The Stovebolt Site Forums The Shop Area Engine Shop Crack in 350 block...

I got a saddening phone call today from the machinist at the local parts store where I am having some work done. Chris, the machinist, tells me that he found two cracks on the block. Problem is, he has already done the boring to .030" oversize and honed the cylinders for new moly rings.
I asked him if he magnafluxed the block before doing the machining and he told me he only did the areas that typically crack or are known to be problematic?
It cracked in an odd area that he has never seen before. Am I liable to pay for the machine work,and the hot tanking he did 3 times even though he didn't find the crack before the boring? The block is pretty much just a boat anchor now.

Where is it cracked?

On the side of the block. One crack on each side, same length. Just below where the heads mate the cylinder deck. Bout an inch down. Seems like the motor may have sat outside before I got it and had water in the water jackets during cold winter months, froze and cracked? The freeze pugs were not disturbed when I got the complete engine from a local auction for $55.00 Will try to get some pics later this coming week.

See if he will split the cost with you of "sewing" the cracks with threaded, tapered plugs. It's a procedure that's been around at least since the 1940's, and it works.

Find the end of the crack, drill a hole, and thread it with a special tapered tap. Screw a cast iron plug into the hole, cut it off flush, and overlap the next threaded hole into the plug you just installed. Keep drilling, tapping, and installing plugs until you run out of crack. I've done it on many occasions, and the repair turns out leakproof, and usually compression-tight when used inside a combustion chamber. It will definitely seal a crack that has nothing but cooling system pressure against it.
Jerry

Hotrod is right. Have had a few blocks and heads fixed that way through a local machinists.

But it is getting harder to find someone that will do it. It is a little time consuming. But it is reliable.

Hmmm.. never heard of that method. Will ask Chris on Monday about it. IF he is reluctant, will check around to some other machine shops. Thanks again. Brian

Goodson machine shop supply sells the supplies to do it, including the drill bits, taps, and plugs.
Jerry

Stitching is a very expensive process. The shop should eat it.
He should have checked if thats what he said he was going to do.
And why would he say he's not seen it? Of course they can be cracked around water jackets. If they say they are going to check for cracks and are charging for it then, if they don't find a crack, it is on them. A brand new block would be less than a stitching job. Stitching is for large expensive castings.

When you took your block in what did you have on the work order? Did it specify to clean and inspect the block to make sure it was a good candidate for rebuilding? I've seen the other side of the coin where someone all but nails the shop to the cross for doing more than they expected to pay for. Sometimes as they say, you get what you pay for.

May not help much in your situation, but I had a 350 block that cracked in a straight line about 2 or so inches down from the top of the deck.

It was in a pickup that I was driving and needed so I had to the best I could to get it going.

I cleaned the block the best I could, wire brushed the crack to clean it even more. Then I put JB weld on the block.

When I sold the truck 5 years later the guy that bought it drove it another 10 years without any trouble. Even then the patch was holding, he just flat wore out the engine. I'm not recommending the JB weld fix in your case, but the stuff does work well if everything is cleaned properly.

Is he certain it is a crack? I have seen a couple of 350 blocks that had what looked like cracks but were simply a casting mark.

Has the block been pressure tested to see just how long the cracks are? Sometimes the leak will extend beyond the visible part of the crack. I've done several stitching jobs with ordinary taps and steel bolts, but the cast iron plugs are better- - - -less expansion difference due to heat.
Jerry

Try MIG welding up the cracks. Done all the time around here on outer cracks on engine blocks. I know it sounds crazy, but I've seen it work just about every time.

I worked at one machine shop that would JB Weld such cracks, on a clean block it worked fine.

Before any work was done, we agreed that since this was a truck engine, and a used one at that. He was to hot tank the bare block, magnaflux the block to check for possible problems and then we would go from there.
As for wether or not it is ACTUALLY a crack or a casting mark? That is a good question because it is kinda funny looking crack. Has ridges and doesn't look like a normal crack? I will look into that further tomorrow. I do a decent amount of business with this parts store so I would not be against splitting the cost of the work that has been done already, just to maintain a good business relationship.

An easy way to pressure-test a block is to bolt a bare cylinder head onto the block, and plug the water passages from the head to the intake front and rear with small steel or aluminum plates bolted onto the head. Then adapt a garden hose to the water pump hole of that side of the block with another flat plate. Turn on the hose, and look for leaks. You can do it one side at a time- - - -there's no water passage from side to side. I test blocks and heads that way pretty often.
Jerry

Like Jerry said, stitching, or as Gandpa called, cold welding, is a viable way to save a block. Back when my uncles races quarter midgets, Grandpa repaired a cracked Continental 2 cylinder engine that way. My Uncle John raced that car successfully after that, even beating out twin engine karts with it.
Something that does bother me, though, is that he "found" the "crack" after hot tanking and machining the block. Has he shown the crack to you? I'm not trying to say that he's dihonest, but the mention of it being a truck block and finding a problem after doing the work raises red flags to me. Is it a 4 bolt main block? Around here, the dirt track racers will pay top dollar for a 4 bolt main block, and I have heard of a few shops that will sell someones engine off to a racer for the easy money, then say that the block was "bad". That actually happened to a neighbor of mine. They ended up having to give him a new 4 bolt block to replace the one they sold.

Yep, I've got a pretty good stash of 4-bolt blocks, and they're in pretty high demand. I used to scavenge up "worn out" 4-bolt blocks that had been bored .060" oversize and raced for a season or two, usually for free or scrap iron price, and then have my engine machining students use them for practice installing cylinder sleeves. With 8 sleeves in it, the block was back to standard size, and the cylinder material was better than original. It was fun, beating the other guys at the track with their own junk!
Jerry

i would ask you to have the heads bolted on the block before you have it pinned up, if you dont when you torque your heads on it ,it could open up the repair,when installing the pins put a little JB weld on the treads and tighten up,if done right it will never leak water, i have done more than my share of repairing and i didnt want to have problems after spending alot of time repairing cast iron,just my opinion.dan

I don't know what block you ended up getting but if it's a mid '80s "Hecho en Mexico" block, scrap it and buy something on the cheap that has a higher nickel content. IN MY OPINION, the Mexican made blocks and heads are inferior and are prone to cracks due to poor casting procedures and inferior raw materials.

I did see the crack yes. It just looks kinda funny to me? The machinist was goint to take a better look at it today. I say it was a truck block due to the 4 bolt main caps and that is was still bolted to the front frame section when I boiught it, the frame had been torched out of the vehicle and it was a real heavy duty frame. Had king pins instead of ball joints. In the end, it's still just a guess on my part, but an educated guess I feel. I do not kow if it is made in Mexico or not. We will see what becomes of it.? Brian

i found a crack in a 292 block after it was mag'd, cleaned, bored, and honed. i only noticed it after i could see a what looked like a hair of rust starting to form. i took a picture back in and they told me magnaflux won't pick up all small cracks. the location it was in hasn't caused me any problems at all.

I think what i am gonna do is take the block back to my shop and grind the "alleged crack" down to a fine line, clean it as best I can, whether it's with chemicals or mechanical means. Then I am gonna try to MIG weld it seein as how I am pretty proficient with the MIG. I mean heck, what do I have to lose right?? Will keep ya'll posted. Brian

If your going to try to weld it, then a high temp preheat is needed, and you have to hold that heat on it. Use a cast iron rod as filler. Almost better to gas weld it. You can do the pin deal yourself, there maybe some that are inexpensive, but the locknstitch ones are very pricey. The heat is likely to distort it and it will likely need to be bored or at least honed to check it.

Try a few practice beads on a junk block or cylinder head before you attempt to weld your block. I think you'll find that MIG and cast iron don't mix very well.
Jerry

if you try and mig weld it and it doesnt work you will not be able to drill and pin it, then its another block, 350 chevys are everywhere.maybe go back to the machine shop and ask him if they will help you out on machining another block for you.

well, i don't know to much about anything and i have never tried to mig weld cast iron, but i don't think it would be my shot at fixing the crack. i have welded cast with cast rod on arc welders and even with preheat it's a gamble. lots of time the crack will extend as it cools or crack off from it. i think the gas welding would be easier to control. why not try to braze it? that is the old way of doing it. the cast doesn't have to be as hot for the brazing with brass filler as it would for any other type. even then, it's not a sure fix. honestly, if you dodn't have some time on gas welding, i would just jb weld it- it's prob the best shot to work unless you want to go to the trouble of the drilling/tapping stich. whatever you do i would try it on some scrap motor cast first like jerry suggests.

Well, I picked up the block today after work and got it home on the engine stand. Using a 4 inch grinder with a fine wheel, I ground out a small groove in the crack to about 1/2 inch past where I could visually see the crack end. I then cleaned it with Brakleen, air hosed it off, wire brushed the heck out of it with a new stainless steel wire brush.
I agree that MIG is really not the best means of welding cast iron. It is supposed to be down with nickel rod, so I am told by a pipefitter friend whom welds at a nuclear plant for a living.
Atfter preheating the side of the block with a rosebud tip from the oxy/acetylene torch, I tried to MIG the crack closed. IT was going well, except when i finished the bead, I could hear it cracking, and see cracks across teh bead. Cast iron is a funny material, not very stable at all. pic of the welded crack.
I had spoken with the machine shop owner, he had another 4bolt main 350 block that was his sons and he offered it to me for $250.00 if I would let his shop do the machine work on this block as well. He felt bad about not finding the crack earlier and does not hold me liable for the work. I thought that was a stand up thing for him to do. I agreed to let him bore and hone the second block. Paid him for it and took my boat anchor home to try welding it. (I think in the back of my head I already knew it wasn't going to work.)

Actually, cast iron has been welded successfully for longer than any of us have been alive, but it must be done prpoerly- - - -there are simply no shortcuts. It's done with a reverse-polarity DC stick welder and nickel-alloy rod, after preheating the metal. Weld about 1/2" at a time, and peen the weld bead for a few minutes with the pointy end of a slag hammer to stress-relieve the bead. preheat again, weld, peen, etc. until the entire crack is covered. Before welding, the ends of the crack need to be stop-drilled with a small drill bit to keep the crack from spreading. You still might be able to salvage that block by doing the job corrctly- - - -after grinding all the MIG material out.
Jerry

Jerry, if the block were to be welded successfully would the block have to be decked? how about the cylinder bores? thanks

When we're dealing with tolerances in the thousandths, or less where cylinder roundness is concerned, I think it would be a good idea to check for any distortion and correct it. A few thousandths off the deck and a quick hone job would be a minimum, in my opinion. I've seen a demonstration where an inside micrometer is tightened into a cylinder lengthwise to the block just enough to hold its own weight, and when the sides of the block are given a firm push, the mike falls out due to distortion of the cylinder. Heating and cooling during a welding job definitely creates a lot of stress.
Jerry

Jerry has perfectly described the correct method for welding cast iron with an electric welder. The peening is absolutly required and as with all welding the proper rod is esential. Being an old guy I still sort of prefer gas welding, i.e., brazing on cast iron. but I've used DC nickle rod with success too. Forget MIG wleding.

It has been mentioned above but getting it really clean is absolute with either method.

Hotrod Lincoln was correct in my case; I had my 216 rebuilt and insert bearings cut in to it. I got it home, rebuilt the body when I got the parts back from the paint shop and when I got it started there was an 8 inch crack in the left front side of the block in the water jacket about 2 years after I had it rebuilt so I really didn't have a good argument against the rebuilder asking him to correct work he did 2 years earlier. I contemplated welding and JB weld also, doing a Google search I found Lock N' Stitch in Turlock California that sells stitching pins and has tech support to help you all along the way. Peggy has a Tech Tip pending when she gets time to post it as I took pics along the way. The pins actually pull the cast into the pins instead of inserting the pins and them pushing the crack outward. They are very forgiving and you can drill into a neighboring pin and countersink it and run a tap into it and insert the next pin. I can send you a copy of the tech tip in word format with pictures imbedded, Flicker wouldn't let me up load a word document if you need or want to see it before Peggy gets enough time to post it. Good Luck and it can be done. Mine was less than $250. But I got a little to aggressive with a smaller pin and it stripped, so I had to buy 25 of the one size larger pins and that mistake cost me another $100. My mistake and I needed to slow down. After view looks like the crack never existed and it doesn't leak anymore at all. You can also ship the block, bell housing, head, or what other part you want to them and they will repair it for you. The also offer mobile service, I know their website shows a cruise ship repair that threw a rod and they replaced a large segment of the side of the block using that process. Regards, John

that crack off has happened to me several times with my arc welder with the propper rod. i think i may get a little impatient and try too long of a bead before i stop. who knows about mig welding it, i have never tried. with enough heat for penetration a crack would be easy to happen. i do use dc rev pol on my old hobart too. like i said in my earlier post it's a toss up if it works. i'm sure a pro welder would have a higher sucess rate. the key prob is the short welds and peening like jerry suggested. i don't know, i have just had so much better luck with brazing, i don't know if i will ever try it again. i still have some nickel rod. when i found a crack on the head of my flathead hudson, i just jb welded it and it has held up good so far. at $100 a pop for a head gasket i din't want to remove it again to try the brazing.

When welding cast iron like is being considered does burying the piece in sand or thermal blankets help ease the stress letting it cool down slower?

I would be interested in seeing your pics

Thank you

Email sent to your profile email address with the tech tip attached.

Yes, after post-heating the part once the weld/peen procedure is done, burying it in a pile of DRY sand helps it to cool slowly. Putting it in the kids' sandbox after a rain might not be the best idea!
Jerry