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Plagued With Exhaust gasket leaks [message #270952]

Sun, 01 February 2015 12:31

Neil

Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...

Karma: 1

Senior Member

Is there any particular reason why the driver's side of the motor is more prone to developing an exhaust leak in the center of the manifold?

I do have Thorley headers. With a new gasket everything is fine for anywhere from 300 to 2,000 miles, then I get a leak. This time it is dead center of the flange.

The passenger side does not seem to have this problem. Could it be a warped flange? But then why would it snug up and work for a while?

Thanks for your thoughts.

Neil
76 Eleganza now sold
Los Angeles

[Updated on: Sun, 01 February 2015 12:31]

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Re: Plagued With Exhaust gasket leaks [message #270953 is a reply to message #270952]

Sun, 01 February 2015 12:47

jtblank

Messages: 237
Registered: June 2007
Location: Tulare, CA

Karma: 1

Senior Member

Use rim flex gaskets, you'll never have problems again. Your flange may not be true so when you have it off you could have it surfaced. I had same thing, leaks develop over time but since using rim flex never again, it's been at least 6 years since I changed. You can get them from one of the Jim's or from Rim Flex direct but price is about the same, so I buy from GMC vendors.
You can read about them at http://catalog.remflex.com/
Hope this helps!

John Blankenship '76 Palm Beach Tulare, CA

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Re: [GMCnet] Plagued With Exhaust gasket leaks [message #270954 is a reply to message #270952]

Sun, 01 February 2015 12:50

James Hupy

Messages: 6806
Registered: May 2010

Karma: -62

Senior Member

Are you using Remflex gaskets? If not, try them. They will compensate for
uneven flanges. Don't drive with a blown gasket very far. It will erode the
head sealing surface and will require machine work to correct.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Feb 1, 2015 10:31 AM, "Neil Martin" wrote:

> Is there any particular reason whey the driver's side of the motor is more
> prone to developing an exhaust leak in the center of the manifold?
>
> I do have Thorley headers. Wit a new gasket everything is fine for
> anywhere from 300 to 2,000 miles, then I get a leak. This time it is dead
> center
> of the flange.
>
> The passenger side does not seem to have this problem. Could it be a
> warped flange? But then why would it snug up and work for a while?
>
> Thanks for your thoughts.
> --
> Neil
> 76 Eleganza
> Los Angeles
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>
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Re: [GMCnet] Plagued With Exhaust gasket leaks [message #270964 is a reply to message #270954]

Sun, 01 February 2015 14:55

Otterwan

Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...

Karma: 0

Senior Member

I don't think this will work with the olds headers because the Olds engines use so few bolts, but on BBC we use to cut the header flange between the first and second and between the third and forth pipes. This allowed the header to flex and the flanges to seat better. However the BBC has 8 exhaust bolts, while the Olds hs only 4.

http://www.jegs.com/images/photos/500/555/555-210755.jpg

http://i.ebayimg.com/00/s/MTIwMFgxNjAw/$(KGrHqV,!nME9g(F02SzBPf1ghKGEQ~~60_35.JPG

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Re: [GMCnet] Plagued With Exhaust gasket leaks [message #270982 is a reply to message #270952]

Sun, 01 February 2015 18:34

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Neil,

Seems to me it would be cost and time effective if you removed that header and took it to a machine shop and had them check the
flange to see if it is flat.

You could try Dave Lenzi's copper gaskets: http://www.bdub.net/lenzi/index.html#CopperGaskets

Probably would be a good idea to call him first as I don't know if they will work with headers.

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426

-----Original Message-----
From: Neil Martin

Is there any particular reason whey the driver's side of the motor is more prone to developing an exhaust leak in the center of the
manifold?

I do have Thorley headers. Wit a new gasket everything is fine for anywhere from 300 to 2,000 miles, then I get a leak. This time
it is dead center of the flange.

The passenger side does not seem to have this problem. Could it be a warped flange? But then why would it snug up and work for a
while?

Thanks for your thoughts.
--
Neil

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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

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Re: Plagued With Exhaust gasket leaks [message #270985 is a reply to message #270952]

Sun, 01 February 2015 18:47

jhbridges

Messages: 8412
Registered: May 2011
Location: Braselton ga

Karma: -74

Senior Member

My hotrod toad (88 Ranger, strung out 302 CID engine) suddenly developed an appetite for exhaust gaskets. The side with the cut apart flanges lasted marginally longer than the solid side, but not much. Some poking about showed that an exhaust change I made required shortening the exhaust pipe between the headers and the mufflers by a couple of inches, changing the 'twist' factor under acceleration. Additionally, the left motor mount loosened, allowing the engine to move about a bit more. The combination let the header flanges move - or at least try to - due to the lever action of the headers and pipes and the way they're mounted on hangers at the rear of the pipes and in front of the mufflers.
Bottom line - make sure your engine mounts are tight and the engine isn't moving about more than it should. It won't take much, the exhaust system on these coaches is fairly rigid towards the rear.

--johnny

Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons. Braselton, Ga. I forgive them all, save those who hurt the dogs. They must answer to me in hell

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Re: Plagued With Exhaust gasket leaks [message #270986 is a reply to message #270952]

Sun, 01 February 2015 18:51

Chris Tyler

Messages: 458
Registered: September 2013
Location: Odessa FL

Karma: 7

Senior Member

I have been a big believer in copper gaskets with permatex spray copper sealer amd locking bolts.
These Remflex gaskets are worth a look.I have a small leak myself on the driver side with Thorley headers

Sanderson headers have a bead, they recomend permatex high temp silicone only. Im about to put a set on my lincoln 460.

Curious...has anyone used the Sanderson SS shorties on the GMC?

76 Glenbrook

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Re: [GMCnet] Plagued With Exhaust gasket leaks [message #270994 is a reply to message #270986]

Sun, 01 February 2015 21:55

Mr ERFisher

Messages: 7117
Registered: August 2005

Karma: 2

Senior Member

Read here
http://gmcmotorhome.info/engine.html#headers

Copper for headers
Erf

On Sunday, February 1, 2015, Chris Tyler wrote:

> I have been a big believer in copper gaskets with permatex spray copper
> sealer amd locking bolts.
> These Remflex gaskets are worth a look.I have a small leak myself on the
> driver side with Thorley headers
>
> Sanderson headers have a bead, they recomend permatex high temp silicone
> only. Im about to put a set on my lincoln 460.
>
> Curious...has anyone used the Sanderson SS shorties on the GMC?
>
> --
> 76 Glenbrook
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>

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Re: [GMCnet] Plagued With Exhaust gasket leaks [message #270997 is a reply to message #270994]

Sun, 01 February 2015 22:08

hal kading

Messages: 642
Registered: February 2004
Location: Las Cruces NM

Karma: 4

Senior Member

Remember if you go to Remflex gaskets they have two versions, one for headers and one for stock exhaust manifolds.

Hal Kading 78 Buskirk Stretch Las Cruces NM

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Re: [GMCnet] Plagued With Exhaust gasket leaks [message #271000 is a reply to message #270997]

Sun, 01 February 2015 22:38

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

You stated that you tighten up the bolts and it seals again. Have you considered installing bolt locks. Jim K. use to have them. Give him a call.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: Plagued With Exhaust gasket leaks [message #271082 is a reply to message #270952]

Mon, 02 February 2015 20:09

Bob de Kruyff

Messages: 4260
Registered: January 2004
Location: Chandler, AZ

Karma: 1

Senior Member

Neil wrote on Sun, 01 February 2015 11:31

Is there any particular reason why the driver's side of the motor is more prone to developing an exhaust leak in the center of the manifold?

I do have Thorley headers. With a new gasket everything is fine for anywhere from 300 to 2,000 miles, then I get a leak. This time it is dead center of the flange.

The passenger side does not seem to have this problem. Could it be a warped flange? But then why would it snug up and work for a while?

Thanks for your thoughts.

Are you still running two mufflers? If so, are they matched and not rusted and plugged so that both have equal back pressure?

Bob de Kruyff
78 Eleganza
Chandler, AZ

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Re: Plagued With Exhaust gasket leaks [message #271096 is a reply to message #271082]

Tue, 03 February 2015 09:13

Neil

Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...

Karma: 1

Senior Member

Bob - only one muffler.

I ordered copper gaskets and will give that a try.

Neil
76 Eleganza now sold
Los Angeles

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