Fixing a pernicious exhaust leak (help!)
 

So, I have a Nameless 2.5" fp/op combo pipe connected to a @JDLAutoDesigns UEL header. I have a brand new Subaru OEM gasket between them and the bolts tightened appropriately. A feel test and sound test so far reveal no leaks, but logs and a smoke test show a small leak. This is the second gasket I've tried (I've not gone double gasket b/c of the increased risk of leaks), and still gotten the leak.

So, does anyone know where I can get a thicker gasket to put between the OP and header? The OEM gasket apparently is too thin.

JDL or @Ryan@Nameless, do either of y'all have replacement exhaust gaskets that are thicker than OEM for your exhaust components? Or any other trick to seal the leak I'm getting? The leak is enough to cause some odd lean spots in the tune that simply cannot be tuned out.

Thanks, folks!

I know nameless has a thick graphite gasket they use. I believe it's made out of Remflex. You can probably find what you're looking for on their site. http://www.remflex.com

Worst case scenario they sell plain sheets so you can cut your own. http://catalog.remflex.com/COLLECTOR..._p/gs16511.htm

Looks like I need to give nameless a call and see if they'll send me a 2.5" 2 bolt gasket for the header to overpipe flange connection.

Just curious here, where does an exhaust leak show up in logs? What are you using to log data?

You'd have to ask @nelsmar how he could tell something was off, as that's how we do tuning when he's not in the car tuning it himself (I log, and save the logs to a folder connected with dropbox, and he gets the log and issues a new ROM in the dropbox folder, which I then flash).

I log with EcuTek.

Assuming everything is mounted and lined up properly, tiny elusive leaks like this are most often caused by an irregularity in, on or between the mating surfaces, e.g. warping / distortion, surface damage, dirt, flash, or an edge burr. It doesn't take much of a gouge in a flange surface or bolt hole edge to prevent complete sealing. And overtightening the flange bolts even once can warp it.

The first thing I do when I have a tiny, hard-to-seal exhaust leak is to separate all mating surfaces and parts, clean them thoroughly, and inspect / measure them. To check flanges for flatness, place them against a thick glass surface or steel straightedge and see if a thin piece of paper is held firmly between the two. Any minor deviation from roundness will have the same effect on a slip joint. Machinist's indicating dye will tell you if mating is complete between flat surfaces, and absence of dye transfer to the dry surface will locate any gaps for you - but doing this takes patience and great care. Very slight warp in an exhaust flange can be corrected by rubbing the surface against a thick glass slab coated with valve grinding compound until it's flat again. More than that will require milling (and a thicker gasket if there's no slip joint or other way to advance the pieces toward each other while fully on the mounts) or replacing the flange.

Assuming the parts are OK, a thicker gasket is a sounder approach than gooping up the joint. But the quick and dirty fix is copper ultra RTV or Hylomar EAP5 (both of which work well and are more durable than I thought they'd be - I have friends with header flanges sealed with copper RTV that lasted for years).

Still and all, if the parts were designed to mate well with one gasket and they do so on everyone else's car, something's wrong. It's best to find and fix the problem.

Yeah, I don't want to take off the header for checking these things. Need a quick and dirty but effective fix.

I think it could be minor imperfections, honestly. A good gasket should seal against those, though I'd think.

The parts mate up well with one gasket, and you can't tell by feel that there's a leak. The only ways that indicate that it's there is the sound of one intermittently (after several heat cycles and high rev pulls), data logs with odd lean spots and other indicators, and the smoke test showing a very small, very wispy (not at all thick and streaming) strand of smoke sneaking out.

Well.........both Hylomar (the one for exhausts, not the regular blue one) and Ultra RTV have worked out fine on headers at the track when a Q&D was unavoidable, and I do know of at least a few cars that have run for more than 3 years with the same compounded header gaskets and flange gaskets. At the very least, it'll reduce your risk of CO2 narcosis!

Where does one get this stuff? NAPA, O'Reilly's, AutoZone, or some place more specialized?

Copper RTV is available at any auto parts store. I've had a tube of this Permatex version in my trailer and my emergency repair kits for years:

http://www.all-spec.com/images/produ...atex/81878.jpg

I'm not sure where (or even if) you'll find Hylomar exhaust assembly paste in the Desert Metropolis - you'll probably have to order it on line if you want to use it. I think it's a better choice because it's made for initial assembly rather than repair - it's more adhesive, and it's got slightly better temperature resistance.

I can't seem to find it available (the exhaust compound, not the blue stuff) except in the UK. Amazon.uk sells it, but not regular US amazon. I'm going to pick up the copper RTV stuff. Sound like it works well, too.

So I basically apply the stuff to the flange edges on both pieces, place the gasket, and tighten down to "guttentight" :bonk: ?

it should say on the package but do not torque it down right away. I am going from memory, but I believe you apply, then let it set up for 5 minutes, then assemble it, but just thread the nuts/bolts finger tight, this will keep the copper gasket from just getting squeezed out. Wait 12/24 hours (whatever the package sais).. then come back and torque it down. Did this with a rusted flange I tried to sand back down flat, used the copper gasket inbetween flange and 2 other gaskets, and never had a problem again.

cant wait that long, as this is my dd.

Man, have I been there before! Do it as soon as you get home, tighten the bolts up the next morning, and you'll be fine when you head out again. I've given up a lot of sleep and almost as much skin in the last 50 years to make things like this happen, and I'm sure my family didn't miss me that much at the dinner table.

Just remember that anybody can steer the ship when the sea is calm, but greatness rises in a tide of adversity. This is why God made Kevlar mechanics' gloves.....

http://ecx.images-amazon.com/images/I/418LHMgncGL.jpg