Cracked 302 exhaust manifold

[mo-mudder]

Anyone have one of these laying around, just taking up space? I have a massive exhaust leak and thought it was the gasket between the intake and exhaust manifold, right below the carb, but upon further investigation, there's a massive crack in the manifold itself, and instead of JB weld-ing it, I rather just put a good one on there. Anyone?

 

[maddawg308]

Just letting you know, if you can't find a replacement old stock one, there are some exhaust shops that will build a tube exhaust manifold that will bolt right in, based on your cast iron original. Breathes better too. But it is a couple hundred $$$. Just in case you can't find an old one in good shape.

 

[mo-mudder]

Yea, I can actually fabricate my own from some DOM tubing from Summit, but figured I'd just ask you guys first. Plus, I heard that these run better with the factory exhaust manifold, heating up the intake, but I wasn't sure how accurate that was.

 

[hippiedude]

hey I could use one too if there is more than one out there!!!

 

[mo-mudder]

If I do end up fabricating one, would you be interested in buying one?

 

[JasonS]

There are lots of places that make tubular or cast iron headers to fit the 302. Patricks Antique Cars and Trucks sells a cast iron version (may be a modified 235/261); Cliffords sells short and full length tubular header (BTDT), Phillips sells larger diameter cast iron headers nice but $$$. Speedway motors sells a cheap 235/261 header which may be applicable to the 302.
I ran a 302 in a 1/2 ton p/u for ~10 years. Manifold heat is an absolute must when below 32F. The exhaust heat kit that Cliffords sells is just about worthless. I added a water heated plate between the manifold and carb which did help.
Shouldn't be that hard to weld up the crack. Clean the crack down to CLEAN metal and weld up with 99% nickel rod.

 

[mo-mudder]

Do I have to use a nickel rod, or can I just use my regular rods, but just pre-heat the affected area?
I was looking at alfaheaven, and they sell an intake/exhaust manifold set for $150. I may just go that route if it looks to be pretty bad.

 

[davesgmc]

The nickel rod will work much better on that cast, regualr rod is relaly ahrd to flw into cast steel or iron. You can braze it together to hold it if need be then use an arc wlder with a nickel rod. I have welded engine block, heads, etc many times and it works great. it is easlily machined afterwards too.

 

[hippiedude]

Do you have to preheat the manifold ?? Or just clean and weld ??

 

[davesgmc]

depends on how htinck the part you are welding is. if its approx 1/4 inch or thinner you may not have to put heat to it before welding, if it thicker you may want to heat it to get the prope penetration. Heating will allow the filler you are using to penetrate all the way through. If it dosent go all the way or just about all the way through it will crack on either side of the weld again eventually. but you dot want too much heat and warp it or burn through. the best is to have it bolted to the head or a strong steel table while welding to try to keep it from warping.

 

[mo-mudder]

You know, my neighbor pulled a straight-6 out of a 71 Nova a couple years ago, and just set the engine aside, as he was transplanting a 472 into the car. What are the odds that the exhaust manifold from that car would fit the 302? Everywhere I look, there's stuff that mention the 235, 261, and 302 in basically the same family. What modifications are necessary to put an exhaust manifold from a 235 or 261 on to the 302? Maybe a little port matching?
As you can see, I'm not terribly interested in making sure that everything is original, I just want to get my deuce on the road in a less-than-really-noisy condition.

 

[hippiedude]

I didn`t take into consideration that it might warp...Bolting to my welding table would work..never used nikle rod before .. how easy is it to weld with ??

 

[JasonS]

The nova will have a different style engine (194, 230, 250, etc). The GMC engine is 1-7/16" longer than the 235/261 chevy so the (one piece) exhaust manifold will not fit. I think that the two piece cast iron headers can be modified to fit the GMC. You can get the correct cast iron headers from Phillips Performance for ~$450 or get tubular headers for ~$180 (ten years ago).
Cast iron isn't that hard to weld. The biggest problem with exhaust manifolds is that they are very contaminated. You have to grind off the top layer of dirty iron. I used an AC welder. I had to turn up the power to get decent penetration but this caused some undercutting so I had to keep the arc very short. You really need to use the Nickel rod. You can use TIG if you have clean cast iron like a head or intake manifold.

 

[maxim]

I broke the cast iron tab off a C-J transfer case that hold the shift lever. I cleaned the area well and "V" cut with a grinder about 45 degrees at the joint to get some area of clean metal. I used nickel rod and a light touch as not to get it too hot. Clamped the tab as well as I could. Not being a pro at this and what you would call a "farm" welder, using a standard Lincoln stick welder I was very pleased how it turned out and it is holding so far. I would suggest to try it. Experiance will be gained no matterthe outcome.

 

[M543A2]

I did have one, but would have to hunt through all of the parts piles for it if you want it. The biggest mistake people make with these long exhaust manifolds is tightening the retainer bolts too tight. They need to be able to move lengthwise as they heat and cool. Hold them too tight, and they will break. That is why the big diesels and 6602 engines have expansion joints in them. My M135 kept wiping out the exhaust gaskets because of the expansion amount. I made copper gaskets and stopped that problem, but I can still see where the manifold shifts. Our best solution is to not use gaskets at all, being sure the surface of the head and manifold are true and straight.Don't overtorque the bolts to allow things to move. For me, an experienced welder, manifold welding has always had mixed results. Some weld well, some do not. I tried it on a 6602 and it broke again. We did it on an 1155 Massey Diesel, and it held.
Regards Marti

 

[hippiedude]

Thanks guy`s that helps alot... M543a2 if you are digging around and find it PM me as i`m trying to keep my M211 original as I can thanks.....

 

[n1bnc]

If you need a replacement that would be stock, try Alpha Heaven.

 

[hippiedude]

Thanks I will...

 

[mo-mudder]

Well, I got the manifolds off today. Took of the intake and exhaust together, along with the carb and about 10 inches of the tailpipe. Heavy bugger! Good thing I cut trees for a living and am used to lifting heavy stuff in peculiar positions. Decided to go ahead and just go with the stock replacement intake and exhaust from alfaheaven. Got the combo for $150, plus shipping. Figure that'd be the easiest and cheapest option right now.

 

[hippiedude]

Thats not a bad price...I will have to check them out....