GMC 302 fatal flaw

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Re: GMC 302 fatal flaw

Post by Joe Gopan » Thu Feb 02, 2017 6:55 am

Good ideas, might work best on new exhausts, used are usually have advanced erosion.
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Re: GMC 302 fatal flaw

Post by Dr Deuce » Thu Feb 02, 2017 8:51 am

There are a few different ex manifolds.

If you look at the back side in the middle, you will see that they tried different ideas/design right in the middle I assume for thermal expansion.

Also, the early manifolds had one header pipe mounting behind the manifold which is somewhat difficult to install the bolt in. Later ones had the bolts spaced such that one faces towards the fender so that the 3rd bolt is not behind the manifold.
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Re: GMC 302 fatal flaw

Post by radarsgunner1 » Fri Feb 03, 2017 6:08 pm

Rex Ward In England has new exhaust manifolds. Their supposed to be modified to prevent cracking. I've had one in my gmc for two years and 3500 miles. I think it was 350 euros.

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Re: GMC 302 fatal flaw

Post by USMC 00-08 » Fri Feb 03, 2017 6:30 pm

Could you post pictures of that manifold?
1952 M135 W/W #5314 - Reg. #41143868
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Re: GMC 302 fatal flaw

Post by G506 » Sat Feb 04, 2017 4:21 am

Dr Deuce wrote:
The Chevys have a full asbestos donut here that allows movement so as not put pressure on the intake-exhaust manifolds.
Steve, really sorry to hijack the thread; I am in need of the donut, and this side of the Atlantic they seem to be non existent. Any ideas as to where I could find one?
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Re: GMC 302 fatal flaw

Post by Joe Gopan » Sat Feb 04, 2017 4:40 am

Remember, go to NAPA and buy the manifold set by Felpro. The 302 set is different than WWII 270 due to the larger intake Pilot holes in the intake gaskets. OEM GI Issue gaskets do not seem to seal and last as long as the 40's-50's gaskets in this application. The 3 Piece GI Issue GM Manufactured exhaust manifold is virtually trouble free due to it's two slip joints and sealing rings. They are like hens' teeth to find as they are 45 years out of the system.
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Re: GMC 302 fatal flaw

Post by Dr Deuce » Sun Feb 05, 2017 2:21 am

RE chevy donut:

I buy mine at a good auto parts store.

If you have the original chevy dipper engine, the 1940 thru 46 civy engines use them.
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Re: GMC 302 fatal flaw

Post by Joe Gopan » Sun Feb 05, 2017 5:13 am

Those of you who attempt to cure an exhaust leek by continually reefing the nuts will discover that your manifolds are warped and that the gasket surface on the head is eroding. Only cure is taking the worn head to a machine shop, same for exhaust manifold.
Back when surplus M-211s were numerous at volunteer Fire Departments, I averaged an Exhaust manifold sale a month and the NOS ex manifolds could be resold for under $200.00. Not so any more.
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Re: GMC 302 fatal flaw

Post by Jeeps4Brains » Mon Feb 06, 2017 6:01 am

Are you saying the exhaust sealing rings are hard to find? You mean these: http://www.ecklerstrucks.com/gmc-intake ... -1959.html
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Re: GMC 302 fatal flaw

Post by Joe Gopan » Mon Feb 06, 2017 6:40 am

No.
NOS GMC Exhaust manifolds for 228 CID thru 302CID are very scarce, both thru GM and Surplus. I have the rings,NOS, both large and small that I include with NOS Intake Manifold sales for 270 and 302.
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Re: GMC 302 fatal flaw

Post by Joe Gopan » Mon Feb 06, 2017 7:53 am

And, remember.
Not as much as a fatal flaw, age and diligent maintenance are also factors.
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Re: GMC 302 fatal flaw

Post by G506 » Sun Feb 12, 2017 1:04 pm

Dr Deuce wrote:RE chevy donut:

I buy mine at a good auto parts store.

If you have the original chevy dipper engine, the 1940 thru 46 civy engines use them.
Hi Steve,
many thanks, Im guessing that is the metallic donut? It is the Asbestos ring I was hoping to track down, but here in the UK the Health and Safety folk have a heart attack as soon as Asbestos is mentioned :D
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Re: GMC 302 fatal flaw

Post by USMC 00-08 » Sun Feb 12, 2017 3:09 pm

Is this what we are talking about?

https://www.napaonline.com/p/FPB60986

I have used them on my M135 original exhaust system and they seem to work well. They are sintered metal.
1952 M135 W/W #5314 - Reg. #41143868
1952 M135 W/O #4984 - Reg. #41143???
1951 M135 W/O #3194 - Reg. #41122836
1951 M135 W/O #556 - Reg. #41121215

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Re: GMC 302 fatal flaw

Post by Dr Deuce » Mon Feb 13, 2017 2:38 am

I can't really tell from the picture.

If it is 1/2 convex and the other side is a ring that will go into the ex manifold, then yes.
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Re: GMC 302 fatal flaw

Post by Dr Deuce » Mon Jun 12, 2023 8:50 am

I have had a set of manifold gaskets made from copper.

I have not tried them. They were water jet cut.
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