IH345 Aluminum Intake Manifold Leak

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IHCScout78

Member
I put an aluminum intake on a 345 during a rebuild. 3 coats of permatex copper on a shim gasket, hylomar on the bolt threads, torqued to spec per pattern, at least for the bolts I could get a torque wrench on:icon_eek:

it has developed a noticeable coolant leak on both sides of the throttle boddy. Coolant is pooling between the intake runners on top of the manifold. Bolts seem tight with a wrench; can't get in there with a torque wrench without some dissassembly.

I also have some coolant on the valley pan cover where the pvc oil normally puddles:smile5:

I have never had a leaky intake manifold on the cast iron monster IH used before. Has anyone seen this on the aluminum intake?
 
I've never heard of any issues. I've also installed a couple my self, never had an issue.
I would guess you have not crushed the steel gasket enough yet to properly seat it.
 
I haven't installed an aluminum manifold on a vehicle before but on the all aircraft I've worked on hylomar works great on gaskets but we would use permatex aviation form a gasket on the bolts. Especially bolts that penetrate coolant or oil passages, which I did when I reinstalled my cast iron manifold. Danny
 
On aluminum manifolds you must re-torque After the first start up, warm up to temperature.
Following the prescribed torque sequence is also very important.
You can't just plop it on there, torque some, wrench some willy nilly and treat it like cast iron.
It doesn't matter if it's IH, gmc, toyota or suzuki, it's gonna leak if not done properly.
All you can do now is take it apart, check it very carefully for warping and cracks.
If it checks out, use new gaskets and try again.
 
He did say in the first post that he torqued it down to spec in pattern.

For the bolts you couldn't get a torque wrench on, how long was the hand wrench you were using? If it was short maybe you weren't getting those as tight as you thought. Try turning the bolts installed with the torque-wrench with your hand wrench for comparison.

Did you clean up the holes and bolt threads with a tap and die set?

I've never seen this with sv heads, but some heads if cracked will leak coolant at the manifold.

Forgot to mention. You also need to check that everything is flat with a straight edge.
 
Not really interested in getting into a pissing match with ya, I was only pointing out that he didn't just plop it on there in a willy nilly manner. Interestingly enough I have half a dozen edelbrock intake instruction sheets and not one specifies re-torquing. Yes, alum. Intake bolts are somewhat prone to coming loose, but not with a steel shim gasket. His root problem is going to be something else other than a lack of re-torquing. Btw ihcscout78, steel shim gaskets are not the best choice for an alum. Intake.
 
Yes on using something other than steel gaskets. Iirc the steel will react with the aluminum and erode the gasket.

Old timer note. Way way back when offenhauser started making aluminum heads, yes flat heads, the gaskets would fail in no time flat. The solution for the problem I was told (I'm not that old) was to coat the gasket with peptobismol to prevent the acids from forming and eating the gasket.
 
Hmmm, by any chance during the rebuild, did you take any healthy cuts off the block? I decked the crap out of the 351 in my 69 mach I, and then had to have the intake manifold cut to match.
 
A lot of good points have been brought up. Not all are potential causes for the op's problem, leakage..
1) steel shim gaskets should not be used between aluminum and steel.
A. The first problem is not initial sealing (which will be fine initialy if properly coated and compressed) but the fact that the two dissimilar metals create a small current that corrodes the interface. The correct term in galvanic corrosion.. Only composite and stainless steel faced gaskets.
B. The second problem is that the aluminum has a larger cte ( coefficient of thermal expansion) than the steel. This creates a wiping of the aluminum across the steel gasket ribs with each heat cycle. This leads to wearing of the aluminum and fretting corrosion at the interface.

2) the retorque requirement is a function of the gasket relaxing after the first few heat cycles. Aluminum will cause a bit more of this due to it moving more. Only composite gaskets will relax, the steel shim type will not once compressed and yielded. On a personal note I always recheck fasteners after a build is first run. More to double check than anything. A proper retorque requires that the bolt be backed up about 1/8 and brought back up to the recommended torque.

3) the aluminum manifold is 3 times more flexible then the iron monsters. That means the bolt locations will not share much clamping force with each other. Each location needs to be properly tightened to ensure the areas between two adjacent bolts is clamped properly. Composite gaskets are way more forgiving due to the compressable nature of them.

For torqueing hard to reach bolts I use a fish scale and a long pattern box end wrench. Hook the scale to the wrench 12" from the center of the box end. The pull force must be tangent to the wrenchs swing arc.
 
To prevent galvanic corrosion between two dissimilar metals, you can use a product called eck.

Eck comes in aerosol spray cans and liquid-paste in cans or tubes.

You can google it.... Or -> www.eckcorrosion.com
 
Just came across this.. I just ordered a set of manifold gaskets from ihparts but no where was it listed to specify if you were using an iron or aluminum manifold. Am I to assume that I will be receiving steel gaskets which is not recommended for my setup (aluminum intake)? I've never paid attention to dissimilar metal corrosion but to be honest I often forget that my intake is aluminum.
 
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