The Stovebolt Site Forums The Shop Area General Truck Talk Exhaust manifold crack

I recently removed the intake and exhaust manifold off a 235 I want to put into my 3100 1/2 ton and discovered a crack in the exhaust manifold. I know how good JB Weld is but can it stand up to the temp of an exhaust manifold? If not is there something else that can be recommended?

I cracked a head on a ford big block and used jb weld to fix it. Lasted for a few years before it broke the jb weld down and I had to do it again. I really had to work at it to clean it up enough that it would stick to it. Id say go for it as a temporary fix, but not long term...

Jeff

jersey boy,

My vote would be nay! I think the temps seen by the exhaust manifold plus the expansion and contraction of the manifold itself would doom any goop to a early death. My first choice would be to replace it...Fentons or another stock unit. My second choice would be to have it repaired by brazing it! A welding repair should probably be followed with a surfacing job.

Stuart

I have welded up plenty of them with my MIG without any problems.

Another option: I see these on e-bay all the time. Search under "235 Chev".

I,d give it 2-3 minutes. They are often welded but one that is that plentiful I would find another one.

51' Rust Bucket, what wire do you use in your mig to weld cast iron? Brazing or Nickel rod would be the ticket,just my opinion.

I use plain old .030 steel wire. Years ago I broke off one of the stud flanges on Nova's manifold and was in college (which means I was broke )Couldn't afford new one so I broke out the welder. It was just a little 90amp century welder cranked up all the way. worked like a charm. I also rigged up both cylinder heads on my old 400 that cracked around the steam holes. They say necessity is the mother of all invention. Ha! More like you broke it while street racing and better fix it before your dad finds out, or your goose is cooked!
I don't know the proper way to fix cast but I know what worked for me in a pinch. Now I'm alittle more financially stable so I'm able to just chuck em and replace em.

Funny, I've been welding for 30 years and I've never tried welding cast with hard wire because everyone said it could'nt be done. Now I've got to try it just to know pre-heat and post-heat on cast is critical.My intake on my 235 is cracked and I've nothing to loose.

I was always told not to do it either. I don't know the longevity of expansion/contraction over a long period because I changed motors in that car more than I changed my underwear.

The exhaust manifold that I welded lasted for quite a while until I saved up enough for hedders and new exhaust.

If you have ever dealt with a small block 400 you know how the heads crack easily between the steam holes and the head bolts. I remember finding a crack in each head. I couldn't afford to replace them of have them fixed professionally. I just ground a 'v' along the crack and gave it a good tack, ground it down and never found any antifreeze in the oil. I guess when you don't know any better you'll try anything.
Do you know why you're not supposed to weld cast? I too have heard not to weld it, but no one seems to know why or what happens.
This has been probably 10-15 years ago. Actually, there are a lot of things I used to do back then that I wouldn't do today Gone are the days of duct tape & coat hangers!

51 Rust Bucket,

The carbon content of cast iron is the bug-a-boo! When you weld it and melt the parent metal, the carbon is displaced and ends up right smack dab in the weld zone in the form of Martensite.

Martensite puts Kryptonite to shame on a hardness and brittle scale. Arc welding rods for cast iron are usually 'pulse' rods that sort of turn on and off in an attempt to keep the weld zone as cool as possible. Preheating the casting, welding and postheating allows the carbon atoms to migrate back to where they belong instead of being concentrated in the heat affected zone..HAF.

I have a bench grinder stand at home that someone welded back together with a wire feed and steel wire. It looks like hell but hasn't fallen apart yet...sort of like your cylinder heads. If actual strength of the weld is important, the proper welding procedure must be followed...you can't fool those carbon molecules for long.

Stuart

Good call Atomarc. I've brazed alot of cast with really good results and the Ni-rod works well also. I can't wait to get home tonight and try the hard wire on cast just to see. The other thing to mention is the part really needs to be clamped down on a straight metal table as the parts really will pull away in strange directions. Slow cool down with insulated fiberglass blankets will usually stop any cracking and I usually will peen the weld area to relieve any stress areas.

I double checked with the welder who did my manifold and he told me the following:
1.Dimple the ends of the crack with a small drill bit. 2.Preheat to 400 degrees. 3.Use UTP FN 85 cast rod. 4.Peen with an air hammer between passes. 5.Wrap in a blanket or bury it in vermiculite to cool.

Curt B.

Thanks for the info, I really don't remember if the welds took any extra effort to grind down or not.
Since there actually is a real way to weld up cast, the starter bolt flange busted off the bellhousing on my '55. I just might try braizing the piece back on instead of buying a new one.

Thanks again,
Scott

My experience with mig welding has been very good. No special preheating or slow cool down used. The only failures were in an area that was spider webbed and the many tiny cracks filled with carbon from the exhaust. This usually was under the metal shield used to duct heat up to the air filter housing and it wouldn't take brass or nickel either. On clean grey iron, like welding a flange on for a split manifold, just strike an arc and weld away--no short beads and cooling necessary and just plain old wire. Cut a junker in half, vee the ends to grey iron, and practice; I think you'll be pleased.

It's nice to know I'm not the only one who has tried it!

Vermiculite---OK, kitty litter will work, or so I have been told--(may be the same thing).

You are just trying to make sure it cools slowly after the welding to prevent cracking.

You need to find the OLDEST muffler/welding shop in Farmington and just maybe you'll find an old grey haired guy to weld it up. Short of finding that shop, I'd be shopping on ebay or this site for another manifold.

Rust Bucket ,you are not alone ...lol
several yrs ago I had an operator at work raise a molder head (this head is abought 16 feet long) with onna the jack screws that raise the head out to lunch an snapped off the cast iron main beam on the one end....bein 2am and the Molder in desperate need of being back in-service ...we all looked at each other an tossed it back an forth for a fix ...knowin that a replacement beam from Weinig in Germany would be ...WHO KNOWS HOW LONG TO GET ONE ...I told my maint guys to Mig it what the heck ???? worst we could do is mess up a already messed up part??...well after a pile a wire ...now this was a pretty good size beam ....it was back together ...an to this day ..it is the same way ..there is a new beam in the parts shop waitin to go on that molder...but it aint never broke so why change it ?...so when my one Rams horn small block chevy exhaust manifold in my Bolt had a crack in it ? I didnt hesitate to Mig it ...still works just fine to this day .
All we did was V it ...an hit with the Mig ...an let it cool down on the bench for a few hrs.

jiMerit is phycic, how did he know I'm 70 with grey hair (where there is hair) and been welding since I was 15?

Spooky.................

you could find one of a 235 for 20.00 or so