Bbk 351w swap headers leak - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 13 Old 06-07-2019, 05:56 PM Thread Starter
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Bbk 351w swap headers leak

Anyone else running bbks 351w swap headers and had issues getting them to seal properly at the flanges at the head? I've tried two different sets of aluminum gaskets with horrible results. Leaks on both sides. One set was a Percy's dead soft rectangle gasket that mostly sealed and but in a few areas. I figured they leaked cause the ports on the headers are oval port.
The latest set was a Mr gasket ultra seal gasket that leaked like crazy on both sides, they are oval like the headers. I just ordered some of bbks gaskets supposedly made for these headers. I'm getting really tired of exhaust leaks.


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post #2 of 13 Old 06-07-2019, 07:30 PM
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The bbk stuff I bought 15 years ago when I was a teenager was ok in quality.

The bbk stuff I’ve bought in recent years has been great as far as fit, finish, and quality. I think they do a good job of kicking out nice bolt on mustang products.

Maybe some copper Rtv would help. If you think they’re warped or something I bet they’d replace them.

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post #3 of 13 Old 06-07-2019, 08:43 PM Thread Starter
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Bought them used years ago off a guy on here. Sat in the corner of the basement while I collected parts to build my engine. They may very well be warped, didnt think to check it before slapping it all together. Not sure if I've got enough room in the engine bay to check them while pulled away from the head. They fit around the bellhoising and steering shaft well but not much movement available to do much with them as far as checking them without pulling them again. If I have to pull them again I'll probably just buy some big tube midlength headers. I may end up trying either high temp red rtv or the copper rtv with the new gaskets coming in the mail now.

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post #4 of 13 Old 06-07-2019, 08:46 PM Thread Starter
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Wasnt sure if I'm the only one ever to have issue with these headers sealing. The ports are so big on the headers that there is literally only 1/16"-1/8" of flange material between the port and the bolt holes on each side.

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post #5 of 13 Old 06-07-2019, 09:13 PM
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Are they warped? We've had good luck having exhaust headers platen sanded to get them flat. Failing that, check out Remflex, they make thick gaskets that squish as much as an 1/16" for this type of problem.
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post #6 of 13 Old 06-07-2019, 09:34 PM
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Hi temp RTV (red). You put a bead of the RTV around the ports (either head or header) , assemble them FINGER TIGHT ONLY, let set for 24hrs , THEN you torque to spec. Works every time.
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post #7 of 13 Old 06-13-2019, 01:22 PM
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I had to stack two gaskets for my bbk 351w swap shorty headers. Not sure the brand, one set I had on the car when I took it apart, the other gaskets are the generic engine tech brand I believe. No issues with leaking anymore.

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post #8 of 13 Old 06-13-2019, 02:37 PM
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Remflex with copper rtv

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post #9 of 13 Old 06-13-2019, 10:44 PM
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Ive had the same problem. The bolts back out of the head all the time. I check them often. I hear the cooper is the way to go. If i have to pull them again i also will replace them. I think they would seal better if they were built with a 3/8 flange. And getting those 5/16 bolts to thread in the head without the flange is a pain in the as#.
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post #10 of 13 Old 06-19-2019, 03:16 PM Thread Starter
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Update on this issue. Bought some bbk gaskets made just for these headers. First set came and opened them up. One gasket had a crack between one of the bolt holes and the port. Had to contact the vendor and get another set sent out. New set looked good. Installed them dry cause they're the graphite type gasket with steel insert. Stuck my shop vac up the tailpipe (blowing air, yes I cleaned it out well. Lol) and had several very small bubbles coming from around a couple flange bolts on the drivers side and one leak pretty bad from the 2nd to last bolt on the passenger side. I'm about to throw these away. Contacted bbk today and got the idk let me ask around and I'll get back to you deal. Can high temp rtv be used with graphite gaskets? That's about all I can think of doing. It blows cause the car is ready to roll other than this issue and it's being a pain in the ass.

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post #11 of 13 Old 06-19-2019, 04:18 PM Thread Starter
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Bbk rep called me back and after talking to him hes sending me out another pair of gaskets free of charge to try doubling them up. Hopefully 4th times a charm cause third didnt do it. Lol
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post #12 of 13 Old 06-20-2019, 11:04 AM
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I used a 1487 gasket with copper RTV. No leaks.

Headers were homemade and "flattened" on a belt sander. I used the wider bolt pattern on the flange so avoid the issues of the really thin portion between the port and bolt hole.

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post #13 of 13 Old 06-20-2019, 11:51 AM
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The best RTV I have found is Versachem 88839 High Temperature Mega Copper Silicone.
It actually held crummy Flowtech headers that were warped about .15 inches for one full pass. I install it by letting it partly set up barely tight for a few hours, then torque it down. It can also seal bolts for leaks, although I prefer to use the correct washer under the bolt head if I have that type of issue.

If I were you I would check flange flatness and inspect the welds with a bright LED flashlight for pin holes and cracks. If the header flange is not flat and does not have reasonable metal between the port and outside, you are going to have a hard time making and seal last.

I also recess the flange away from the head between ports, making the flange thin enough to bend and allow each cylinder to seal by its own bolts.

I sure wouldn't stack two gaskets. I already don't like to use even one gasket, although I have heard very good things about Remflex gaskets in turbo applications....and that is far more taxing than your application!!


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