done.

[72'CaminoKid]

hotrod, that sounds like a good idea, but my only question is how do u start it with the tranny bein gone? my question spurs from the fact of most starters bein bolted to the tranny...... i'm not sayin you're wrong in ur idea ( for all i know you've done it b4 and know it works) i'm just ignorant as to how to start it that way.....