Hello  I have  std bore 312 block that has been freeze cracked. I don't know why I saved it (30 years) but I did. The crack is about 2 1/2" long on right front edge (flat part) just before where right side starts. It is a very fine crack, unless you hot tanked it or really looked hard, probably would not see it. Any way, does any one here had any info or advice on fixing it or junking it? I have researched a little using stitch and lock. They make it look easy BUT I have been told that is easy to break taps off, that where trouble starts.  It will cost over a hundred dollars for parts if nothing goes wrong. Iam thinking it is not worth risk and sent it to China. Bill  Oregon

A good welding shop should be able to weld cast. Reason I mention it is because many years ago the shop I worked in used to take the 250 scruby 6 cyl integrated head to Indy Cylinder Heads in Indianapolis. They were very prone to cracking in the combustion chamber, and at the time expensive and hard to find. We would get them back looking like new.
But, after saying that, welding cast with nickel, stainless rods is pretty much a lost art. In the past... I made a repairs on a 4x4 front differential ring gear carrier by welding up an oblong hole where the spider gear pinion shaft went through by brazing it. I have also brazed up external cracks like you have in blocks and brazed exhaust manifolds back together that were in 2 pieces.
In todays world that wouldn't fly and people would think you were nuts to even mention it.

Today, if I had a repair like you have I would use the lock and stitch method. I know you said you were afraid of breaking the tap, but as long as you take your time, use the correct drill size, watch your pressure while tapping, and your tap stays nice and sharp you probably have nothing to worry about.

Anyway. Just a thought if the block is worth saving otherwise.

My .02 worth.

Dave

If there is a shop in your area that repairs industrial castings you might let them have a look at it. They will magnaflux it to determine the extent of the crack and give you their opinion of whether it's fixable. I had a shop fix a couple of flatheads 20 years ago and they're still going strong. It sounds like it's in an unstressed area so you might be good to go.

As Dave C says, it is feasible, but before you precede, best to check closely for Main bearing journal area cracks. Unfortunately, cracks are fairly common, in 312 blocks, especially if the block is a 1956 casting, due to a spec error in main bearing torque, that was published in manuals!.. And over zealous rebuild torque settings also contributed to cracked blocks or stripped main bearing threads.. Good luck!     


Paul

the harnand chain lock was used to repair early d8 dozers 2u  trans and steering clutch aria a,large casting.the co that did these repairs did hundreds hear in bc,we also repaired engine blocks. that had asuply of the cross chains which went into inter connecting holes,these wherpeaned into place every2in of crack; then pip plugs in-between so no leakage. worked great if we got there before some welder tried 1st. cast is easy to drill if no one is near trying to weld. email harman chain lock repairs.you should get a idea.
 if the block is good other than the crack should be repairable. crack in rear main aria is not repairable

just went to google and found a site which shows the process under cast repairs block and chain system  or harmony chain lock cast iron repairs

Thanks for replies. I will ckeck out chain-lock type repair. I wire brushed cam bearing  bores to main bearing saddles noting showed but I have not hot tanked it yet. Bill  Oregon

I’ve been successful at stick welding external freeze cracks in cylinder blocks using nickel rod.  The blocks do need to be cleaned first and a little preheat around the cracked area does tend to help the rod melt to the cast a bit easier.

Lorena, Texas (South of Waco)

nickel works some times,there are lots of cast rods out there some work some do not,but all make the welded aria hard and the chain lock won't ever work as you need to drill the maney holes. the experience welder tells me the main isue with cast iron is every casting has different content and nickel will work ,the next bock or head won't. peaning the weld helps as does slow cooling.due to welding it pulls the welded material, cast iron is brittle,peanigdecreases the aria so crack does not reaper