I recently found a huge crack in the exhaust manifold on my '69 Chevy pickup. I can replace it with a used one for around $70 or a new reproduction at $110 or I can try to repair it. I asked my favorite welder and he does not think welding it would provide much long term success. I also have some crack repair stuff from POR 15 which is a two-part mixture which is supposed to be able to withstand 1400 degrees and is specifically made to repair exhaust manifolds. But can any such material be expected to withstand the expansion and contraction an exhaust manifold goes through? If I recall correctly, the name on the package is FlameProof 1400. Does anyone have any experience with this or a similar product?

I'd agree with your welder. I had a broken one on my Son's 71 Blazer. I took it off, welded it, and broke it again putting it back on. I can say without a doubt that my welding was a perfect failure.

It can be brazed but if you don't have access to the equipment it not worth it. I don't mean a torch you need a way to heat the whole manifold to 1000deg and work from there.

I used to have good luck (arc) welding cast. I used what was know as 'super missle weld' rod. Weld a small amount at a time to ovoid getting things too hot.

I have had several welded and split (for I6's). They were fine. You just need to find a welder that has the stuff to do it.

Here is a link to a demo of someone using a Henrob torch to weld cast iron. It should be quite informative.

http://www.cut-like-plasma.com/info_welding_cast_iron.htm

If you are a welder and have equipment go to a reputable weld supply shop and ask for welding rod specifically for welding on cast iron - there is a special rod.

It you don't have the equipment, any good welding shop should have some special rod on hand. Years ago I had a 2-1/2" ramhorn manifold ('64 Vette) repaired at a welding shop and had no problems with the repair. One of the 3 ears where the the studs screw into was broke off and gone. They "built up" the area and dressed the shape on a bench grinder to match the shape of he other ears. They did not do "machining" so I drilled and tapped a new hole. They suggested that I redo the hole from the start. Never had a problem with the repair for the few years that I had the car. Too bad I still don't have the car.

Only problem with any repair though is often you can find a replacement part for cost of labor. Shop rates are out of this world! I would reccomend finding a replacement manifold for your situation. I provided the example for those the may need to rescue a "rare" original manifold where the manifold cost will far exceed 1/2-1 hour of labor.

No shop rates are involved, I'll do any work required aside from the welding if I go that route. My welder buddy would use a specific rod, (high nickel content I believe) but he says welding cast iron is tough enough without having the added problems of it being an exhaust manifold which means the iron is full of junk (exhaust residue, carbon, rust, etc.) and has to expand and contract a lot due to the heat they see.

I think I'll pull the manifold and try the FlameProof 1400 repair goo I have have and if it doesn't work I'll simply replace it with a good used one. I'm interested to see if this stuff works as advertised anyway.

What really baffles me is where the crack is. It is about an inch above the exhaust pipe flange on the rearward sideand runs horizontally for about an inch. When the manifold is cold, the crack provides an opening about a 1/16" wide! I just can't see the manifold getting much mechanical stress in that particular spot. Maybe the exhaust system is too rigid and isn't providing enough wiggle room for when the engine rocks from side to side?

When I get around to this project (may be a week or more) I'll report back with my results.

If you choose to repair your manifold, check the fit before you install it. Manifolds crack because they "shrink" with age and bind on the endmost bolts or studs. The fix is to drill out the holes in the manifold so they have lots of clearance around the fasteners to accomodate thermal expansion and contraction. Also, manifolds should be just tight enough to not leak. That way they can move around without a lot of stresses. Welding cast iron is not that difficult ; there is stainless steel arc welding rod that works nicely. A brazed repair will work ok if you do not drive for extended periods at full power.

This is what I heard from a friend who works as a machinist for a large machine manufacturer: Cast iron can be welded, but it's important to heat the whole part to the correct temperature (whatever that temperature might be). The material is brittle and even if the weld looks good, it can develop microscopic cracks around the seam due to the expansion caused by the welding. He said that the heating and cooling must be controlled, but that welding cast iron is a crapshot even when done by a pro and only time will tell if the repair was sucessful or not. You also have to fill a lot when welding thick parts, and the difference in material properties can cause cracks later on.

I stick welded a 440 mopar block with it in the car, and upside down. It's been running consistant 11.2's for a year and have not had it crack again. I have also brazed a few manifolds with luck, just use the torch to preheat it a little and weld it up.

geez louise, there must be a million of 'em in the wrecking yards, eh?

geez louise, there must be a million of 'em in the wrecking yards, eh?
Ha, walk in any junk yard around here and ask if they have any big blocks and they laugh at ya, either that or say "I wish I did".

When I worked in a local job shop, we used to repair them a lot. I would grind out the crack and heat the manifold with a rosebud torch. Then I would weld it with stainless wire and then heat it again with the rosebud and let it air cool. Never had one returned.

I think Rich means a 400 small block.

Wouldnt the manifold be the same all the way up to the 80's? I would think you could easily find another manifold for cheap. The only problems I could see is if they had A.I.R tubes on the manifolds.

I think Rich means a 400 small block.
oops you're right Leo :o I don't know why I was thinking it had a big block. Guess I was getting it confused with my 70 CST.

Maybe the exhaust manifolds are hard to find because it's a pickup :confused:

Rich,

we have cast parts welded in the elevator trade and have had very good luck. The welder we use heats it up red, and welds it with Nickle rod and let it cool slow. I saw someone mention super missle rod, thats good stuff also.


Rocky

Been awhile since i've seen a 67-72 truck with manifolds still but from what i remember they're different then the 73up. Theyre basically a rams horn with a turned back exit. Also these trucks kept the short water pump longer then cars so a 69 should have the exhaust mounted alternator.

You'd think there would be lots of these in junkyards but yards just don't keep these old rigs in them anymore. Also everybody thinks theres lots around so they dont bother to save the parts they think are common.. then you go lookin and find they arent so common.

My manifolds on my 70 cracked years ago, didnt have any good replacements around so they got replaced with headers. I think this probably happened alot. After all the 72s are 34 years old now.

What condition is the iron in? I've seen some of these manifolds "crystalize". If thats the case there isnt much good to weld to.

The iron looks good. As I said before, I already have a source to get a replacement used one for $70 shipped or $110 shipped for a new reproduction. I still haven't made up my mind how to go about it yet.

Just got done on Friday screwing a used one on the RV 'cause the original cracked. I saw new re-pop ones for $80.00 plus shipping. Figured if a used one held up for 30 years it was less risky to put on than a new overseas casting. Didn't want to do it again. The right one is sort of pain to install in the GM 3500 van. No room to work with all that AIR stuff.
Weird thing was I removed it off the block at the junkyard. Had to elongate the outer mounting holes to screw it on my head/engine. Just couldn't start all the bolts.

John , that stuff of having to enlarge the end holes is normal for an old well used manifold. When the engine is run at fairly high power, the manifold can become red-hot and has to expand a lot. When it is that hot, it is very weak and the expansion forces are countered by the bolts, particularly the endmost ones. The result is that the manifold yield and becomes a bit shorter. If this happens often enough, the manifold binds on the end bolts when cool and gets enough tensile force in it to crack the manifold. So, the moral of the story is open those end holes and avoid overtorquing the screws that fasten the manifold to the head.

We tried having one on my daughters Tarass welded because all of the ones at the wrecking yard were cracked in the same place. Lasted about 4 months, they cracked right next to the weld. We got a replacement, installed it and sold the car, that was the straw that broke that camels back.

try welding it with a stainless rod like 308 or 316L, don't forget about the pre-hrat and post heat!!! the high nickel content in stainless has a better crack resistance.

If you go the putty route, you might check out Pyro-Putty 2400. I just tryed some this weekend on a Kia manifold, and so far it's still holding.

I bought it here : http://caswellplating.com/aids/pyro.htm

A quick follow up. I pulled the manifold last week to use some high temp crack filler (kind of like JB Weld but for high heat applications). Well, once I cleaned off the paint and a little rust, I found that the crack went almost half way around the manifold and the iron in the area of the crack was crazed and could be chipped off! It must have gotten really hot at some point.

I already got a used one and will clean it up and install it this weekend. Now I just need to find that crack in the manifold on my MR2.....

Hi actually it's an easy fix as I have done many. First of all sand blast the manifold to get rid of rust then put it in your BBQ on high heat for about 20 or 30 minutes to heat it up all at the same temp. Then use your oxy acet torch and braze it with brass on the outside and inside if you can reach in there. Let it all cool slowly by air. Then you can grind off the excess then hit it again with the sand blaster as then it all looks uniform. Good luck with the used one.