Ok...So I'm tired of searching for answers from my out of touch co-workers. How do you frickin crack an iron cast exhaust manifold? I have only 53,000 original miles on a straight 6 - 223 Ford engine... For thrills, I've replaced the original muffler with a cherry bomb, and it dumps staight out, right after the manifold... I've taken it maybe 30 miles straight 4 times, to work and back two days in a row last week, before the wife climbed my shit for riding dirty...(no inspection) Noticed on the way into work on day two, she was gurgling fuel and backfiring a little when I let off the gas at about 65mph...Just figured some tuning on the carb should adjust for it, but didn't notice it getting any better on the way home. Took it out again this weekend, still dirty, just to have some fun with my kid, and still seemed a little rich when backing off the acceleration. Parked her and let her cool. Went to move her into the garage a while later and fired her up to hear the exhaust bellowing from the engine instead of just under the seat. Sure enough, to my suprise, that sombitch is cracked... WTF?
If the mixture was way off (rich OR lean), your exhaust temp could have been very high. As long as you're pumping heat out, it would be ok. The short dump may have let cold air back to the manifold too fast causing thermal shock.
probably had a sand inclusion in the casting to begin with..or a fine crack in the edge of the casting..
In changing the muffler you changed how the exhaust pipe puts force into the exhaust manifold. Maybe it's hanging more weight on the manifold, or less weight, or is twisting somehow. Whatever you did allowed an existing flaw to grow by restraining the casting differently than it was restrained during the last thousand heat/cool cycles.
Take it off and shoot some pictures of the fracture..see if there was rust already starting in a part of the crack..or if it went all at once.
And for what it's worth. The newer (60's on) Ford straight sixes do have a bit of history for cracking exhaust manifolds.
First, thank you all for the input...Now, if I get a second hand manifold from a fellow hamber, how do I avoid the next one from breaking prematurely?
I just sold a 223 to a guy in Orange County... He took the intake and exhaust off. If you are interested I can hook you up with his email addy... - Joe
I have supported the muffler by moving the original bracket up on the frame...Just lucky there was a bolt hole in the frame, at axactly the right point...
Pretty common occurance really. We see it regularly on company trucks, Fords and GMC's. On the 302 Ford in my 46 I had a tick I took to be an exhaust leak. When the manifold came off it was in two pieces. Joe
I wonder if you had to spread it to get the bolt holes lined up? I've cracked a few SBC exhaust manifolds wfter spreading them (then running them), before I was told to open the holes up. I'd think the same might apply to an L6 intake manifold too?
A lot of times when using used exhaust manifolds, you have to spread them to get the holes to line up so you can bolt them in. I was just wondering (since the intake bolts right up to and near the exhaust on the head) if you had to do the same thing...but obviously not if you're asking what I'm babbling about
Why not just braze it with a brass rod? If it goes all the way around braze what you can then take it off and finish the braze job I had to do this on a falcon and it works just fine.
Cracking of the exhaust is usually caused by unburned fuel in the cylinders still burning in exhaust,sometimes caused by retarded timing or dist problems causing hi exhaust gas temp.
Also make sure its evenly torqued. That will not let it move around while heating and cooling...........
Like someone mentioned above, open up the holes on the replacement unit. Allows them to move around a bit.
Typically the ends of the manifold and the top bolts are easier to get to, therefore they get overtightened, while the ones in the center and under do not. Also these manifolds warp, as they all do. Flatten the next one with a belt sander and torque it equally.
All the advice you've gotten about how to successfully run an old manifold is good advice. But also remember you're dealing with a 40 year old exhaust casting that's been heat cycled a sh*tload of times, so to some extent they're all a roll of the dice. If this new manifold has frozen/busted studs, heat the manifold cherry red with a torch and crank em out with vise grips. good luck
Old guy I know told me to put a very thin layer of antisieze around each port and start in the center and work the bolts down slow & easy also antisieze the bolts after wire wheelin if they are old or buy new if your $$$. This has not failed me on 3-4 different engines w/ old iron manifolds! Must have something to it?
Oh man I feel your pain. I bought my Plymouth with a cracked manifold. I've been trying since April to remedy the situation. Long story not worth telling. Short answer, could've been impurities when it was cast. If you do decide to braze it, make sure you do as much as you can with the manifold on the block. Heated mine, welded it off of the car, went to put it back on and it's now too short. Bad juju. I'm thinking of making headers.
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