Replacing exhaust manifold (Building a header)

[isaac_alaska]

Went out and put some good miles on the truck today with a bunch of other big off-road trucks. Truck did awesome, but now I can see the exhaust manifold is cracked. Anyone have one for sale? Going to be replacing the whole exhaust system cause it's rusty and falling off. And going to mount the new muffler such that it doesn't hang lower than the frame.
How difficult are the exhaust manifold bolts to get out? I sprayed them with PB blaster, but it's all burned off since then. I'll spray them again.
Thanks!

[nhjohnny1]

manifold are a common issue when the stock hangers rust/wear out and the exhaust hangs on the manifold causing it to crack, I am going to install a braided flex joint in mine and make an attempt to reroute the exhaust as well.

[pwrwagonfire]

You may want to look at replacing the studs when you put on a new manifold, I planned on doing it anyway but was surprised at how bad they were regardless. VPW recommends going with stainless.

I bought a harbor freight stud remover for $8, was definitely worth the price for how easy it made it.
I would recommend draining the radiator/block before taking the manifold off; a few of the studs go into the water jacket, and some of my nuts were fused and pulled these studs out before I noticed what was happening.


-T

[w30bob]

Hi Guys,

The exhaust manifold cracking is a rather common problem. Due to the design of the manifold, they crack most often on the #1 cylinder runner because it's unsupported, as compared to the rest of the runners. As the cast iron heats up and expands cylinder #1 runner is kind of hanging out there in left field and pushes on the two studs in the block. Cast iron is good in compression.......but when the manifold cools off it contracts it pulls on the #1 runner, and since cast iron sucks in tension.........it cracks at the point of least material, which is where the runner curves. The #6 runner is also sort of in the same boat, but has a bit more mass too it to help it withstand the cracking.

That's why it's so important that you use the 4 special brass conical washers and slit nuts to secure the #1 and #6 runners to the block. These allow the manifold runners to move relative to the rest of the manifold and not crack. If you don't know what I'm talking about you can see what they look like here;

http://www.ebay.com/itm/Dodge-M37-Exhau ... 7675.l2557

VPW sells them individually, although they are a bit expensive. I'm sure John has them at Midwest too. They're probably available commercially as well, but I couldn't find them after a quick web search.

You can weld cast iron, but most welders don't understand the material properties of cast iron well enough. And those that do charge a lot to do the job properly, as it's labor intensive and takes a lot of time to do properly. And if you install a repaired manifold without the brass washers/nuts it's just going to crack again.

Getting the studs out of the block shouldn't be too bad.........VPW sells them too, and they offer a kit that included all the studs/nuts/washers to install the manifold. As for the cost of a good used exhaust manifold..........well as usual..........when you need one they're ridiculously expensive. When you don't need one you seem to stumble over them everywhere for cheap. I believe VPW gets $375 + shipping for a good used one. I've seen lot of them at MV meets, almost always under $100.

regards,
bob

[BILL L]

I have NOS ones for $250plus shipping. Autodoc51@aol.com

[isaac_alaska]

Thanks Bill, I may hit you up if I can't find a used take-off.

Do you generally pull the intake and exhaust manifold as one piece and then separate them, or leave the intake attached to the engine?

[BILL L]

Make sure you have the correct acorn nuts and washers on the manifold ends. A lot of times they are missing and replaced with regular nut and flat washers.

[isaac_alaska]

yeah, i'm pretty sure mine have been replaced. the manifold is cracked in the rear, or at least it looks like it is, it's got a bunch of "goop" on it that looks like it was an attempted repair. i'll get a photo next time i'm at the truck

[w30bob]

Isaac,

One thing I forgot to mention.........the intake and exhaust manifold are a "set", so to speak. The gasket flange on both manifolds needs to be exactly in the same plane when the 4 bolts that hold the 2 manifolds together are tightened up.........or else the ears on the shorter manifold will crack off when you go to tighten them down on the engine studs. I assume Dodge bolted them together and then hit the gasket surfaces of both with a surface grinder to get an absolute flat surface. When you mix an intake and an exhaust manifold you need to bolt them together and then check the runner gasket surfaces are perfectly in line with each other, as the 4 bolts around the heat riser don't allow much wiggle room if they're not.

regards,
bob

[isaac_alaska]

If i weld up an intake/exhaust manifold set, out of tubing, is the heat riser necessary? the manifolds by moose page doesn't seem to show any provision for a heat riser. i can understand what the heat riser is supposed to do, but how necessary is it? does being tubing instead of cast make a difference?

[just me]

Heat riser is pretty important. There is good info and a how to for water heat on custom manifolds at Stovebolt.
http://www.langdonsstovebolt.com/store/ ... ort=normal

[isaac_alaska]

That was exactly what I needed. So for a tubing manifold, it's probably easiest to use water heat. Or electric if I can find 24V silicone heating pads... Something tells me they wouldn't provide enough heat though. Probably water is the way to go

[isaac_alaska]

Took a closer look at the manifold, it's not just one crack. There's at least 3 I can see from sure, including one in the intake manifold and a broken bolt that holds the tow manifolds together.

[isaac_alaska]

drew this up today. it's basically a copy of my favorite from the manifolds by moose page

[just me]

Prior experience tells me that exhaust portion would not be very long lived. (unless it was made from some VERY thick wall tubing.) But it looks cool!
I'm currently looking at building a set of 3-2-1 headers for my engine and either a 3X1bbl or 2x2bbl manifold for my engine. The challenge here is to leave clearance to do the valve adjustments while running as none of the commercially available headers have that.