A good ceramic coating inside and out on the Thorley headers such as
provided by Swain Technology http://swaintech.com/sindex.html goes a long
way towards curing the problem. Note that the Swain process is different
than the HPTC process, in that it is a true ceramic process. If you have
seen the two technologies on a header you can see what I mean. The heat is
quickly carried away from the exhaust manifolds and into the exhaust pipes.
>Henry,
>
>I have always maintained and was persuaded to believe that 2 factors play a
>part in out manifold trounle that is other than the usual aging process
>that eats antique car manifolds equally.
>
>First is the fact that the bolt pattern is not uniform to the pressure
>exerted on the manifold. There is a weak area at the center bottom, look
>at the bolt pattern. As the manifold heats up, it will tend to bow out at
>the center blowing out the gaskets and cracking the manifold in extreme cases.
>
>The second is, as you pointed out, the manifolds heat up more than a car
>because of the torque the motor has to create to drag the coach carcus.
>How long can mere cast steel take such abuse, maybe if they were made of
>Cryptonite they would last longer!
>
>Actually, I did find another problem with manifolds that have been surfaced
>several times. So much of the mate surface gets sanded away to flatten the
>area that there is no longer enough room for the loi dip stick tude to go
>between the left manifold & head. It hols the manifold away from the head
>and causes gaskets to burn out. I have one in the shop now that has this
>ailment right now that we just rebuilt!
>
>Headers are the only viable fix but they do not come without trouble of
>their own. You must constantly tighten the bolts on headers, ask Nate
>about that! They do a combination of compressing the fiber gasket that
>must be used on headers and back out the bolts from the heating & cooling
>processes that they must endure.
>
>You have an interesting question and one I would like to see the data on to
>support & refute my understanding on this matter.
>
>Survey on, young Skywalker!
>
>Jim Bounds
>-------------------
>>>Dear Netters,
>>>
>>>Does anyone know what is different about our GMCs that causes us so much
>>>grief with the exhaust manifolds (i.e., warping and cracking)?
>>
>>I don't know that we're all that different from other gasoline big block
>>engines used in heavier RVs or small blocks used in some lighter RVs.
>>
>>I DON'T KNOW IF IT'S TRUE, but here's what I was told by mechanics who
>>regularly service the coaches when we first started looking at motorhomes:
>>any engine run at wide open throttle for long periods of time at low speeds
>>(ie climbing long grades) will significantly stress the exhaust manifold.
>>Evidently the right side manifold on the 350s used in a number of Class C
>>MHs is a chronic problem around here. And they saw similar problems with
>>the 454 in bigger MHs.
>>
>>The comments were pretty universal from mechanics in the area - they see a
>>lot of cracked exhaust manifolds in comparison to the same engine in a
>>passenger car or lightly used truck.
>>
>>Note: this is not a scientific sampling. The mechanics might be mistaken,
>>they may be over-reacting, or they could be nuts. But then, they might just
>>be right.
>>
>>>Does an overly
>>>lean running engine heat the manifolds?
>>
>>I don't know about lesn heating the manifolds, but I can tell you that
>>leaking exhaust manifolds can cause a local leaning of the exhaust that
>>raises temps on the exhause valves.
>>
>> Do these babies glow in the dark
>>>during a hard pull?
>>
>>I haven't looked to see if they literally glow, but I can tell you that
>>they get pretty hot.
>>
>> What about the mufflers mounted ahead of the Y. Is this
>>>extra weight hanging from the manifolds significant enough to cause warpage
>>>if indeed the manifolds were glowing red hot and bouncing down a rough
>>>stretch of road? Do I sound crazy?
>>
>>No crazier than the rest of us. After all, you DO own a 27 year old MH.
>>
>>Good luck in your information quest!
>>
>>Henry
>>
>>Henry Davis Consulting, Inc / new product consulting
>>PO Box 1270 / product readiness reviews
>>Soquel, Ca 95073 / IP reviews
>>ph: (831) 462-5199 / full service marketing
>>fax: (831) 462-5198
>>http://www.henry-davis.com/ http://www.henry-davis.com
>>
>>
>>
>
>
provided by Swain Technology http://swaintech.com/sindex.html goes a long
way towards curing the problem. Note that the Swain process is different
than the HPTC process, in that it is a true ceramic process. If you have
seen the two technologies on a header you can see what I mean. The heat is
quickly carried away from the exhaust manifolds and into the exhaust pipes.
>Henry,
>
>I have always maintained and was persuaded to believe that 2 factors play a
>part in out manifold trounle that is other than the usual aging process
>that eats antique car manifolds equally.
>
>First is the fact that the bolt pattern is not uniform to the pressure
>exerted on the manifold. There is a weak area at the center bottom, look
>at the bolt pattern. As the manifold heats up, it will tend to bow out at
>the center blowing out the gaskets and cracking the manifold in extreme cases.
>
>The second is, as you pointed out, the manifolds heat up more than a car
>because of the torque the motor has to create to drag the coach carcus.
>How long can mere cast steel take such abuse, maybe if they were made of
>Cryptonite they would last longer!
>
>Actually, I did find another problem with manifolds that have been surfaced
>several times. So much of the mate surface gets sanded away to flatten the
>area that there is no longer enough room for the loi dip stick tude to go
>between the left manifold & head. It hols the manifold away from the head
>and causes gaskets to burn out. I have one in the shop now that has this
>ailment right now that we just rebuilt!
>
>Headers are the only viable fix but they do not come without trouble of
>their own. You must constantly tighten the bolts on headers, ask Nate
>about that! They do a combination of compressing the fiber gasket that
>must be used on headers and back out the bolts from the heating & cooling
>processes that they must endure.
>
>You have an interesting question and one I would like to see the data on to
>support & refute my understanding on this matter.
>
>Survey on, young Skywalker!
>
>Jim Bounds
>-------------------
>>>Dear Netters,
>>>
>>>Does anyone know what is different about our GMCs that causes us so much
>>>grief with the exhaust manifolds (i.e., warping and cracking)?
>>
>>I don't know that we're all that different from other gasoline big block
>>engines used in heavier RVs or small blocks used in some lighter RVs.
>>
>>I DON'T KNOW IF IT'S TRUE, but here's what I was told by mechanics who
>>regularly service the coaches when we first started looking at motorhomes:
>>any engine run at wide open throttle for long periods of time at low speeds
>>(ie climbing long grades) will significantly stress the exhaust manifold.
>>Evidently the right side manifold on the 350s used in a number of Class C
>>MHs is a chronic problem around here. And they saw similar problems with
>>the 454 in bigger MHs.
>>
>>The comments were pretty universal from mechanics in the area - they see a
>>lot of cracked exhaust manifolds in comparison to the same engine in a
>>passenger car or lightly used truck.
>>
>>Note: this is not a scientific sampling. The mechanics might be mistaken,
>>they may be over-reacting, or they could be nuts. But then, they might just
>>be right.
>>
>>>Does an overly
>>>lean running engine heat the manifolds?
>>
>>I don't know about lesn heating the manifolds, but I can tell you that
>>leaking exhaust manifolds can cause a local leaning of the exhaust that
>>raises temps on the exhause valves.
>>
>> Do these babies glow in the dark
>>>during a hard pull?
>>
>>I haven't looked to see if they literally glow, but I can tell you that
>>they get pretty hot.
>>
>> What about the mufflers mounted ahead of the Y. Is this
>>>extra weight hanging from the manifolds significant enough to cause warpage
>>>if indeed the manifolds were glowing red hot and bouncing down a rough
>>>stretch of road? Do I sound crazy?
>>
>>No crazier than the rest of us. After all, you DO own a 27 year old MH.
>>
>>Good luck in your information quest!
>>
>>Henry
>>
>>Henry Davis Consulting, Inc / new product consulting
>>PO Box 1270 / product readiness reviews
>>Soquel, Ca 95073 / IP reviews
>>ph: (831) 462-5199 / full service marketing
>>fax: (831) 462-5198
>>http://www.henry-davis.com/ http://www.henry-davis.com
>>
>>
>>
>
>
