Fixing Leaky Intake Manifold (Part 2)

[bostonbronconut]

I brought my '77 Bronco to a local mechanic to help resolve an issue of leaking oil/fluid but they wouldn't work on it because of the "risk of starting a fire", which sounds like they just didn't want to actually work on it. Some of you may have already seen the post I started today regarding my '77 Bronco not starting. I started that post because oil is pooling in the well behind the intake manifold. As mentioned earlier, I tightened all accessible manifold bolts with a torque wrench, dried out the puddle, and then took the Bronco out for a quick ride. Unfortunately, the pooling started again after a short trip.

I replaced the intake manifold gaskets a few years ago in hopes of resolving a potential coolant leak and oil leak. Unfortunately, this might be the cause of the pooling I am getting at the moment and why the mechanic wouldn't touch the Bronco (). I used Permatex Ultra Balck Oil Resistance RTV instead of replacement Fel-Pro front and back gaskets during the gasket replacement but I'm concerned that I didn't use enough given the leak.

I've attached a photo of the back of the manifold and it does look like there is enough RTV (Sorry, it isn't the best image; not an easy task). Is the RTV the most likely culprit or do you think it is something else? I'd like to avoid pulling the intake manifold off (again) so are there other things to check? If you think that the RTV is the culprit, are there any potential repairs that can be done prior to removing the intake manifold? Thanks as always!

 

[73azbronco]

Risk of a fire, what is it powered by Tesla batteries?

Seriously, not using the front and rear seals which is normal, it looks like there was not enough sealant used. The technique I think works best is apply liberal amount of sealant, let it set up for ten minutes or so, install intake, lightly tq bolts, and after another hour or so tq to spec. I think more sealant should be pushed out.

Only other possible issue is your intake is not fitting correctly. Block milled? That “raises an intake because heads are closer together.

 

[Wild horse 75]

First don’t use RTV. Spend the money go buy The Right Stuff. Second when you’re running a bead what I do is I run a fat bead down on the block that goes the full width of the block. Then I go back and run a small bead down the centre of the fat bead. That way there will be plenty of height and width but not so much that it seriously overflows. The fat bead needs to just be the width don’t worry about making it thick height wise, that’s what the small bead is for. And since you won’t be able to make the thick bead in on continuous squeeze any small imperfections will be fixed up by the small continuous bead on top. I’ve been doing it that way for 20 years with almost 100% success (some intakes just leak cause the design sucks) but on SBF it’s never failed me.

 

[bostonbronconut]

Risk of a fire, what is it powered by Tesla batteries?

Seriously, not using the front and rear seals which is normal, it looks like there was not enough sealant used. The technique I think works best is apply liberal amount of sealant, let it set up for ten minutes or so, install intake, lightly tq bolts, and after another hour or so tq to spec. I think more sealant should be pushed out.

Only other possible issue is your intake is not fitting correctly. Block milled? That “raises an intake because heads are closer together.

It is my guess that I didn't use enough sealant at the rear of the manifold. I used posts to make sure that the manifold was placed correctly.

Re: Block Milled - I don't think it was. The previous owner mentioned boring the engine to 351 but nothing about milling the block. I've attached images of my original gasket replacement for reference.

Do I have any options that do not require removing the intake manifold? As mentioned before, I already tried retorquing accessible bolts down to 20 ft-lb. If the back sealant is the culprit, can I change the oil, clean the area, and add a new layer of RTV/Right Stuff to plug it or will it not hold?

 

[DirtDonk]

Probably won’t hold.
However, nothing says you can’t try it. It is, after all, the least intrusive thing you could do at this point.
Don’t have to change the oil though, and I wouldn’t. Clean the area very good maybe slice off some of that extra sealant sticking out (or not), apply a liberal amount to the whole area along the back edge of the manifold, and let it cure for a minimum of 24 hours before you start driving.
If it works, even temporarily, you’ve put off removing the manifold for awhile.

But speaking of the manifold…
Generally speaking, you never just torque the bolts that are visible. To do an intake manifold correctly, you have to do them all to the same level. And in a specific torque sequence.
Once its torqued down, like it has been now for awhile, you probably don’t have to follow the torque sequence as diligently as when you were installing it for the first time.
But you still don’t want to tighten just some if it can be avoided.
Sometimes you have to, but usually better to spend the extra time and get the other stuff out of the way.
How many were you able to get to?
And were they loose?

And to clarify some potential misinformation you were given by the PO, you can’t bore out an 302 engine to 351. The main difference, and with any engine that much difference is usually handled by stroking the engine.
So either they were lying to you, or they were mistaken, or you’re remembering it incorrectly.

Perhaps they did bore it out, but typical bore jobs net you with something in the neighborhood of 306ci instead.
The engine blocks would not tolerate a boring that gave you almost 50 ci.
And most stroker engines don’t quite reach 351ci either.
Although they do get pretty close at 346.

So, unless it’s actually a 351 block, you still have a 302 that might have been bored over a little bit.

 

[DirtDonk]

And just for giggles, did you also re-tighten your valve cover bolts?
Those are an extremely common leak area on our engines. But typically they leak downward, and not over towards the center of the block.
However, it never hurts to check.

 

[bostonbronconut]

Probably won’t hold.
However, nothing says you can’t try it. It is, after all, the least intrusive thing you could do at this point.
Don’t have to change the oil though, and I wouldn’t. Clean the area very good maybe slice off some of that extra sealant sticking out (or not), apply a liberal amount to the whole area along the back edge of the manifold, and let it cure for a minimum of 24 hours before you start driving.
If it works, even temporarily, you’ve put off removing the manifold for awhile.

But speaking of the manifold…
Generally speaking, you never just torque the bolts that are visible. To do an intake manifold correctly, you have to do them all to the same level. And in a specific torque sequence.
Once its torqued down, like it has been now for awhile, you probably don’t have to follow the torque sequence as diligently as when you were installing it for the first time.
But you still don’t want to tighten just some if it can be avoided.
Sometimes you have to, but usually better to spend the extra time and get the other stuff out of the way.
How many were you able to get to?
And were they loose?

And to clarify some potential misinformation you were given by the PO, you can’t bore out an 302 engine to 351. The main difference, and with any engine that much difference is usually handled by stroking the engine.
So either they were lying to you, or they were mistaken, or you’re remembering it incorrectly.

Perhaps they did bore it out, but typical bore jobs net you with something in the neighborhood of 306ci instead.
The engine blocks would not tolerate a boring that gave you almost 50 ci.
And most stroker engines don’t quite reach 351ci either.
Although they do get pretty close at 346.

So, unless it’s actually a 351 block, you still have a 302 that might have been bored over a little bit.

Re: Retorquing - When I first reinstalled the manifold the first time I followed the correct torquing sequence. I only retorqued the accessible bolts yesterday to see if that resolved the leaking issue or at least slowed it down. I don't mind putting in the work to do something right but I was hoping that by tightening accessible bolts to 20 ft-lb I can save myself a big job. I was able to get to about eight of the 12 bolts; most of them required a few turns before the wrench started clicking.

Re: Bored Engine - I was actually able to find one of the notes from when initially chatting with the PO: "Engine was rebuilt with a “mild” truck/SUV cam and has the firing order of a 351W (the engine is a 302 bored .030”)"

 

[bostonbronconut]

And just for giggles, did you also re-tighten your valve cover bolts?
Those are an extremely common leak area on our engines. But typically they leak downward, and not over towards the center of the block.
However, it never hurts to check.

I have not tried re-tightening the valve covers yet due to the reason you mentioned (i.e. leaking downward and not toward the center of the block). However, I have noticed some dried fluid near the PCV valve, I think it might be some coolant from the Bronco heater valve located right above it.

 

[DirtDonk]

OK, I see where the 351 reference came from. Sounds like a good update.

What’s in your other valve cover? Looks you have the PCV valve located where the 66 to 70 models had it, with an air cleaner from a 71 through 77. Is that sound correct?
Since this is a 77 it probably has the correct air filter. But the 77 would’ve had the valve in the driver side valve cover in the low profile oil filler cap.
And the passenger side where you were showing would’ve had a 45° elbow hose fitting that had a short length of hose going to that other plastic hose fitting or you can just see in the picture hanging out of the bottom of the air cleaner.

 

[bostonbronconut]

OK, I see where the 351 reference came from. Sounds like a good update.

What’s in your other valve cover? Looks you have the PCV valve located where the 66 to 70 models had it, with an air cleaner from a 71 through 77. Is that sound correct?
Since this is a 77 it probably has the correct air filter. But the 77 would’ve had the valve in the driver side valve cover in the low profile oil filler cap.
And the passenger side where you were showing would’ve had a 45° elbow hose fitting that had a short length of hose going to that other plastic hose fitting or you can just see in the picture hanging out of the bottom of the air cleaner.

The PCV valve is located on the passenger side and the air cleaner is a factory air cleaner assembly. The PCV has a 90° farther down the cover and then feeds into the carb. The driverside valve cover has the oil filler tube with cap.

I've attached a photo of the engine without the cleaner.

 

[DirtDonk]

The PCV valve is located on the passenger side and the air cleaner is a factory air cleaner assembly. The PCV has a 90° farther down the cover and then feeds into the carb.

Thanks for the pic. The PCV is still working, but it "should" be in the driver's side.
Not because the engine cares which side of it gets the bad gasses removed, but because the factory air cleaner is expecting a filtered air return there on the passenger side.
Are you capping that angled fitting on the air cleaner? If not, you are constantly sucking un-filtered air into the engine. That fitting is INSIDE the main filter, so there is nothing between it and the engine internals.
Short term, not really an issue unless you drive in very dusty conditions. But long term? If it's been this way a long time then some damage has likely already been done.
Maybe not the end of the world, but definitely something to fix right away.

The driverside valve cover has the oil filler tube with cap.

Looks like a standard cap from here. Is there an opening and filter media inside it to keep outside air clean before it gets sucked into the engine? If not, it's the wrong cap.
Sometimes this type of cap is messy, because it collects oil vapors and splash from under the cover and lets it drip out on the outside of the cover. Yours looks pretty clean, so I wonder if it's actually a vented/filtered cap, or just a cap.

Not sure why things were reversed and set up this way, but it was probably due to the new valve covers. If the factory cap did not fit into the new covers, a new plan was needed.
You just need to make sure that clean air is being constantly sucked into the engine. From either side...

Here's what your original driver's side filler cap would look like: Oil Filler Cap w/ Elbow
The elbow fitting would be in the passenger side, and the PCV valve would fit into the same grommet in the cap.
From the driver's side it's even easier to connect to the front of the carburetor, and having the elbow on the passenger side lets you connect a hose between this elbow and the one on your air cleaner housing.

Paul

 

[bostonbronconut]

Re: Oil Cap - It is the Scott Drake FoMoCo logo push-on cap. It states on the the product description, "This style oil cap will also function as a breather cap and can be used on all open emission Broncos." It looks like the filter is a bit dirty though. I think a good cleaning will be beneficial (see photo).

Re: Factory Air Cleaner - My factory air cleaner has a filter so it brings filtered air in albeit from the engine compartment. I have the fresh air tube and hot air pickup tube but I haven't gone around to installing them yet.

From what it sounds like, you'd recommend swapping the valve covers, right? I looked at a bunch of Broncos on BaT and I did notice there were a bunch of rigs with the PCV on the driverside. I might as well put in new gaskets while I'm at it.

 

[DirtDonk]

No need to swap covers. If the two side's fittings don't interchange, just leave them the way they are. The cap you have is filtered (albeit not super fine), so that's a good thing. It lets clean-ish air in after it's sucked out by the PCV valve.

If the valve covers have the same size and shape holes, there's no need to swap.
What does your driver's side cover look like without the breather installed?

The fitting on the air cleaner housing I was speaking of is not pictured in that last diagram.
The one I'm talking about is just visible in your picture in post #8 under the air cleaner and partially painted blue.

Paul

 

[bostonbronconut]

All of this is now starting to make sense. In a perfect world, the oil cap would have a 90° elbow breather that would connect to the housing on the air cleaner. Given the location of the oil filler tube, I'm guessing it was easier for the PO to use a breather cap with a filter instead of routing a hose around the back of the engine.

The driver side cover has an oil filler tube like the one in the attached photo.

 

[DirtDonk]

Right. I forgot those valve covers had the chimney.
I should’ve realized as soon as I saw your breather.

 

[DirtDonk]

But you still need to cap off that elbow that’s attached to the air cleaner housing.
Otherwise you’re just sucking outside air in past the filter.

Do you have the other plastic fitting, the one facing the passenger side? In the picture of the 77 air cleaner assembly it’s missing, but you can see the round hole that it fits into.
That would normally be for the charcoal canister vent tube.

 

[bostonbronconut]

Good call on capping that elbow on the air cleaner.

Re: Plastic Fitting/Charcoal Canister - I didn't even know I had a charcoal canister. I found a vent drain tube on broncograveyard.com; is that what you are referencing?

In the meantime, I am going to dig around the engine bay to try to find said canister.

 

[DirtDonk]

From 70 to 75, the canister was a round metal can bolted to the passenger side frame rail with a strap and rock shield. Located at the back of the front wheel well opening.
For 76 and 77 that was replaced with a rectangular plastic canister bolted to the firewall on the passenger side, just behind the wheel well.

Many of them have been eliminated by owners over the years, as just some more of that “stupid smog crap” so don’t be surprised if yours doesn’t have one.
But it did from the factory…

 

[DirtDonk]

I found a vent drain tube on broncograveyard.com; is that what you are referencing?

Nope. That is just what it says. It is a vent drain.
That is a drivers side fresh air vent drain so that water that gets in through the hood grille has a place to drain out onto the ground.
Instead of building up inside and flooding the passenger compartment.

 

[Oldtimer]

I found a vent drain tube on broncograveyard.com; is that what you are referencing?

The fitting you need is D0AZ-9D692-B (or C, different color)
Internet search turns up plenty of NOS.