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| Re: Cracked RH Exhaust Manifold [message #166773 is a reply to message #166750 ] |
Wed, 18 April 2012 21:56   |
 Bob de Kruyff
Messages: 2344
Registered: January 2004
Location: Chandler, AZ |
Senior Member |
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| MangoMushroom wrote on Wed, 18 April 2012 17:24 |
Installed a new Remflex gasket to replace the one I'd installed 50k miles ago, and fixed the exhaust leak. For about 2 days.
Then, RH exhaust manifold cracked. Great. It is visibly cracked on the outside, which is making the flat faces warp and allow exhaust leak
What is the best gameplan? Rehab the existing one? Find a new one? Any suggestions where I might find one? Yes, I know, GMC Swap Meet 
Thanks everybody!
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Although they can be welded, it takes a real pro and even then, it's a marginal fix. You can find these on ebay or soliscit someone who has put on headers. Although many folks have switched to headers, that may not be your best choice right now.Cinnabar also has new ones.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Cracked RH Exhaust Manifold [message #166794 is a reply to message #166773 ] |
Thu, 19 April 2012 04:00 |
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MangoMushroom
Messages: 39
Registered: August 2008
Location: San Francisco |
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Bob, why would headers not be my best option? Price I suppose?
The truth is, a used ex manifold would be cheap and I can install myself. I'm pretty sure headers would cost at least 5x as much and I'm about 5x less likely to be able to do the job myself 
Another thing to consider is that I've got an old dirty engine that has likely never been rebuilt, and isn't a work of art to look at. That being said, she has been a trooper for the 5 years I've had her, and generally with my coach I've tried to stay faithful to original design when replacing things. Might not be the smartest thing to do, but I have somewhat of a romantic notion of leaving things the way they were originally designed.
[Updated on: Thu, 19 April 2012 04:05]
****MangoMushroom
`76 GMC Birchaven
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| Re: [GMCnet] Cracked RH Exhaust Manifold [message #166822 is a reply to message #166794 ] |
Thu, 19 April 2012 12:22 |
Robert Mueller
Messages: 9039
Registered: July 2007
Location: Sydney, Australia |
Senior Member |
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Andre,
Check eBay, I just bought a left manifold for less than $100.
Regards,
Rob M.
-----Original Message-----
From: Andre Mandel
Bob, why would headers not be my best option? Price I suppose?
The truth is, a used ex manifold would be cheap and I can install myself.
I'm pretty sure headers would cost at least 5x as much and I'm about 5x less
likely to be able to do the job myself :?
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Rob Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Cracked RH Exhaust Manifold [message #166823 is a reply to message #166822 ] |
Thu, 19 April 2012 12:42 |
hertfordnc
Messages: 813
Registered: September 2009
Location: East NC |
Senior Member |
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Andre,
I have a pair of GMC manifolds. Free for the price of shipping (round UP on the shipping, i always lose money)
I got them in a trade, not knowing they were usesless on the REVCON. (no comments Rob and Dan)
THey've been resurfaced once. not sure if they took too much off.
I can send photos.
dave - zip code 27944
Dave & Ellen Silva
1972 Revcon Olds 455, toro drive train. All Stock
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| Re: [GMCnet] Cracked RH Exhaust Manifold [message #166830 is a reply to message #166823 ] |
Thu, 19 April 2012 13:34 |
Robert Mueller
Messages: 9039
Registered: July 2007
Location: Sydney, Australia |
Senior Member |
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Dave,
Jeez I was going to say something nice but I guess I won't! ;-)
Regards,
Rob M.
-----Original Message-----
From: dave silva
Andre,
I have a pair of GMC manifolds. Free for the price of shipping (round UP on
the shipping, i always lose money)
I got them in a trade, not knowing they were usesless on the REVCON. (no
comments Rob and Dan)
THey've been resurfaced once. not sure if they took too much off.
I can send photos.
dave - zip code 27944
--
Dave & Ellen Silva
1972 Revcon Olds 455, toro drive train. All Stock
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Rob Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: Cracked RH Exhaust Manifold [message #166831 is a reply to message #166791 ] |
Thu, 19 April 2012 13:50 |
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Mike Miller
Messages: 3309
Registered: February 2004
Location: Hillsboro, Oregon |
Senior Member |
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The above is an over simplification. For the most part, headers will not provide any improvement in performance with our engines in our application. (Too low RPM's for the flow improvements of headers to really "show".) In fact you might loose a little torque.
There is something to be said for keeping something stock. The manifolds make a simpler system and where designed to have NO gasket between the engine and manifold. But age (rust and heat) and leaks (from the rust and warping from the heat) have combined to make a seal without gaskets almost impossible.
So... you'll need a gasket. The gasket will interfere with the cooling of the manifold. (Normally the engine block would provide this cooling.) As a result the manifolds will crack easier than they would originally.
The advantage of headers, for us, is that they do not crack so you are more likely to keep a good seal. They flex with the heat and cool themselves better than a manifold with a gasket. (Leaving more heat around the motor... oh-well nothing is all good.)
SO... what would I do in your situation? How long do you plan on keeping the coach? If not long, find a replacement manifold. (I understand that the right one is easier to find (cheaper) than the left. Also they are different 455/403.) If you plan on keeping the coach, go with headers.
Mike Miller -- Hillsboro, OR -- on the Black list
(#1)'73 26' exPainted D. -- (#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
http://m000035.blogspot.com
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| Re: [GMCnet] Cracked RH Exhaust Manifold [message #166834 is a reply to message #166831 ] |
Thu, 19 April 2012 13:59 |
Robert Mueller
Messages: 9039
Registered: July 2007
Location: Sydney, Australia |
Senior Member |
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Mike,
Here's a link to dyno runs that JimB had done on an engine:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=40002
If the heads and manifold are in good shape one can use these gaskets and
not loose heat transfer.
http://www.bdub.net/lenzi/index.html#CopperGaskets
Regards,
Rob M.
-----Original Message-----
From: Mike Miller
The above is an over simplification. For the most part, headers will not
provide any improvement in performance with our engines in our application.
(Too low RPM's for the flow improvements of headers to really "show".) In
fact you might loose a little torque.
There is something to be said for keeping something stock. The manifolds
make a simpler system and where designed to have NO gasket between the
engine and manifold. But age (rust and heat) and leaks (from the rust and
warping from the heat) have combined to make a seal without gaskets almost
impossible.
So... you'll need a gasket. The gasket will interfere with the cooling of
the manifold. (Normally the engine block would provide this cooling.) As
a result the manifolds will crack easier than they would originally.
The advantage of headers, for us, is that they do not crack so you are more
likely to keep a good seal. They flex with the heat and cool themselves
better than a manifold with a gasket. (Leaving more heat around the
motor... oh-well nothing is all good.)
SO... what would I do in your situation? How long do you plan on keeping
the coach? If not long, find a replacement manifold. (I understand that
the right one is easier to find (cheaper) than the left. Also they are
different 455/403.) If you plan on keeping the coach, go with headers.
--
Mike
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Rob Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: Cracked RH Exhaust Manifold [message #166844 is a reply to message #166840 ] |
Thu, 19 April 2012 16:04 |
Bob Raef
Messages: 147
Registered: July 2009
Location: Ruidoso, NM |
Senior Member |
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Andre
The exhaust manifolds off of the 403 will not fit on your 455 engine.
Bob Raef, KF5TYA
Ruidoso, NM
1976 XBirchaven Rear Bath (in rehab)
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| Re: Cracked RH Exhaust Manifold [message #166846 is a reply to message #166845 ] |
Thu, 19 April 2012 16:16 |
Bob Raef
Messages: 147
Registered: July 2009
Location: Ruidoso, NM |
Senior Member |
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If his is a 1976 Birchaven then it will have a 455 motor if it has not been swapped out for something other than a 455. the manifolds on ebay are for a 403 and will not fit a 455.
Bob Raef, KF5TYA
Ruidoso, NM
1976 XBirchaven Rear Bath (in rehab)
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