Cracked exhaust manifold 396 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

northerngmc · 07-25-2016, 10:22 PM

Over the last couple of months I have noticed an exhaust leak on my 68 C20 with a 396, turbo 400. I thought it was probably a loose manifold or a collector gasket that was loose as the noise would go away once the engine warmed up.

Today I noticed that the left manifold has a crack in it!

Can an exhaust manifold be welded? I know it is is cast and this adds difficulty, but how much difficulty?

If I go shopping for another manifold how exclusive are bbc manifolds to trucks?

Any other reasonably suggestions?

The truck is fairly original and a bit of a survivor truck so I am not looking to go to headers or swap the entire exhaust system.
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northerngmc · 07-25-2016, 10:31 PM

Is it really this simple?

http://m.ebay.ca/itm/Exhaust-Manifol...256?nav=SEARCH
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**70STOVEBOLT** · 07-25-2016, 11:10 PM

Yeah probably, I have seen s lot of repops. I think the big cars used the same ones.

**71CHEVYSHORTBED402** · 07-25-2016, 11:30 PM

Quote:

Originally Posted by northerngmc

Is it really this simple?

http://m.ebay.ca/itm/Exhaust-Manifol...256?nav=SEARCH
Posted via Mobile Device

Wow........That looks pretty close to original. Edit, I have a spare LH side with a hairline crack. It takes up space and has no value. You need a "new" manifold.

northerngmc · 07-26-2016, 05:24 PM

Where on the manifold should I look to find the casting number.
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**Already Gone** · 07-26-2016, 05:57 PM

Blaine I have a new repro exhaust manifold that came with a 70 BB truck I bought a few years ago. I'm not sure what side but can check tonight when I get home.

68Gold/white · 07-26-2016, 06:41 PM

They can be welded, also.
There's a special "cast" welding rod. You cannot use a grinding disc to clean out the crack, you have to use a carbide bit. They also make a "gouging rod" that is used ahead of the welding, some how it prepares the surface for the cast rod.
I'm no expert at all this, my good friend has a machine shop, showed me several years ago. It does work.
Nickle rod is NOT the same thing...

northerngmc · 07-26-2016, 08:26 PM

http://www.yenko.net/ubbthreads/pics...8-img_0286.jpg

How different are bbc exhaust manifolds. Part number on the side 3914613. This does not align with the ATP cross reference in the eBay ad I posted above.
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hugger6933 · 07-26-2016, 08:49 PM

It is not uncommon cracked manifolds were common even in to the squares and the 88-98 style as well.

**Already Gone** · 07-26-2016, 11:50 PM

As luck would have it I have a right side exhaust manifold.

Luvinit · 07-27-2016, 12:02 AM

I,m needing a left one for my 72 402, I see LMC lists them also.

northerngmc · 07-27-2016, 01:22 AM

Quote:

Originally Posted by Already Gone

As luck would have it I have a right side exhaust manifold.

Thanks for checking.

Looks like my right one has already been replaced.
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**71CHEVYSHORTBED402** · 07-28-2016, 12:56 AM

The casting numbers can vary: Here's some info. most of which I lifted off SSTIM:

The following part numbers are service replacement parts.

But don't expect a number in the parts manual to match a part you pulled from your truck.

Overall its real simple, the replacement manifolds at the time of printing (5/79) were:
3994045 LH
333846 RH (3916178 to 3994046 to 333846)
with A.I.R. this is the air pump for emission reduction (Not A/C).
343787 LH
353030 RH

There is nothing on the parts manual page showing application specific parts for a 396-402 C10-30 Air Conditioned vehicle. If there were it would probably be notated w/AC, C.A.C., or C60.

07-25-2016, 10:22 PM	#1
northerngmc Registered User Join Date: Jan 2004 Location: Whitehorse YK Canada Posts: 2,651	Cracked exhaust manifold 396 Over the last couple of months I have noticed an exhaust leak on my 68 C20 with a 396, turbo 400. I thought it was probably a loose manifold or a collector gasket that was loose as the noise would go away once the engine warmed up. Today I noticed that the left manifold has a crack in it! Can an exhaust manifold be welded? I know it is is cast and this adds difficulty, but how much difficulty? If I go shopping for another manifold how exclusive are bbc manifolds to trucks? Any other reasonably suggestions? The truck is fairly original and a bit of a survivor truck so I am not looking to go to headers or swap the entire exhaust system. Posted via Mobile Device

07-25-2016, 10:31 PM	#2
northerngmc Registered User Join Date: Jan 2004 Location: Whitehorse YK Canada Posts: 2,651	Re: Cracked exhaust manifold 396 Is it really this simple? http://m.ebay.ca/itm/Exhaust-Manifol...256?nav=SEARCH Posted via Mobile Device

07-25-2016, 11:10 PM	#3
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,239	Re: Cracked exhaust manifold 396 Yeah probably, I have seen s lot of repops. I think the big cars used the same ones. __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Power windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear

07-26-2016, 05:24 PM	#5
northerngmc Registered User Join Date: Jan 2004 Location: Whitehorse YK Canada Posts: 2,651	Re: Cracked exhaust manifold 396 Where on the manifold should I look to find the casting number. Posted via Mobile Device

07-26-2016, 05:57 PM	#6
Already Gone 70+ ( Old Skool Club ) Join Date: Nov 2003 Location: Saskatoon, Saskatchewan ,Canada Posts: 9,080	Re: Cracked exhaust manifold 396 Blaine I have a new repro exhaust manifold that came with a 70 BB truck I bought a few years ago. I'm not sure what side but can check tonight when I get home. __________________ 1972 C10 Custom/Deluxe 613 Highlander 406/700R4 1999 White Tahoe LS 4x2 with Z56 Police Package 1992 K1500 GMC Suburban Members I have personally met: MusicMan70 - HeavyD - ChewyChevy67 - StingRay -71SWB4x4 - 67 Burb - DeadheadNM - too much stuff - bc65 - das601 " Circumsatances Do Not Change Responsibility " " The Sky is not the Limit, Your Mind is." Marilyn Monroe .. RIP Charlie Watts 1941 - 2021

07-26-2016, 06:41 PM	#7
68Gold/white Registered User Join Date: Sep 2011 Location: Ark City, Kansas Posts: 3,306	Re: Cracked exhaust manifold 396 They can be welded, also. There's a special "cast" welding rod. You cannot use a grinding disc to clean out the crack, you have to use a carbide bit. They also make a "gouging rod" that is used ahead of the welding, some how it prepares the surface for the cast rod. I'm no expert at all this, my good friend has a machine shop, showed me several years ago. It does work. Nickle rod is NOT the same thing...

07-26-2016, 08:26 PM	#8
northerngmc Registered User Join Date: Jan 2004 Location: Whitehorse YK Canada Posts: 2,651	Re: Cracked exhaust manifold 396 http://www.yenko.net/ubbthreads/pics...8-img_0286.jpg How different are bbc exhaust manifolds. Part number on the side 3914613. This does not align with the ATP cross reference in the eBay ad I posted above. Posted via Mobile Device

07-26-2016, 08:49 PM	#9
hugger6933 Registered User Join Date: Oct 2008 Location: Marianna Arkansas Posts: 7,259	Re: Cracked exhaust manifold 396 It is not uncommon cracked manifolds were common even in to the squares and the 88-98 style as well.

07-26-2016, 11:50 PM	#10
Already Gone 70+ ( Old Skool Club ) Join Date: Nov 2003 Location: Saskatoon, Saskatchewan ,Canada Posts: 9,080	Re: Cracked exhaust manifold 396 As luck would have it I have a right side exhaust manifold. Attached Images __________________ 1972 C10 Custom/Deluxe 613 Highlander 406/700R4 1999 White Tahoe LS 4x2 with Z56 Police Package 1992 K1500 GMC Suburban Members I have personally met: MusicMan70 - HeavyD - ChewyChevy67 - StingRay -71SWB4x4 - 67 Burb - DeadheadNM - too much stuff - bc65 - das601 " Circumsatances Do Not Change Responsibility " " The Sky is not the Limit, Your Mind is." Marilyn Monroe .. RIP Charlie Watts 1941 - 2021

07-27-2016, 12:02 AM	#11
Luvinit Registered User Join Date: Jul 2014 Location: Humboldt,Sask. Posts: 42	Re: Cracked exhaust manifold 396 I,m needing a left one for my 72 402, I see LMC lists them also. __________________ 1972 Cheyenne Longhorn k20, 402, A/C

07-28-2016, 12:56 AM	#13
71CHEVYSHORTBED402 Senior Member Join Date: Feb 2009 Location: Northern Nevada Posts: 7,160	Re: Cracked exhaust manifold 396 The casting numbers can vary: Here's some info. most of which I lifted off SSTIM: The following part numbers are service replacement parts. But don't expect a number in the parts manual to match a part you pulled from your truck. Overall its real simple, the replacement manifolds at the time of printing (5/79) were: 3994045 LH 333846 RH (3916178 to 3994046 to 333846) with A.I.R. this is the air pump for emission reduction (Not A/C). 343787 LH 353030 RH There is nothing on the parts manual page showing application specific parts for a 396-402 C10-30 Air Conditioned vehicle. If there were it would probably be notated w/AC, C.A.C., or C60. __________________ Tony 71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assm. guide "kit" for restoring the truck from ground up. With assys, the guide accts for 1000s details, OEM identifications & part numbers, written in short order. 700+ images of assm., illust., charts, and points of interest. Much of the info. applies to all 67-72 GM trucks, and to a lessor degree all 67-72 GM vehicles. My build thread, and more on the guide https://67-72chevytrucks.com/vboard/...d.php?t=730025



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