Thread sealant on header bolts?

David King · Nov 25, 2024

The passenger side valve cover should have two holes in it. The one nearest the firewall is for the crankcase breather tube going into the the air filter housing, the other toward the front of the truck is a larger hole that allows oil to be poured into the engine. The driver side valve cover has one hole for the PCV valve. I recognized this descrepancy in the LMC catalogue and informed LMC and they said they would confer with the "experts" and correct the issue regarding '85 C-10's chrome valve covers.

Truck82 · Nov 25, 2024

Ricko1966 said:
On cheap chromes I've never had luck unless I take the right angle die grinder th the sealing surface on the valve cover to rough it up good,then I glue my valve cover gasket to the valve cover it's self with 3m super weather strip adhesive and use grease on the other side of the gasket where it meets the head. Those valve covers should have spreaders on the retainer bolts,do you have them? You are missing 1 hole on the valve covers so how do you have them installed. Hole on PS side valve cover should go to pcv breather,hole in other valve cover should go to pcv valve. If you plugged either of those holes,you are going to have leaks,if that breather is plugged you are going to have leaks. If you plugged them both you are going to have big leaks. You will have to fill through the vent or the pcv hole. Unless you have an early manifold on your truck.

I’ve got the little spreaders under the bolts. I have a PVC valve in the driver side and a breather cap in the other. I don’t know how well the pictures are but you should be able to see the oil soaked on the back of the exhaust manifold and that far back bolt.

Truck82 · Nov 25, 2024

David King said:
The passenger side valve cover should have two holes in it. The one nearest the firewall is for the crankcase breather tube going into the the air filter housing, the other toward the front of the truck is a larger hole that allows oil to be poured into the engine. The driver side valve cover has one hole for the PCV valve. I recognized this descrepancy in the LMC catalogue and informed LMC and they said they would confer with the "experts" and correct the issue regarding '85 C-10's chrome valve covers.

I have an open air cleaner. Does that still affect the crankcase breather tube?
Check out my pictures in my last post

Turbo4whl · Nov 25, 2024

@Truck82 Assuming the bolt is the source of the leak, then the head probably has a flaw in the casting or a crack. When you remove that bolt, are the threads oily?

To seal the leak install the bolt with Permatex. Use either number 2 or 3. Silicone will not last. Number 3 Permatex also know as aviation Permatex is probably easiest to apply as it has a brush in the lid of the container. No. 3 is also my go to for sealing leaking valve cover gaskets. Coat both sides of the gasket.

Ricko1966 · Nov 25, 2024

Wipe the area between the breather and the oil spot with a rag. I'll bet oil is venting from the breather and running down.

Truck82 · Nov 25, 2024

Turbo4whl said:
@Truck82 Assuming the bolt is the source of the leak, then the head probably has a flaw in the casting or a crack. When you remove that bolt, are the threads oily?

To seal the leak install the bolt with Permatex. Use either number 2 or 3. Silicone will not last. Number 3 Permatex also know as aviation Permatex is probably easiest to apply as it has a brush in the lid of the container. No. 3 is also my go to for sealing leaking valve cover gaskets. Coat both sides of the gasket.

I pulled the bolts out when I rebuilt the heads in the spring and a few of the bolts in the back leaked quite a bit of oil. Knowing very little then, I didn’t think anything about it and just assumed that was natural. I installed them with a liberal amount of Permatex thread sealer and called it good. Now they seem to be leaking again. When I take the old manifolds off to put my long tubes on I’ll check for sure if it’s coming from the bolt. At least for now only one is leaking. We’ll see how the others hold up. I see no oil coming from the valve covers.

Ricko1966 · Nov 25, 2024

I can tell you for 99.99999 percent positive that you aren't leaking oil from the exhaust bolts them selves the only oil in a SBC head is what pools up top from the pushrods. The exhaust bolts are well below that. The bolt holes are blind holes,and even if someone managed to break through the back off one,the area behind the exhaust bolts would hit a port a guide or a water jacket. If you have one leaking oil it would be an absolute once in a lifetime freak happening.

PrairieDrifter · Nov 25, 2024

Looks like I can see the path the oils taking in those pics. Looks like it's running straight down from the valve cover. Don't know how new your paint is or if that's a stain or what? But that's what i see.

v30 · Nov 25, 2024

I use nord locks on header and exhaust manifold bolts. Works well hard to get back off if per say your header had to be removed to replace a starter.

Truck82 · Nov 25, 2024

PrairieDrifter said:
Looks like I can see the path the oils taking in those pics. Looks like it's running straight down from the valve cover. Don't know how new your paint is or if that's a stain or what? But that's what i see.

I believe that’s condensation? I didn’t see that before and as you can see on the valve covers, it’s very wet here. Now I’m thinking “is that oil!?!?”

Truck82 · Nov 25, 2024

Ricko1966 said:
I can tell you for 99.99999 percent positive that you aren't leaking oil from the exhaust bolts them selves the only oil in a SBC head is what pools onto from the pushrods. The exhaust bolts are well below that. The bolt holes are blind holes,and even if someone managed to break through the back off one,the area behind the exhaust bolts would hit a port a guide or a water jacket. If you have one leaking oil it would be an absolute once in a lifetime freak happening.

I didn’t think they would run into the oil passage. But I’ve for sure had oil run out of multiple bolts before. Don’t know what this would be

PrairieDrifter · Nov 25, 2024

Truck82 said:
I believe that’s condensation? I didn’t see that before and as you can see on the valve covers, it’s very wet here. Now I’m thinking “is that oil!?!?”

Looks like oil to me. Condensation would burn off right away. That's like a dust trail from oil, on the head surface that is.

In the last picture that spot on the manifold is right in front of a spot that looks like oil leaking(behind spark plug holder).

Also an intake gasket can also leak and flow around the valve covers sometimes. But the back of the heads will get real greasy first.

Thread sealant on header bolts?

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