All Big Six Intake manifold gasket weird leak - ideas? UPDATED 1/16

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cornfarmer

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(I'm going to try to describe this first because it's dark/cold and I can't get a good photo right now)

This is a brand new Victor Reinz gasket that was installed a couple of months ago. The metal / perforated part of the gasket has a ripple or raised crease in it - see my cheesy diagram below showing the ripple in red and a pic of it below it - it's definitely a noticible leak i.e. it sounds like an exhaust leak, and I checked/torqued the exhaust bolts to make sure they were all fine. Looking at the pic, I'm not sure what might have happened. It kind of looks like the edge of the port cutout might have inadvertedly gotten enlarged downward when tightening the stud? Then when the temps dropped a bit more for fall, the wider change in temps caused the wrinkle? This only started happening a couple weeks ago.

Short of redoing the whole dxxn thing, are there any tricks I can try to fix this before I tear it down all over again? Slap a thick coat of RTV or JB Weld on it? Is there a way to smoosh it down and smooth it out, etc.?

Spitballin' here....

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Edit - photo of actual area:

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cornfarmer

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So if anybody cares, doing some research online I found some hearsay that these manifolds never had gaskets installed originally. Only that if they were removed they could warp and then gaskets became necessary.

So I'm looking into getting it resurfaced and then putting in a Remflex gasket. I think that should do the trick.
 

THE FRENCHTOWN FLYER

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I think it probably never sealed completely. The small leakage of hot gasses gradually eroded the gasket, became larger, and ultimatey distorted the metal matrix (a la the space shuttle O-ring disaster).

While some Ford engines were intentionally assembled without exhaust manifold gaskets to aid catalytic converter light-off times I have never disassembled a 300 that did not have gaskets.
 

hodaka100

Well-known member
I don't think there is any easy fix. Redo and check the the manifolds for straightness / have the surface milled flat. On "V" engines I use high temp RTV instead of exhaust manifold gaskets so there is nothing thick enough to blow out but I don't think that would be an option on this long engine with the bolts shared to the intake. Has anyone tried it?
 
In my opinion the thick gasket allows too much movement and puts aluminum intakes, particularly the EFI lower, in danger of breaking tabs so I always use the thin paper gasket on the intake and RTV on the exhaust. If a manifold is very far out of flat I resurface it on a flat surface with sandpaper, doesn't need to be perfect, just close enough that the bolts can pull it down well enough. I have never had manifold leaks when doing it this way. Sample size is only around 5 though.
 

hodaka100

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In my opinion the thick gasket allows too much movement and puts aluminum intakes, particularly the EFI lower, in danger of breaking tabs so I always use the thin paper gasket on the intake and RTV on the exhaust. If a manifold is very far out of flat I resurface it on a flat surface with sandpaper, doesn't need to be perfect, just close enough that the bolts can pull it down well enough. I have never had manifold leaks when doing it this way. Sample size is only around 5 though.
Thanks, Good to know... When I did my efi gaskets I did everything as instructed but at some point afterward the rear tab on the lower intake broke. In the future I'll not follow the instructions and just do what I think is best.
 

THE FRENCHTOWN FLYER

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I never did like the fact that the rear tab is the only positive attachment device on the intake. It is too easy to use the bolt that holds it to support the intake while installing it. I think that is when the damage is done - upon assembly, not during use. Based on all the tabs I've welded back on it is a common problem.
On the plus side, finding a used one at a flea market with a broken tang usually means the price becomes more negotiable due to the repair needed to make it functional again.
 

cornfarmer

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Happy New Year BUMP!

Time and weather permitted getting the manifold off finally. I guess we found out why the gasket blew. Looking at the ports in the picture below - at #1 you can see the spacing between them versus the spacing at #2 which have obviously shifted to the right. We put a straight edge on them too and we definately could see that the right side ones were not straight/flush. Enough that makes us think resurfacing it might be a waste of time, i.e. possibly replacing it altogether.

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Is this normal though? (below pic) I noticed that there is a slight rise looking at it from the back.

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Comparing it to this one on ebay, image search, etc. it looks the same as others out there, I was just worried that this was more evidence of warping. (I am probably wrong but just wanted to make sure)

When we test fitted the Remflex gasket, it has plenty of meat that might take up the slack, but it's not perfect so I'm just not sure. Do you guys think a new manifold is the right move? I'm leaning that way.
 

sixtseventwo4d

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The way your manifold has warped is common. The easiest, least expensive repair than I have done that works, at least until the manifold warps so much that you can't get it to cover the port is to have them milled flat while still bolted together as an assembly. Take your manifold gasket and remove the attached intake material layer leaving only the steel reinforced part. Apply a 1/8-3/16 bead of rtv around the intake ports of the gasket; I only apply the RTV to the manifold side of the gasket. Bolt it up and torque is as you would normally. Proper washers help greatly with the longevity. I have done several of these repairs over the years and while it may not sound agreeable, it works. Aside from this, replacement is your next best solution.
 

THE FRENCHTOWN FLYER

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Hi Frank.
Do this: Measure the distance from port-to-port of both the intake and the exhaust manifolds. It should be exactly 4.480", the same as the bore spacing. I am guessing the exhaust manifold shrank to the left, not the intake moving to the right. It is a common problem for the exhaust manifolds to shrink, since the heating/cooling cycle is much greater than the intake. Measuring will confirm which moved the most.
The intake is supposed to be "bent" like that. Note the short runners are also exiting the log at different angles. This becomes quite the bugaboo when trying to modify or build intakes from scratch.
 

cornfarmer

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The way your manifold has warped is common. The easiest, least expensive repair than I have done that works, at least until the manifold warps so much that you can't get it to cover the port is to have them milled flat while still bolted together as an assembly. Take your manifold gasket and remove the attached intake material layer leaving only the steel reinforced part. Apply a 1/8-3/16 bead of rtv around the intake ports of the gasket; I only apply the RTV to the manifold side of the gasket. Bolt it up and torque is as you would normally. Proper washers help greatly with the longevity. I have done several of these repairs over the years and while it may not sound agreeable, it works. Aside from this, replacement is your next best solution.


Thanks for this - I've only got one machine shop in my area that can probably do it - what's a general ballpark price on getting it milled? The new one on eBay doesn't necessarily break the bank, but having options is always good.
 

sixtseventwo4d

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I think your greater concern might be how quickly you can get them to do it.
Thanks for this - I've only got one machine shop in my area that can probably do it - what's a general ballpark price on getting it milled? The new one on eBay doesn't necessarily break the bank, but having options is always good.
 

THE FRENCHTOWN FLYER

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Thanks for this - I've only got one machine shop in my area that can probably do it - what's a general ballpark price on getting it milled? The new one on eBay doesn't necessarily break the bank, but having options is always good.
See if you can find a shop with a large belt sander / re-surfacer. One shop in my town has one. They even resurface heads with it.
 

bubba22349

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You could maybe try loosening up the three bolts holding the exhaust manifold to the center of intake manifold than set the them on a good flat surface to line them up before retightening them. You might also replace that center gasket while you gave it apart too. Best of luck
 

cornfarmer

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You could maybe try loosening up the three bolts holding the exhaust manifold to the center of intake manifold than set the them on a good flat surface to line them up before retightening them. You might also replace that center gasket while you gave it apart too. Best of luck

That's a good idea, thank you.
 

cornfarmer

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Follow up question - depending on if we go with a new intake or even go nuclear and replace the exhaust manifold too - I fear snapping the original bolts, or reusing them. Anyone know the bolt specs in case we need to replace one or all of them?
 

cornfarmer

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So we took apart the intake/exhaust halves today - and probably no surprise to anyone here: when we put the metal straight edge on either of the manifolds while separated, the ports are straight and level. The intake just won't line up straight when they're married. I think the warp is some kind of back to front twist. If we tried the trick above, where we bolt them both onto the block first, then tighten the intake/exh connecting bolts second - when tightening, I think the tweaked intake ports on the right would just go back to their misaligned, leaky position.

Anyway, I'm getting the new intake from eBay and hopefully it will line up and work. We shall see.
 
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