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Best way to seal intake manifold

12K views 13 replies 11 participants last post by  67_LS1 
#1 ·
I’m going to replace the intake manifold gaskets on a buddies boat with a small block 350. What’s the best way you’ve used to seal the manifold? It’s currently leaking oil down the back of the block.
 
#3 ·
If that is leaking on the end seal you may not need to remove the intake.
I have used Ultra black and Ultra grey with NO oil leaking issues for many years.
Buddy stuck on a tunnel-ram and thought his oil sender was leaking and it was not the sender after 6 attempts at trying to make it stop leaking.

The silicone Ultra black got messed up during intake install.
I fixed the leak by cleaning the area with carb cleaner and compressed air then taking paper towels and wiping any residue up.
If you still have oily residue you need to give it another cleaning and blow out with air.

I then took a shop vacuum and hooked to the pcv port on the valve cover.. or oil fill cap on valve cover.

The vacuum will pull about 3" of vacuum if things are sealed up.

With vacuum on take some Ultra black and squeeze it out on your finger and tamp the sealant into the area where the intake is leaking.
The vacuum will slightly pull in some of the sealant.
Shut off the vacuum and tamp some more sealant into the leaking area and let it set up 24 hours.

Or pull intake off clean everything very well and install new Felpro intake gaskets and only use Ultra Black on end seals and around water ports.
Thin Thin Thin amount around water ports.
Only enough to fill in the pitting and a skin.

On end seals make sure the silicone is still wet when assembling it.
If you let it skin over on the end seal area and then stick the intake manifold on the skinned over sealant will not grab and stick to the intake and now you have a path for oil to leak.
Needs to be fresh and sticky to make a great seal.

Where the intake meets up with the block at the end seal area I like to tamp silicone into that tiny area with my finger as sometimes if you just lay a bead out of the tube it will not fill that tiny spot.
 
#4 ·
You need t make sure that it is actually the intake leaking. It could be the oil pressure sender or something else. I would clean it off real good with Brake Clean and put some die in the oil and then run it for a while and take a look.

If it is the intake I go along with what most others do. I use the Permatex Right Stuff on the front and back rails. I might put a little bit around the water passages if it is not a Vortec engine. On the Vortec engines I use the updated metal gasket and pretty much put it on dry. I prefer to let the Right Stuff sit for a few days to cure before running the engine if possible.
 
#7 ·
One of the great things about the RIGHT STUFF is that is designed to be put into service immediately. That’s why it cost more. And I must say I’ve done that many times, and I’ve never had a leak!
 
#9 ·
Use good gaskets like Felpro 1205 or equivalent, toss the rubber or cork strips for the ends (China wall). Use permatex ultra grey rtv or the right stuff on the China wall, make sure to overlap the rtv to the lower gasket tangs. Use a very thin coating around the water jackets.
 
#10 ·
Three-Bond 1194, same stuff that is set on good intake gaskets around the water ports. This stuff works well with, or without gaskets in place, sealsd up engine cased on motorcycles that have no gasket but the Three-Bond, and on intake ports, all other stuff with gaskets. DOESN'T WORK with exhaust heat, though, so, don't add it to an exhaust area.
 
#11 ·
As with everyone above, start with a clean, oil/grease free surface. Red Brakleen will remove all the oily residue from the surface and dries quickly so you can get the work done.

If you find it's the rear of the intake and you want to seal it without removing it, bring along an old toothbrush, use it with the brakleen to get the area clean before applying RTV.
 
#13 ·
One thing I neglected to mention for the Three-Bond on intake GASKETS, it is not suitable for the end seals, they are better made from a tube of silicone seal, as we are all aware is done regularly. The Three-Bond is for the actual gaskets. I apologize if this caused any confusion, wasn't meant to.
 
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