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Old 12-22-2009, 03:59 PM
quadrajunk a name earned
 
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Repair Cracked Cast Iron Intake Manifold?

The machine shop just called me and said they found two cracks in my 1970 Pontiac intake manifold. I thinks it's made of cast iron? They told me one crack is in the center divider and the other is in a bolt hole pointing outward. I haven't seen the cracks yet so I wanted to ask can a cast iron manifold be repaired and if yes how so; welding? Will the repair hold or is it a gamble?

They told me if the first crack continues it will create a vacuum leak. They didn't seem concerned about the second crack.

Thanks,
BT

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Old 12-22-2009, 05:25 PM
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Myself I wouldn't trust it myself. Iron Pontiac intakes are not hard to find and in my opinion I would replace it.
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Old 12-22-2009, 05:25 PM
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Yes it can be welded by a GOOD welder but that can be pricey. See what your machine shop says for a price to fix it *** correctly ***. I just looked on Ebay...there are a bunch of intakes on there that would fit your application, cast and alum..
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Old 12-23-2009, 12:14 AM
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Chunk it and get a aluminum intake. Few people can properly weld cast iron. The only time I would bother to have it done was if I was dealing with a rare piece in a restored vehicle such as a 1969 chevy 302 block for example.
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Old 12-23-2009, 02:51 AM
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Cast iron can be easily brazed, if you have a oxy/acetylene outfit at home you can do it yourself as long as you preheat it...barbeque works fine. It really depends on if the crack is accessible or not and how much it is worth to you...a machine shop would likely charge $50-$100 depending on where and how bad the crack is.

New intakes are cheap.
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Old 12-23-2009, 09:15 AM
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I had to have my 400 block repaired, outside starter bolt hole had busted out and some goober had welded it up solid,didn't notice till I had already had it to the machine shop.Took close to 2 hours to weld up,with the cooling time,$50 at a local welding shop.
I have done a little cast welding,when I was in HS,and did not find it that hard,with proper preheat,post heat and cooling,It is no more difficult than welding mild steel, Its the prep work that makes it tedious and time consuming IMO.

Shane
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Old 12-23-2009, 11:20 AM
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Quote:
Originally Posted by DoubleVision
Chunk it and get a aluminum intake. Few people can properly weld cast iron. The only time I would bother to have it done was if I was dealing with a rare piece in a restored vehicle such as a 1969 chevy 302 block for example.
I had that very thing done a number of years ago. To make a long story short I was in a jam and needed an engine after blowing up the original 307 for my 70 Nova. A friend of mine knew someone who had an original "DZ" 302 short block, that needed an overhaul. I bought it for $150 ( this was 1972). When I picked it up we noticed that it had been run with a blown head gasket for some time and there was a valley between two cylinders. We completely disassembled the engine and took the block to a well respected welder. He placed the block in his oven to preheat it then gas welded the crack with a nickle rod and dressed it flat with a file. Upon reassembly we used GM steel head gaskets and glued fine soft copper wire around each cylinder of the head gaskets. We reassembled the engine with new rings and bearings. I drove that engine in the Nova for another 5 years before I sold the car. The new owner must have been really surprised when he tore that engine down. A number of years later I realized what I had lost .

Vince
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Old 12-23-2009, 05:33 PM
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I talked to the shop today and they told me the intake manifold is usable as is but if the vertical divider crack spreads to the horizontal divider then a vacuum leak occurs. Cost to plug it is $100. I am not sure what plugging is?

I was wrong on the other crack location. It's on the outside barrel casting and does not go through to the inside. The shop didn't seem too concerned about this crack and told me to JB Weld it from the outside.

Since I have a second Pontiac factory intake I will use the second one.

BT
Houston, TX
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Old 12-23-2009, 09:17 PM
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plugging

Plugging is a method that uses a series of overlapping drilled holes, taper tap and taper plug one set at a time to repair cracks. I haven't seen it used for the last 50 years.
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