How to fix a terrible exhaust leak?

Bradbutlernc

Well-known member
I just got the falcon back running today, and she runs awesome, but firing it up at night i noticed a problem. The last cylinder exhaust gasket is leaking so bad, i can see fire going from inside the cylinder down into the exhaust port. The exhaust gasket is newer too, so maybe i have a bigger problem than i think? It looks like about a 1/16 inch gap all the way around the gasket area. Ive read that people use 2 copper exhaust gaskets to fix the problem because the old manifolds warp over time? I didnt see it leaking around the other ports, and the last one is the only one air was coming from. What have you guys done to fix this problem before?


Id like to get one of those exhaust port dividers when i replace the gasket, whats the general opinion on this being a worthy upgrade?


Also, is it normal for actual fire to blow from the exhaust port? Only happens when free revving it and letting off, i assume its a bit rich and thats causing it.
 
8) start by pulling the exhaust manifold and checking it for straightness. sometimes they warp and you get a bad exhaust leak. also check it for cracks. the one on my 64 falcon is cracked in three places.
 
Im pretty sure its warped as none of the others are leaking, what would i have to do about that, call a machine shop?
 
Bradbutlernc":3uivhapk said:
Im pretty sure its warped as none of the others are leaking, what would i have to do about that, call a machine shop?

If it is simply warped it might be possible for a machine shop to true up the face of the manifold to where it will seat properly. If not, then you're probably better off just finding a replacement rather than trying to repair it.

My guess is that somebody here will have one left over from when they switched to headers.
 
The fire is because there is unburned fuel coming from the cylinder. Fresh air is getting sucked in the leak and allowing the extra fuel to finish burning. This is pretty much how a 'smog' pump system worked. Idea was to get a more complete burn (without actually making the engine more efficient) rather than just dump it into the air. As this process happens the temps are increased which is likely causing further damage especially to things like gaskets. It only takes a slight leak to burn out the gaskets. It also does not take much to melt the manifold itself. I had one that just had a slight crack but it let enough air in and got the temps high enough to turn the cast iron so brittle that I could pick out chunks with my bare fingers. This situation was also helped by the fact that the choke was not working (stuck shut) which made even more un burnt fuel available.

The mustang vendors have new manifolds. Under $200 IIRC. Fit was fine and I have had mine for almost 4 years with no issues. First 2 years went on with gaskets and no machine work. Last 2 years no gaskets because I had the head done and at the same time had them surface the manifold. If you have both surfaced they will seal up fine with no gaskets to fail. Having the correct bolts / washers is also critical. Typical hardware store bolts dont allow for the proper expansion and such. There are also some on Ebay for $120 ish. I cant imagine there is more than one place making these so I would think they are the same as the vendors.
 
If it's not cracked or too badly corroded, you may be able to fix it by just torquing it down properly.

On the early cars the repair manual said to start at the center and work your way out when installing the manifold. Not sure when they changed the procedure, but on the later cars the process is to start with the rear and work forward. Try a new gasket and see if that helps.

One mistake is using ordinary bolts and lock washers. Ford developed those "ramp-loc" bolts to prevent the exhaust manifolds from loosening. That might also help.

I wouldn't go to the trouble of adding a port divider to a cast manifold. The center ports just end up dumping into an void in the manifold anyway.
 
When removing the old manifold be careful about those bolts on the ends that go into the little dog ears on the head. It's very easy to break off the rear one.
 
That rear one is already broken off, so is the one on the front. They have big bolts with washers holding them on, seems to be pretty tight but still pisses me off a bit, i dont like broke things. Other than that it looks like all the stock exhaust bolts are there. Who here has tried the 2 gaskets thing?
 
Well, i went and bought 2 exhaust gaskets, and some copper spray gasket maker. I plan on putting copper gasket spray in between the 2, and letting them set together, then putting them on the manifold for extra crush. Anyone have any idea what size collector gasket i need at the flange? Im not sure if its leaking but i wanna get one just incase.
 
Alright, just got done replacing the gasket. I doubled it up, and glued the gaskets together with copper spray gasket maker, which seems to work pretty good. I also put the copper spray on the exhaust manifold/side of gasket too. Fired it up for a few seconds and everythings sealed good EXCEPT the last manifold, its puffing out a tiny bit of exhaust from a little gap back there. Im gonna let it set for 24 hours like its supposed to, then take it for a long drive and come back and retorque the bolts when its hot, maybe thatll help. Overall i did a good job, just that one leak is still present, but nothing at all like it was before. If retorquing the gasket doesnt help, what would you guys try? I think maybe piling some high temp epoxy over/into the gap will fix it, as i dont plan on removing the manifold again anyway. Any other products i can try?
 
If the leak isn't fixed the hot gasses will eventually erode the gasket. I think you may need a new (or milled old) manifold and a fix for those broken ears.
 
I replaced my manifold with a 68 model which is a lot heavier built and also better flowing, I also had a broken ear on the rear cylinder and couldn't stop my leak until I tack welded a bolt to the head. I had the head off at the time for some other repairs which made it a lot easier, I ground a notch for the head of the bolt to catch in so the existing material would take most of the strain instead of the tack weld, granted this might not be easy with the head on the car.
 
Well, my leak is coming from the bottom of the manifold in the rear where there was a low spot in the exhaust manifold, the ear is only partially broken and is holding the bolt just fine, im just using a big washer to hold it on. Right now im replacing the donut gasket which was also leaking, and i measured it to be 1 20/32 in size so hopefully thats right. I gotta go to the parts store again and get new nuts/washers for the manifold because the bolts that were on it were stripped, made of brass :shock:
 
That's actually a very good idea, they won't ever rust and don't really bind either. BMWs come with brass or copper hardware on the whole exhaust.

They can easily hold the 18-20 ft-lbs that they are supposed to be torqued to.
 
Well, doing more testing today i discovered another leak at the front, nothing i can really do about that one. Leaking between the steel side of the gasket and the ex manifold of course. Im going to end up just buying a new manifold or getting a used one and machining it. What are my other options?
 
I wouldn't mess with a used manifold, unless you could get a known good uncracked, unwarped one that hasn't had the center divider / choke tube thingy burned out for little or nothing - and I'd pretty much only trust a board member here for that. A warped manifold can be resurfaced flat again, but if there are ANY cracks or near-cracks in it, it's easy for it to break apart during machining. By the time you buy a used manifold, have it checked for straightness and cracks, do any machining, you could easily spend $100 or more - and have nothing to show.

You can pick up a brand new manifold off ebay for about $75 plus shipping, I believe they come in the 1 3/4" and 2" outlet versions, or is it automatic or manual choke? They use the later (and much better) donut gaskets instead of the earlier flat gaskets.
 
Check both surfaces. Like Jack said an exhaust leak would not only continue to blow out the gasket it will also take material from the head and manifold surfaces.

There is a gasket material that is used for Boilers. It is a very high temp fiber gasket with stainless steal screen sandwiched in the middle. I fixed the Mustang leak at the same spot by using a flat file on both surfaces and then using this type of gasket material.

I did this in a pinch. It did last until I tore it down again to install the headers. With the headers and a new standard gasket it would not seal, as you can see in the pic below. If you can it would be best to remove the manifold and check the surfaces for "flat". Try to do the best job you can the first time.

I also found that the cause was the bad thread in the head. I had to drill through and use a nut and bolt to get enough torque to make it seal. If this is a problem for you as well check out the pic below. Notice I had to make a bushing to make this work. The backside of the head surface is at an angle. You can grind one end of the bushing to match the surface angle of the head and use the other end to provide a flat surface for the nut.

Unfortunately it wasn't enough for the header installation below. You can see where it is blowing out.

ExhaustManifoldLeakNutNBolt.jpg


Good luck, Ric.
 
According to Mike’s website the spec is 20-24 foot pounds for the exhaust. I would be careful about exceeding that. You don't want to strip out the threads in the head.

Good luck, Ric.
 
Take the exhaust manifold to a shop and have it re-surfaced. Go online and order a gasket from Remflex.com. They are pricey but are guaranteed to seal where others wont. They are a very high temp graphite crush style gasket that takes very little bolt torque to adjust. only 17 ft lbs torque.They are over 1/8" thick . I had too many problems with manifold leaks , ready to pull my hair out. Put a Remflex gasket on and have never had a problem since. The spacer between the nut and exhaust gland is also a good idea that I did with my donut gasket also to get more torque against the donut gasket to keep it sealed tight.
 
Back
Top