Exhaust Manifold Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CCCC · 01-28-2011, 07:32 PM

Talking 1972 402 BB passenger side exhaust manifold.

First, thanks to those who replied earlier with ideas on how to deal with exhaust manifold bolts that have been unmoved for almost 40 years and 100k miles, and might have been "frozen". Good news is that they were not frozen.

Bothersome news is that, as I finally got after the exhaust leak today, found that the front and rear manifold bolts were not snugged up tight - not loose, but easily could get some turn on them. And, these are the two locations of the leaks I could hear with tubing to ear. All other bolts were tight.

Am ready to go back together with the new gasket, but want available experience and knowledge beforehand. Questions:

1. Is it more likely that the bolt at each end of the manifold slowly worked out a bit and enabled the gasket to deform and leak, or that the gasket degraded and blew out a bit, and left the bolts not snug?

2. Is it at all common for a cast manifold for this truck to "bow" out a little bit at its ends. (Have not put the manifold face on a straight edge and do not want to further disconnect and remove unless really important to do it).

3. Other than thoroughly cleaning the bolts, particularly the threads, is there anything additionl that should be done - or anything applied to the threads - before re-assembly? I am an old timer - not up on all of the current chemicals and techniques for these jobs - don't want to miss any improvements.

Thanks for any help.
CCCC

01-28-2011, 07:32 PM	#1
CCCC Registered User Join Date: Mar 2007 Location: San Pedro River, SE Arizona Posts: 734	Exhaust Manifold Help Talking 1972 402 BB passenger side exhaust manifold. First, thanks to those who replied earlier with ideas on how to deal with exhaust manifold bolts that have been unmoved for almost 40 years and 100k miles, and might have been "frozen". Good news is that they were not frozen. Bothersome news is that, as I finally got after the exhaust leak today, found that the front and rear manifold bolts were not snugged up tight - not loose, but easily could get some turn on them. And, these are the two locations of the leaks I could hear with tubing to ear. All other bolts were tight. Am ready to go back together with the new gasket, but want available experience and knowledge beforehand. Questions: 1. Is it more likely that the bolt at each end of the manifold slowly worked out a bit and enabled the gasket to deform and leak, or that the gasket degraded and blew out a bit, and left the bolts not snug? 2. Is it at all common for a cast manifold for this truck to "bow" out a little bit at its ends. (Have not put the manifold face on a straight edge and do not want to further disconnect and remove unless really important to do it). 3. Other than thoroughly cleaning the bolts, particularly the threads, is there anything additionl that should be done - or anything applied to the threads - before re-assembly? I am an old timer - not up on all of the current chemicals and techniques for these jobs - don't want to miss any improvements. Thanks for any help. CCCC __________________ CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp



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