In the continuing saga of trying to get our second 57 Dodge half ton pickup on the road...it looks like we've stalled within sight of the finish line! [img]/forums/images/icons/shocked.gif[/img]
The passenger side exhaust manifold was badly cracked when we got the truck. I discovered the heat riser was stuck closed, which would have concentrated all the hot exhaust on that side; this probably had something to do with the cracks.
I was unable to find a replacement manifold for the 315 Poly V8 from a truck, but found a nice one from a car. After very careful measuring I found the only differences were (1) the heat riser on the truck engine went straight down while that on the car angled back 45 degrees, and (2) the length of the generator bracket was about 1/2" shorter for the car. Neither of these differences bothered me since the riser could be swapped out and I was converting to an alternator anyway so could make the jig for the bracket 1/2" longer.
The first time I put the manifold in place, carefully alternating tightening up the bolts, the manifold cracked in the middle as I tightened up the last one. I did them in the order shown in the manual, and did only half a turn on each before moving on to the next. But it cracked anyway. I removed it and found that the mating surface was not flat. So I had it repaired and machined flat. It seemed to bolt into place just fine, but in the morning I noticed another hairline crack in the same area! [img]/forums/images/icons/mad.gif[/img]
I can't figure this one out. The manifold was pre-heated before being welded, and the cool down also took place in an oven. Could the engine block have been warped by the heat of that stuck riser? If so, how do I deal with it?
I think at this point I'll grind a v-channel into the crack and use some of that POR15 fireseal stuff to repair it. I have nothing to lose and it might just work!
But I sure could use some sage advice at this point! [img]/forums/images/icons/crazy.gif[/img]
<font color="blue">...Could the engine block have been warped by the heat ... </font color>
Hi Pete,
How about using a "straight edge" to test for flatness on the block side prior to rebolting the manifold up...
(to test your theory) [img]/forums/images/icons/wink.gif[/img]
John and Egon -- Thanks for the replies. I've wondered about the gasket material since these had to be cut out by hand from sheets. (Just try finding a gasket for an old poly head that was only made for a couple of years back in the 50's!) I'll do the straight edge thing if I ever take that manifold off again, but I'm hoping to avoid that step.
Also look into a type of gasket material like asbestos, and very flexible that could basically "seal" the manifold without "torquing" to the breaking point...
Pete:
Hope your solution works.
John's got a good idea.
Perhaps back off on the torque to help reduce stress.
Some usless trivia: Many a year ago I was told cast iron gets harder with age as carbon nodules will form over time at the grain boundaries. Now the fellow who said this had also had a bridge he designed fail in the construction phase due to spring runoff.
Ahem, I did the high temp epoxy thing and ran into another speed bump. Since I couldn't find a replacement manifold for the 315 Poly in a truck, I used one for a car. The bottom end that connects with the exhaust pipe is about an inch shorter, so there's a gap between the manifold and the exhaust pipe! [img]/forums/images/icons/blush.gif[/img]
I'm so close!!! But I'll have to tow the beast to another shop to have them finish the job. Heck, might as well replace the entire rusted exhaust system while the old truck is there!
If you're going to tow the truck in, they might be able to deal with the mainfold problem too, or at least give you some ideas on what might be causing the problem.
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