The Stovebolt Site Forums The Parking Lot Big Bolts 'More fun' with the 59 GMC 503 exhaust

I managed to get the manifold flange detached from the manifold by cutting the bolt/nut ends off with a metal cutting disc, then loosening the bolt shafts by wrenching the bolt heads....not easy or fun....to get to the inside bolt I had to squeezle under the truck and reach up alongside the engine block. I then discovered that my acrobatics were unnecessary, since the inside flange ear of the manifold was cracked right off.... I then looked closer and found that the rear/outside ear was almost cracked through, leaving only one good ear of three. I can tell that someone long ago had had this apart because the jam nuts on the flange bolts are not all the same. This leads me to believe that someone tightened the connection way too much AND/OR the GMC engineers made a little goof in deciding how thick to make the cast flange ears. What to do now? Removing the rear portion of the exh manifold is a possibility, and weld it, but something tells me that cast weld would not hold up to the retightening.

Remove the manifold piece with what's left of the output flange on it, and have a machinist fabricate a flange from steel, not cast iron. Then mill the remaining ear off the manifold and weld the steel flange onto it. Welding steel to cast iron is tricky, but it's doable. You'll need to find an oldtimer who knows how to use nickel-alloy welding rod, preheat, weld, post-heat, peen, and slow cool the weld in a pile of sand to prevent the weld from cracking. Once a few passes of nickel rod are in place, you can build up a thicker weld bead with 6011, 7014, or some other general purpose steel rod. The mild steel welding rod will bond to the nickel alloy without concerns for cracking, as long as it doesn't overlap onto the cast iron. I learned that trick from an oldtime welder/pipefitter when I was a maintenamce man at E&J Gallo winery, back in the late 1970's.
Jerry

Jerry, thanks and I was hoping you would be able to see/respond to this post. I really like your idea....sure sounds better than simply trying to weld the ears back on. Only other thot is someone might have a good rear manifold section laying around, but that is a very long shot....and to try to successfully remove said part in non-broken condition from a rotting parts truck is probably a pipe dream...

The big rigs usually got used, abused, worn out, and scrapped after a few years of use. The big GMC engines like the 426, 503, and a few others of the same design actually had bolt-on cylinder assemblies that could be removed from the crankcase. After a few re-ring jobs and the cylinders getting taper worn, it was possible to bolt on a new cylinder bank instead of boring and buying new pistons. The big Diesels took the concept a step futher, and used cylinder sleeves that could be swapped instead of changing the whole cylinder assembly. Unfortunately, most of those well-engineered old engines got trashed along with the worn out trucks they powered!
Jerry

Jay,

I will look at my spare engine.

Ed

Ed, thanks!....I would guess that not too many people have a parts 503

Jay, My parts engine is from a COE, so the plumbing is different, so would not work on your Conventional.

Might work to make a whole new end with the bolt pattern intact to weld all the pieces to and make a rigid support for the rest of the system, a lot of work though.

Ed

Ed, thank you....the picture looks just like mine! My GMC parts books shows that, while there were some differences thru the years in regard to the center section, the front and rear manifold sections were the same for all trucks throughout the run of 426 and 503 motors.

Jay,

Is yours a COE or conventional?

Ed

Ed, It is a conventional. If there are differences between the COE and conv manifolds, the parts book doesn't show that.....but then the parts book may have some errors. I don't have enough knowledge to be sure. Thanks

Other than maintaining the original appearance, is a 3-bolt flange the only option? How about fabricating a 4 bolt flange from 1/2" or maybe 5/8" steel plate, and weldng it onto the original manifold after milling the broken flange off? Then make an identical shaped flange for the exhaust pipe. It would also be possible to fabricate some sort of support bracket to keep the weight of the exhaust pipe off the new flange to minimize the strain on it.
Jerry

Jerry, thanks for the followup....I would agree that it is not the only option, and your idea sounds like an 'improved mousetrap'. In looking at the original setup, including what's left of the pipe, I see some room for improvement. It seems that rather than a lip, there was a small 'donut' embossed on the pipe which fit into a corresponding recess in the flange (excuse my terminology, prob a better way to describe it). The asbestos flange gasket makes a good seal, but it looks like there would be room for blowby where the pipe goes into the manifold at the inner edge of the gasket. What would be helpful would be to have an NOS pipe, then the whole picture would become more clear. In any case, I'm about ready to make some welded changes incorporating your ideas. But I'm not against finding a good original manifold piece, and will spend just a little more time looking, before rushing in. You know Murphy's Law about parts: when parts become essential, they're unavailable, and when you don't need them they seem to pop up everywhere....

Cast iron can be incredibly difficult to weld, especially a manifold that's undergone thousands of heat/cool cycles, so be sure whomever does the welding is very capable. Nothing says "you're having a bad day" like an irreplaceable piece of cast iron that just won't take a weld. I got involved in a repair job on a huge centrifugal pump housing that had thrown a piece of the damaged impeller through the side of the pump. The lead man on the job was an oldtimer with 40-something years of experience welding cast iron. We scavenged up all the pieces of the broken casting we could find and pieced them back together like a jigsaw puzzle. It took three days of heating, peening and slow-cooling the casting, making weld beads with nickel-alloy rod of about an inch long at a time. The outlet pipe of that pump was 16" in diameter, and the bowl we were welding on weighed about 400 pounds.
Jerry