Intake Leak

[sireland67]

I think your going to trace it back to bad machine work ,possible wrong angel cut some were another note are your intake bolts too long bottoming out giving the appearance of being tight with all that cutting on everything or the shoulder bottoming out on the bolts, just another thought. also check to see how tight the bolts are going through the intake manifold you may need to open them up some to let the intake move smoothly when torqued down and not bind .

X2 I always thought for every .010 you took off the block you take .012 off the intake.
I would say your intake or heads are milled crooked.

FYI I used a metal gasket on my un-milled 318 in my truck with a old un-cut LD4b intake.
Even using copper spray gasket on the metal gaskets, it started leaking in a couple of weeks.
Put a premium fel-pro gasket on it, I think it was around .030 thick, copper sprayed it. The bolts were a complete ***** to get in, but two years later it does not leak.

Apparently my intake was not manufactured straight, and if a machinist just run a dial indicator across the edge of yours, it most likely is not square with the heads.

You can pick up a cheap angel finder at any hardware store, and check head, vs intake angle, use copper spray on the intake it really works.

 

[bobscuda67]

Well I installed poster board on the heads intake surface and used dye to see how the intake seals on the head. The intake seams to seal around the ports ok. I guess I'll buy an angle finder next.

 

[7e5hangten360]

could it be the valve covers or valve cover gaskets preventing the intake to sit down in its place? judging by the pictures, its awfully close. it happened to me and i had to grind the top of the intake just under the valve covers for clearance.
also, check for cracks on the intake. good luck.

 

[bobscuda67]

could it be the valve covers or valve cover gaskets preventing the intake to sit down in its place? judging by the pictures, its awfully close. it happened to me and i had to grind the top of the intake just under the valve covers for clearance.
also, check for cracks on the intake. good luck.

Thanks for the input, but there is just enough clearance under the covers. I don't think there's any cracks as I've had this intake for 5 or 6 years and it's been fine. I drove my car 400 miles last year and never had a leak. The problem started when I had the block decked .015 last winter and this summer it started leaking. So it's looks like an angle issue to me, it might only be a few degrees off as it did last 100 miles before it started leaking the last time I replaced the gasket in September.

 

[Inertia]

This may work for you, maybe not.. Back in the day,, we used to glue copper armature wire around the embossed steel head gskts to make an "O" ring seal around the cylinders..

Perhaps you could glue similar wire around each port, overlapping the ends, and it would just sink into the gskt material where needed,, if you get my drift..

hope it helps..

 

[bobscuda67]

I bought an digital angle finder today and nothing really jumps out as a angle problem.

Left side block to head is 47.80 degrees.
Left side intake is 47.60 degrees.
Right side block to head is 47.40 degrees.
Right side intake is 47.50 degrees.
Anyone see where the machining would cause a sealing problem?

 

[Bad Sport]

I'm just spitballin here, but you milled the heads. Is it possible it's just enough to not let the 4 corners set down properly, holding it up enough to not allow it to seal?

If you set it on there dry, how much, if any, space is between the bottom of the intake and the pad on the block, front and rear?

Locator pins?

 

[Inertia]

While the intakes sittin on there without a gskt,, do all the manifold bolts go in and start..?

also spit ballin

 

[bobscuda67]

When the intake is sitting on the block without the gaskets installed there is no space from the bottom of the intake to the block's china wall. And there is .012 gap between the head and the intake. But when the gaskets are installed there is 1/8th. inch of space under the intake.
The locator pins don't bottom out in the intake either.
The bolts thread in by hand when there isn't a gasket installed.
This has got me stumped.

 

[Bad Sport]

Well, you may have unwittingly found your problem.

I just walked aaalllll the way out to the shop (about 50 feet lmao) and here is what I did.

I opened my brand new Felpro gasket set for the engine and I put my untouched LD340 on my 360 SB with stock J heads.

I got 3/16ths of an inch without gaskets from bottom of intake to wall.

View attachment without gasket.jpg

And with a gasket I got 5/16ths of an inch from bottom of intake to wall. Kinda hard to see, the dang flash went off.

View attachment with gasket.jpg




I bet dollars to donuts it's bottoming out before it can compress and seal the gasket.

 

[Bad Sport]

And just an FYI, when I had the gasket on, under the intake, the bolt holes were just a tad higher than the ones in the heads. Which, they should be, because when you snug them down they pull the intake down which provides the clamping force needed to seal the gaskets.


Perhaps you need to find a thicker gasket to raise it some, if they make such an animal.

 

[bobscuda67]

When I removed the intake when it starts burning oil there is about 1/8 inch thick RTV on top of the block that seals to the bottom of the intake. If it bottomed out the RTV would squeeze out.
Now a thicker gasket might be needed, that I could try. Maybe one that will compress more than the .060 Edelbrock gasket I used first.
I am using Magnum heads and the bolts pull the intake down tight.
Thanks for taking the time to try and help me Bad Sport, I appreciate it.

 

[Bad Sport]

I didn't read each post thoroughly, but I didn't see any mention of sealant.

Are you using a good NON hardening sealant on the intake bolts when you put it together?

If not, try it. Sometimes oil can wick up the bolt threads and get sucked in, which would give you the symptoms your are seeing.

Have you noticed any trace of oil on the intake??

And, I assume you have put a flat edge on the intake mating surface, and the head mating surface? I would guess they did that at the machine shop when they milled the heads, but you never know.


I use this:

 

[7e5hangten360]

i think we are on the wrong track here with the intake not sealing right after all ive seen and read and so many intake gaskets. im thinking oil could get from the pcv valve in the intake. block the pcv and go for a ride. maybe all you need is a baffle in the valve covers. another possibility would be bad valve seals/guides. at least try it with the pcv blocked.

 

[bobscuda67]

Yep, I have non hardening sealant on the bolts and the head's intake surface was milled a few years back and is flat. The intake surface was milled .015 in August and is flat.
I cleaned the PCV and it's working properly and I have a baffle in the valve cover.
I find the oil in the heads intake ports when I dissemble it when it starts burning oil. You can see the oil gets sucked through the between the gasket and head as any type of sealant that I used was gone and there is a trail of oil on the head to the intake port.

I have a couple though's that might make a difference. I was thinking the small RTV on the Edelbrock gaskets I used that I always installed them up so they seal on the manifold. What if I installed them down to the head's surface. I could the put a really small bead on the gasket side and let it dry completely and the install the intake.
Also I noticed that the gaskets are really narrow at the bottom and could that cause the gasket to creep up with high engine vacuum. I have 17 inches at idle and over 26 inches at times when I'm driving.

 

[pishta]

If its angle problem, youll have to remill the intake, making it even more narrow, and then run a thicker gasket (or raise heads with thicker gasket, losing your copmression) Pull intake and plumb a carpenters level across the heads over the valley, jack up side of car to get a bubble level to center, use a pair of angle finders (the kind that swings like a pocket knife) off the level to determine intake face degree on each side. Take these undisturbed with your intake to machine shop and habe it looked at and corrected.port match it again...bummer!

 

[bobscuda67]

If its angle problem, youll have to remill the intake, making it even more narrow, and then run a thicker gasket (or raise heads with thicker gasket, losing your copmression) Pull intake and plumb a carpenters level across the heads over the valley, jack up side of car to get a bubble level to center, use a pair of angle finders (the kind that swings like a pocket knife) off the level to determine intake face degree on each side. Take these undisturbed with your intake to machine shop and habe it looked at and corrected.port match it again...bummer!

I did determine the angles in post 31, they looked ok to me.

 

[pishta]

Are the heads the same angle? Something read that the intake popped up when the right side bolts were loosened. Even .2 degrees, may prop it up. These manifolds dont bend even under 35 ft/lbs of torque, i broke a commando 4bbl trying to torque it over a 318 block dowel (duh!) :-(
I didnt even see the last page of posts so if repeated a prior post question it was in error.

Something to try if you have the material. Put a screw in schreader valve into a engine hoist plate. Drill a .625 hole and install it. Pull rocker shafts, pushrods and install plate over carb gasket. Pressurize intake to about 15 psi (egr allowing ) and listen for leaks from heads. You should be able to find leak with stethescope. Maybe you have a crack? I found a vacuum leak in a pipe plug doing this along with soapy water. Yours will ge harder if its under intake as expected.