Exhaust gasket leak

[bball7754]

I replaced the exhaust gasket on the rear cylinder of my Crossflow last weekend. Used some high temp silicone between the gasket and block, but didn't use it on the side of the header flange.

 

Fired it up last night to bring the engine up to temp and retighten, and it still leaks. Got better after I tightened, but still not a complete seal.

 

Realized that I hadn't cleaned the surface of the header flange, only the surface on the block, so I'm wondering whether that's causing the problem.

 

Long intro to the real question. I have a track weekend this Sat. and Sunday. Any chance for real damage (burned valve,??) if I leave it as is? I've considered taking it apart and cleaning up the surfaces, but am worried that the gasket won't make it through the process, and I don't have another replacement.

 

Steve

[TheDingo8MyBaby]

Why not just clean it up and try again? You've got plenty of gasket material. Exhaust gaskets on the crossflow are notorious for leaking... You can also buy a gasket for a 72 ford pinto if the permatex doesn't work.

 

Can't say for sure you won't burn a valve, but it isn't likely- at least not with a small leak. You might lose a small amount of power as well.

[Dave W]

Before you put the exhaust back on. Take a straight edge and check to see if the mounting surface on the manifold or header is flat. You may have to level the surface to get a good seal. You can also try putting Permatex 300 on the gasket.

 

Dave W

[MHKflyer52]

If it is leaking enough for you to know it then you should reseal the header flange to head. If the engine sucks cold air back on to the hot valves it can cause a cracked valve or even a cracked head in the exhaust port and cause the water jacket to leak or be pressurized from the exhaust gasses. This is what happened on my original engine due to the exhaust flange bolts backing off enough to cause a leak. If you want to see some photos go to this link of mine and look closely at the exhaust ports.

http://picasaweb.google.com/MHKflyer52/OverheatingProblemBeingSolvedByReplacingEngine#

Hope this helps.

[bball7754]

Martin - That does help, although it means I may have to write off the track day.

 

Dave - I didn't use the Permatex 300, but did dress the one side of the gasket with Permatex High-Temp Red RTV Silicone Gasket. After I scraped the block surface with a razor, I used some steel wool to get the remaining old silicone off. At the time I wondered whether the steel wool would cause the surface to become untrue - although obviously I decided to go forward with that method. Bad decision?

[MHKflyer52]

At the time I wondered whether the steel wool would cause the surface to become untrue - although obviously I decided to go forward with that method. Bad decision?

 

What I was trying to say in a nice round-about way that you need to reseal your exhaust to the head and giving you some info to help you make that choice as I feel that I can only suggest what to do and do not like to tell someone that they have to do something unless it is a safety thing.

I do not think the steel wool will or can cause the face of the head to change enough to cause a leak like you have talked about but maybe it can...I would suspect that the exhaust manifold flange is warped due to the heat it see's. I would replace the gasket (most exhaust gaskets are onetime use) and use a good high temp sealant on both sides of the gasket and tighten the bolts down in an even manner so as not to bend the exhaust flange and work from the center bolts / studs out to the ends of the flange.

You should be able to fix this and still make your track day I would suspect.

[slomove]

Don't know anything of the Crossflow special needs....

but on my Zetec I am not using any exhaust gasket at all, only a thin film of the red Permatex stuff. When I had the car worked on by MSI several years ago they ground the header flange to an even plane and said no gasket needed. Well, no problems so far...When I have to re-install the headers nowadays I just brush/scrape off the old silicone, apply a new silicone film and bolt down the exhaust.

[bball7754]

Here's the update, for those of you on the edge of your seat.

 

First, a bit more background. My Crossflow actually has 3 separate gaskets, one for the front cylinder, one for the middle two, and one for the back cylinder. I had replaced the rear cylinder gasket about a year ago. The photo is a bit blurry, but shows the setup.

 

To pull the header off, I have to remove the muffler from the 4-1 collector, then remove the collector.

 

Anyway, did all that (again), and pulled the rear header off. As hoped, the gasket stayed mounted to the block from the silicone gasket stuff I'd used. Pulled the header out to check the face of the flange, and realized immediately that when I'd replaced it previously I'd noticed that the header pipe was slightly proud of the flange face on one side. I was able to use a round file to bring down the pipe without touching the flange face.

 

Put the Permatex silicone gasket stuff on the flange side of the gasket, then put it all back togther. Let it set for about 30 minutes, than fired it up.

 

No leak. Brought it up to temp and re-tightened, and still no leak. I think I'm good to go.

 

Thanks again for all the feedback.

[Kitcat]

Dumb question: How do you know if your exhaust gasket is leaking? In the driver's seat of my Crossflow there frequently is an exotic cocktail of smells: exhaust blow-back, carburetor blow-by, evaporating engine crude, etc., etc. Can you feel it with your fingers, do you need to rev the engine?

 

Mike

[lowflyer]

The flange on the header is often the cause for an exhaust leak.

 

While it's a hassle, next time you take the header off use a steel straightedge to check the mate surface for being flat.

 

I ended up using a belt sander on mine to get it close.