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Preventing Exhaust Manifold Cracks.
https://www.slantsix.org/forum/viewtopic.php?t=9146		 Page 1 of 1
Author:  IMGTX [ Sat Apr 24, 2004 1:17 pm ]
Post subject:  Preventing Exhaust Manifold Cracks.
I had to replace the cracked and busted in three pieces manifold I had.

First I had tried a later model (and more crack resistant) manifold that had the later model choke but it wouldn't work do to the choke.

A generous member of this board gave me an Exhaust Manifold for my 70 Slant Six Barracuda and it was from a 1970 model so everything will fit. unfortunatly I can see the tell tell black lines of two cracks starting in the same spot where my original manifold cracked.

This car is going to be restored and I would like to save this manifold since it is the orignal style and they are getting harder to get.

What can be done to prevent this manifold from cracking farther? Is there a treatment or process that will let this manifold last for ever like the rest of this mighty /six 198 will?

Any ides on how to prevent or save these crack prone manifolds?

Thanks
Author:  steponmebbbboom [ Sat Apr 24, 2004 5:59 pm ]
Post subject: 
You could try shot peening, I guess. The biggest cause of these manifolds cracking is incorrect mounting. Following the instructions listed in the articles section will go a long way to save your manifold. I would add that it is very important to maintain proper valve clearance and fuel mixture, because a lean mix or a tight exhaust valve will make exhaust temperatures soar. I'm actually trying to figure out how to cheaply install an air/fuel gauge to monitor mixture. This is one of the reasons.
Author:  Slant Cecil [ Sat Apr 24, 2004 7:43 pm ]
Post subject: 
Several things can cause it but I believe the #1 reason is the motor running too lean. Most carbs are set up close to lean when new, so a little dirt or grime can lean it out more creating more heat than the manifold can take. Retarded timing and putting a load on it, like trucks tend to do, will aggrevate it more. I think if you remove the jet(s) and drill them to the next letter size bit, usually about .003, it will allow the manifold to live and still get good fuel economy while giving a better running motor. I drilled the jet in my near stock '68 V200, it gets 20mpg+, ran a 18.19@76 last Saturday nite, quicker than most stock slant 6s even with my fat 285lbs in it. Car is all stock except Mopar electonic ign and a 2.25" exhaust.

Cecil
Author:  Marc [ Sun Apr 25, 2004 3:43 pm ]
Post subject: 
I think I caused one to crack by over tightening the bolts. When I got my 65 B'cuda in 1985, I had the engine rebuilt. When I installed the manifolds I used my normal tighten it down and then tighten a little more. The manifold very quickly cracked. I got one from a junkyard and carefully torqued to specs. That manifold has lasted 19 years.

The manifold has to be able to grow and shrink relative to the head so follow the torque specs.
Author:  SlantSixDan [ Sun Apr 25, 2004 10:04 pm ]
Post subject: 
I was looking at an exhaust manifold just yesterday for a late-model Jeep 4.0 Six. What a neat piece...it's made of welded pipework instead of cast iron. Weighs very little, lasts a long time and is inexpensive to replace. The 4.0 does not have an intake/exhaust heat crossover, so that would be one obstacle, but I found myself wondering if it'd be possible to put together a manifold like this for the Slant.
Author:  IMGTX [ Mon Apr 26, 2004 7:40 pm ]
Post subject: 
Thanks guys.

It concerns me about the installation thought though because the I am the second owner of this car and it had no engine work done to it other than flushing plugs and wires when I bought it.

Look like if it were an installation problem then it's ma Mopars fault. HMMMMM wonder it is covered under the warrranty.....LOL.

I will be sure to check the carb since I am in the process of rebuilding it.
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