Cracking exhaust manifolds and leaks

mattyj858 · June 21, 2016, 11:46 PM

Hi guys hoping someone might be able to help. I took my 73 440 into a very reputable exhaust shop, and it turned out I had cracks in both exhaust manifolds. I replaced both manifolds that were milled and inspected from another respected machine shop. I also at the time did a complete exhaust system, 3 1/2" to 3" so I know there's no obstruction or crazy back pressure. 80 miles later it started to leak so took it back thinking it just needed to retourqued. Turns out I cracked another manifold. The shop had a hell of a time getting the replacement to seal properly, and took them 5 times of installing ( was milled) to get it to seal. They also used aluminum gaskets. They said something about a bump that is normal and hard to get a proper seal? Picked it today, drove 2 miles and the motor started a clapping sound on the passenger side, same side as before. There is definitely an exhaust leak and I have the feeling I have another cracked passenger exhaust manifold. Although the temp gauge looked good, the block seemed really hot at 400 degrees with a temp gun. Th guys at the shop are at a loss. They mentioned my old carb could have a stuck float causing the motor to run lean and heating the block. My Thermoquad is shot ( loose shaft and running on primaries only) and already bought an Edelbrock 1411 but wanted to get th exhaust issue fixed first.
Could the bad carb be related to the heat issue and causing the manafolds to leak and crack?
The guys also told me they had to mill the corner of passenger manifold so it would clear the valve cover, seemed odd to me. These were American made manifolds and they have a set of China made but were reluctant to use them. Any insight is greatly appreciated

legomybago · June 22, 2016, 09:50 AM

I would buy "new" exhaust manifolds. The 440 manifolds are known for cracking, they are getting old! Sounds like to me they installed pre-cracked manifolds.
http://www.ebay.com/itm/7-2-440-Dodge-Chrysler-Truck-Motorhome-New-Exhaust-Manifold-/272259841861?hash=item3f63f37f45:g:40cAAOSwOtBXTbNB&vxp=mtr

mattyj858 · June 22, 2016, 10:48 AM

I know they were purchased from a machine shop that specializes in manifolds and were inspected before installed.
Based on manifold costs I am more inclined to put on a reliable set of headers.

legomybago · June 22, 2016, 02:41 PM

Maybe the "reputable" shop should make good on installing cracked/warped manifolds on your rig.....you drove 2 miles and the manifold started leaking again?? The shop needs to make this right in my opinion. If you do buy headers, I wouldn't have that shop install them. Good luck

Rickf1985 · June 22, 2016, 07:44 PM

I have to agree, the manifolds usually crack as they are cooling off not when they are heating up, unless they were tightened to tight and they could not move on the gaskets. Cast iron has to be able to expand and contract. Headers would be a good choice as long as you buy GOOD headers. You get what you pay for. IF you can find them in 14 gauge tubing then they are very good headers and will last the life of the vehicle. They are probably going to guaranteed for that long as well. They will NOT be cheap!

mattyj858 · June 23, 2016, 01:55 AM

Quote from: legomybago on June 22, 2016, 02:41 PM
Maybe the "reputable" shop should make good on installing cracked/warped manifolds on your rig.....you drove 2 miles and the manifold started leaking again?? The shop needs to make this right in my opinion. If you do buy headers, I wouldn't have that shop install them. Good luck

Yes both shops are standing behind this 100%, they are good guys.

I am just trying to get some insight here, not pointing fingers at the shops. Trying to figure out if anyone has faced a similar issue

mattyj858 · June 23, 2016, 01:59 AM

Quote from: Rickf1985 on June 22, 2016, 07:44 PM
I have to agree, the manifolds usually crack as they are cooling off not when they are heating up, unless they were tightened to tight and they could not move on the gaskets. Cast iron has to be able to expand and contract. Headers would be a good choice as long as you buy GOOD headers. You get what you pay for. IF you can find them in 14 gauge tubing then they are very good headers and will last the life of the vehicle. They are probably going to guaranteed for that long as well. They will NOT be cheap!

Yes agree. I already spent $1250 on the manifolds and whole exhaust system so I honestly can afford $800+ on good headers. I spoke with the shop about the possibility of switching to an affordable header set and the shop said they refuse to install cheap headers.

legomybago · June 23, 2016, 09:41 AM

Damn son! 1,250 is some bucks for an exhaust system. For that money you "should" be concerned, and deserve to have it 100% correct.

mattyj858 · June 23, 2016, 10:16 AM

Yep two exhaust manafolds, all new 3 1/2" to 3" tubing and muffler. The tube work is awesome it's just the darn manafolds...

Surfinhurf · June 23, 2016, 01:07 PM

Is the exhaust tubing hung right? A motorhome exhaust system is HEAVY. That weight and torque could crack manifolds. If you do go to headers you most likely will have to redo the tube work, the exit point of the headers will be different than the stock manifolds.

Good Luck
HURF

mattyj858 · June 23, 2016, 03:26 PM

Good point on the weight I know this guy does a lot of RVs so I'm assuming. He has taken that into consideration but I will bring that up.
Does anyone have any input in regards to a bad carburetor over leaning the mixture and heating up the manifolds? Trying to figure out if it makes sense to install my new Edelbrock before fixing the exhaust.
As I mentioned my temp gauge seemed fine but my heads and manifolds were really hot. I have the feeling the heat has something to do with the leaks and crack

Rickf1985 · June 23, 2016, 06:05 PM

Leaning out the mixture might heat up the engine some but not the manifolds, over rich would heat them up due to unburned gas in the exhaust. If the manifolds were cracked and welded then they are probably going to keep cracking. There is not as much airflow over them as in a car so they do get hotter in an RV. I have had better luck on Ford big block manifolds which are also famous for cracking by brazing them since the brass will give a little. And this was on 4x4 pick ups running through water holes so red hot exhaust meets ice cold water! That was where I found that the tightening torque was critical so the manifold can slide on the gasket as it expands and contracts. Ask anybody that has a Dodge diesel pick up how their exhaust pops as it cools down. The holes are slotted so the manifold can move.