Front "China wall" sealing issue on SBM

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MopaR&D

MopaR&D

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I have a 5.9L Magnum short block in my '70 Duster with Edelbrock open-chamber heads and RPM non-Air Gap intake. I have a recurring issue where oil is leaking out from the area on the passenger-side bank where the head, block and intake mate together. I assembled the engine using the 'big bead of RTV' method to seal that area like is commonly done with aftermarket intakes and heads. It started leaking not long after getting it running so I pulled the intake and carefully cleaned and liberally re-applied black RTV to the area; it didn't last long and started leaking again the same as before. The leak isn't that bad unless the engine is running at higher RPM (above 4000 or so) so I've just been turning a blind eye since then but I want to start taking it to some local track days and I know running on a road course it's going to be spending a lot of time in the higher revs; I don't want to get in trouble for leaking oil on the track and/or running low on oil. Plus it's just irritating as hell and makes a mess. Anyone have some tips on how to reseal it and make it actually STAY sealed this time around? I've moved on to using black Right Stuff sealer upon recommendations of others which I will use for this job. I also recently found a YouTube video by Dead Dodge Garage where he had the exact same issue on a 340 running these same heads and a Weiand (iirc) intake manifold, he hasn't reassemble the engine yet though so I'm not sure if he has a solution in mind.

He first starts talking about the sealing problem around 3:30-4:00-ish mark...

 
I looked full screen at 16 seconds. It doesn't look like the silicone was even compressed. The Professor may be right. I bought a used stroker a few years back. the pins were still in and there was a couple tubes of silicone to seal the ends. What a mess.
 
You mean the roll pins that go into the block? Yes those are long gone. I'll check again when I get around to taking it apart but IIRC I had to remove those anyway as they were interfering with the intake manifold seating down onto the heads; intake manifold mating faces were milled because it sat too high for the bolts to thread in.
 
I'm betting it has something to do with the intake machining. Not quite the right angle, maybe? How are the ports sealing? Even pressure on the gaskets?
(I would be tempted to put one bead of perm gray, let it set quite well, then add another)
 
MopaR&D said:
You mean the roll pins that go into the block? Yes those are long gone. I'll check again when I get around to taking it apart but IIRC I had to remove those anyway as they were interfering with the intake manifold seating down onto the heads; intake manifold mating faces were milled because it sat too high for the bolts to thread in.
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I have sealed many intake China walls with silicone. Pins and a stock intake (with the holes to accept the pins) and aluminum intakes with no holes (and the pins removed). Dry fit the intake with the gaskets you will be using and check for proper bolt hole fit. You can see the gap on the china walls and whether you need a cork end seal or silicone. A narrow to medium gap can be sealed with silicone. I would say if you have 3/8- 1/2" gap you might want to think about the cork gaskets. I don't like to use them but I don't like sealing inches with a bead of silicone. Clean and dry all surfaces with brake clean and squeeze out a proper sized bead. Less for a narrow gap and more for a bigger gap. (of course) Install the intake and torque it down. Let it sit overnight (at least) before adding coolant or running the engine. This has worked for me many times.
 
Mock it up. Install the gaskets and set the intake on and see how much of a void you have at the China walls and see if the corks will slide if. If so use them and apply a layer of Silicone to each side and blobs on the ends. If you have a small gap and they don't fit at all, re-silicone the wall to intake area and work hard not to get air voids in the silicone. Use a brand new fresh tube too.
 
Right stuff will seal it. Run the bead up and over the tabs of the intake gasket. I also put a dab under the intake tab to seal the corner. In the video it looks like he stopped way short with his bead and it leaked right at that spot. I usually let the right stuff tack up a few minutes but that’s all. Plop the intake straight down, lightly install bolts, let sit a half hour or so, then tighten the bolts.
 
Also note the odd way the intake and block come together in that corner.
The RTV bead needs to have a special curve there to contact both surfaces.
 
It leaks worse at higher rpms? Do you run a pcv valve? I've used copper rtv on the china wall on my last three small blocks and haven't had a leak. Clean, clean and clean, then allow plenty of time for the rtv to cure.
 
Place the intake on the engine with everything CLEAN and no gaskets and see how much of a gap you have at the chink walls.
 
Thanks for the tips guys, I should have at least one of the cork front gaskets lying around and if the intake sits low enough to compress it I'll use that, with RTV of course. If not I'll be extra careful with the RTV bead this time to make sure it covers all the leak points well, build it up in the corners and run it towards the back farther.

@justinp61 I am running PCV but with this heads/block combo I had to make an external rocker oiling setup and I think it's over-oiling the top end and making lots of windage at higher RPM which is splashing on the underside of the intake manifold. The oil flows through custom hollow rocker shaft bolts at the back and I think the hole in them to restrict flow isn't small enough. Next project is to bring some new bolts into work and drill them on our nice lathe with smaller holes.
 
MopaR&D said:
Thanks for the tips guys, I should have at least one of the cork front gaskets lying around and if the intake sits low enough to compress it I'll use that, with RTV of course. If not I'll be extra careful with the RTV bead this time to make sure it covers all the leak points well, build it up in the corners and run it towards the back farther.

@justinp61 I am running PCV but with this heads/block combo I had to make an external rocker oiling setup and I think it's over-oiling the top end and making lots of windage at higher RPM which is splashing on the underside of the intake manifold. The oil flows through custom hollow rocker shaft bolts at the back and I think the hole in them to restrict flow isn't small enough. Next project is to bring some new bolts into work and drill them on our nice lathe with smaller holes.
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Using cork with RTV is not a good idea. The RTV will act as a lubricant and the cork will slide out from under the intake as you torque it down. If you use anything use something like 3M yellow weatherstrip adhesive and glue the cork to the block with nothing on top of the cork. You'll also want to put a small dab of RTV in each corner where the heads meet the ends of the china walls.
 
I wouldn’t use cork at all. They always leak. Just use right stuff and it will seal.
 
Cork with sealant if the gap is too big. Use the cork on both ends, and don't forget the cork usually comes with sticky stuff on the bottom. You just peel off the paper and stick it in place. You need sealant around the water ports and corners.
 
Never had cork leak after an intake install. Best cork versions were the Felpros with the.....never mind^^^^^^^^. In lieu of that some spray adhesive works if the gaskets don’t have the adhesive (block side only) China walls need to be degreased thoroughly before affixing. Then RTV black in the corners. There’s a difference between correct (sparingly) use of the RTV and over application in some cases.

Don’t go cutting the end of the tube off and using your elbow to spread it. (Just an expression we used in my construction days using caulk doing siding, kitchens and baths) :eek:
 
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I'm old school. We center punch random divots along the block china wall and the intake to hold the gaskets in place.
Indian Head (I know not PC) gasket sealer along both block and intake. Only rtv in the corners,let it set awhile before installing the intake.
Don't do any of that if you plan on removing the intake in the near future.
 
I found this on my recently built (previous owner) 390. I found the tabs for the head gaskets were still sticking up and the intake would rock on those. I removed them and it sits really nicely now. Per RustyRatRod I used two beads of rtv on the front and back and it looks to have been sealed up nicely.

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Sand the aluminum Intake china wall seal area with 180 grit sand paper to give the RTV a place to bite.

Of course Brake Parts Cleaner all sealing surfaces, no oil films.

Then Aviation Sealer on the intake manifold mounting Bolts and threaded holes as they go into the oil side of the block.

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I would sand the China wall area on the block with 180 to get down to good clean raw iron to help it seal for good measure too.

Good Luck

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I also cut out the Head Gasket Tabs clean into the Head/China Wall corner with a razor knife once the heads are installed.

This allows the RTV sealer to go all the way into that leaky corner and seal it.

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RustyRatRod said:
Using cork with RTV is not a good idea. The RTV will act as a lubricant and the cork will slide out from under the intake as you torque it down. If you use anything use something like 3M yellow weatherstrip adhesive and glue the cork to the block with nothing on top of the cork. You'll also want to put a small dab of RTV in each corner where the heads meet the ends of the china walls.
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I used that on a cork oil pan gasket on the first 383 I built. When I had to tear it back down later I had a heck of a time getting the remains of the gasket and cement off the block. I haven't used in the 45 years since.
 
justinp61 said:
I used that on a cork oil pan gasket on the first 383 I built. When I had to tear it back down later I had a heck of a time getting the remains of the gasket and cement off the block. I haven't used in the 45 years since.
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Yeah. It's pretty tough. But if you want something to STICK, it works.
 
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