Find the exhaust leak!

[Neal]

I've been chasing and exhaust leak. One of the header flanges moved a bit during final welding and leaks at the bottom. I started with FlePro 1415 gaskets. I decided to switch to some thicker copper gaskets from Summit. You can see how well that worked. :sad::sad: I went back to 1415s and doubled the gasket material on the suspect flange. Seems OK for now. Any thoughts?

 

[Jim Cowden]

Neal

Your flanges must not be flat.
Try to get them flatter.
A large belt sander works.

Jim

 

[Dimi Terleckyj]

Copper gaskets will only work if both surfaces are completely flat and true with each other.

Using thicker gaskets will work in the short term but you will find they will still blow out as they age and will require regular replacement.

The only permanent fix is to machine the mating surfaces to sit flat with each other.

Dimi

 

[Cliff Beer]

Hi Neal, hope you're doing great!

Agree with Jim and Dimi, you must have a header flange which isn't quite flat. As Jim suggests, no need for a machine shop, just put it on a good sized bench belt sander to take off the high spot or two.

Put a little grease on the flange bolts as you're torquing it down - this will help it go down equally and the grease will burn off the first time you get her up to temp - anti-sieze is good. Finally, use some Permatex Form-a-gasket on the flange side of the gasket as this help to fill small voids (don't use on both sides as you might not get the flange off again).

Nice weather we're having in Seattle - perfect for GT40 diving!

 

[Randy V]

I echo much of what the others have said but work the solution slightly differently.

I like the copper gaskets (beaded ones) but I use Permatex Copper or Red High-Temp RTV on both sides to help fill in any voids. I let the RTV "Skin-up" on the gasket for about 20-30 minutes before I install the gasket. Anti-seize of the header-bolt threads. Install the header and lightly snug up the bolts. Let cure for 12-24 hours and then torque them down the rest of the way - this compresses the RTV even tighter around the gaskets.
Now the important part - Heat cycling.
Start the engine and bring up to temp - then shut down.
Re-torque all the bolts.
Repeat the re-tightening of the bolts through the next half-dozen heat-cycles.
Eventually you'll find that you can no longer tighten the bolts any more.

On a couple of my racecars, I eliminated the header gasket altogether as I couldn't find a gasket that was the right size or composition. I just used a bead of the Red High-Temp RTV. Worked like a charm. No leakage.

Good luck!

 

[dave harris]

I second Rany's advice (and method as outlined) - have used High temp RTV exclusively for a long time - works great (just so long as you are not trying to fill a 1/4 inch void!).

Dave

 

[Neal]

Three of the four are very close. The fourth has clearly shifted but doubling up the gasket material seams to have resolved the issue. It's hard to justify cutting and re-welding the pipe as the headers are ceramic coated. I put some miles on this weekend and things look good. Chalk it up to one of those "If I knew what I know now, then" experiences! At this point the focus is on putting on the miles as opposed to watching the patina form in the garage.

 

[Mike]

Your flanges need to start out THICK to reduce the chance of warpage. 3/8 - 1/2" material is recommended. Then, as suggested, the surface needs to be made flat again after welding. This is a MUST. If you don't do this, you will ALWAYS get leaks. Copper gaskets will work well, or so I have heard. I use the red RTV only method, and have done so for YEARS. It works just fine. Also, if the flange is one piece, it should be cut apart into four individual flanges. This will keep them from pushing on each other when the whole thing heats up.

 

[Petty Deh]

One common symptom of car exhaust leak is when your car running poorly, either the check engine light is one or there is an annoying noise when you start the car. First thing to do is to keep the car cool and as it heats up, the metal expands which can close small leaks. Most importantly,check the gaskets. This tends to be the most common cause of leaks.

Btw, visit Troubleshooting Exhaust Problems for diagnosing the leak.

___________________
Autopartswarehouse Car Mods.

 

[Phil]

Neal
I am curious as to why your flanges are tied together. Most of the setups I have encountered are separate flanges, and if there are problems they usually are at the fitup in the collector. I once worked on a GTD that had similar exhausts to yours, they weren't a 180* setup so there was no need for separate flanges. A few minutes on a flat belt sander cured the leak we had, and as has been said the flanges were approx 3/8" thick.
Cheers
Phil

 

[Johan]

I do not use gaskets , just sealer, and have had no trouble. Just be sure the flanges are flat. I have individual header pipes and flanges.