CRACKED EXHAUST MANIFOLD

[fryedaddy]

I have got 2 cracked manifolds on my 73 f250, 360 ,4 speed.my friend at the muffler shop said he would fix them,i have a good set to put on,BUT he said i had to put new motor mounts on or they would break again.i was wondering if that is the case.the motor mounts are old and cracked,but not broke,is motor mounts usually he problem,or are the exhaust manifolds  just bad to crack?

[Rory428]

I also had exhaust manifolds crack on my 74 F350, I had 2 rights and 1 left crack in a 2 year period, when hauling heavy loads. Installed a set of headers, and never had another issue. I really fail to see how motor mount issues could possibly contribute to the cracking of the exhaust manifolds. Even if the mounts were both completely broken, and allowed the engine to flop all over the place, I could see that potentially causing stress on the front exhaust pipes, but not to the manifolds themselves. Also wonder how long welding up cracks on the old exhaust manifolds would hold up.

[GerryP]

...Also wonder how long welding up cracks on the old exhaust manifolds would hold up.

Depends upon the welder's skill level.  Brazing is normally the method used to repair iron manifolds.

[cleandan]

If you want to weld the manifolds it can be done very nicely with NiFE rods (Nickle iron)
There are a few different brands and names out there but I suggest you visit your local welding supply house (if you have one) and see what the offer.

The process of cleaning, prepping, pre-heating, welding, cool down and some peening is particular, but if you want to try you can get there in your garage.

As far as the manifolds cracking are concerned there are some things to look into.

Now true are the heads at the manifold mount?
How true are the manifolds at the head mount?
Are you using a gasket...especially if it is one of the thick styles?
Are the mounting bolts tight, and staying tight?
How hard, and for how long, are you heating the manifolds and then what have you done for cool down.
How rusty/pitted are the manifolds?

There are many things, both reasonable and not so much, that can cause manifolds to crack.
Look into this, and figure things out, prior to installing another set of manifolds otherwise you may be changing them again sooner than expected.