The problem I've found with trying to braze up something as large as an engine block is keeping the heat, tries to run away.......if you get the block hot enough to correctly braze you'll need to have the block checked and re-machined after the brazing job.
Make short welds with the best rod that money can buy.  Peen immediately after each weld to keep the weld from shrinking away from the block and cracking where the weld meets the block cast.  After you get the five or six beads (length of the crack) ran grind the weld , even smooth, to check for pin holing.....as mentioned the crack will hold trash and the welding will draw it up into the bead.  If you have  pin-holing grind it smooth and run more beads down the center doing the same peening and cleaning between each bead.  May even need to run other beads down each side of the center bead.  You can readily tell when you have good clean bonding. Peening drives the weld into the grain as well as keeping shrink to a minimum, as in ....stress relieving.  Check out Eutectic and other major brands for specific rod for the job.  The one  I like....you can even weld bearing races together....break them with a hammer and they won't break at the welds.  I'm retired and my memory ain't that good anymore......seven, eight, maybe even ten years since I've done any serious cast iron welding.  Do your homework. At two and one half inches long the crack should be an easy and quick fix.  I'd still use block sealer as an added precaution. . And, one you start, finish the job, while you have heat in the area. d

I had a cracked water passage on an engine block. I found a block repair epoxy that is used for boat motor repairs. It worked great. I used a grinder to hog out the area around the crack so I could get a good bite on the metal. Worked that way for years. Sorry I can't remember the name of the epoxy but try a local boat shop.

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

I'd be tempted to braze it

I've never had much to do with cast arc welding, but if I recall my limited training in that area, other prep things to do are these. Try to ensure the area does not have water in it & is clean. (oil or water will likely cause porosity)   Then examine the crack carefully, use a magnifying glass if needed, & then drill a small hole at both ends of the crack.  This is supposed to help avoid further migrating of the crack. Also, avoid any sudden chilling of the welded area..  Goodluck   


Paul

I've welded lots of cast iron over the years, from engine blocks to transmission cases, even a lathe saddle that was broken in half.  Eutectic makes a good rod specific for cast, the last I bought was $200. a pound.  Clean the area good, grind the surface a little to get to clean cast; I doubt I'd vee the break seam since you might go through.....likely cracked in the weakest area on the block.  Pre-heat; I usually spit on the area, when the spit bounces off instantly it's ready; the welding process will then keep the area sufficiently heated.  Use small rod, say 1/16", weld in 1/4" to 1/2" lengths, peen immediately, wire brush and make the next weld.  You'll know if the casting is good or poor by the forming of pin-holes and popping in your welds.  The good Eutectic will bond it up, though, I expect.  Then "glass"  the block....may even have a better block sealing chemical process nowadays. Don't buy that cheap-asp ni-rod....results are like the difference between night and day.  And, the one worry I'd have is blowing through and making a big un-fillable hole.  Good luck

Epoxy may be an alternative to welding. Several years ago I was interested in a V16 Cadillac that had a cracked block. I found a place in Portland that would have probably been able to repair it. The deal ended up falling through so I never pursued it further. Unfortunately I also lost the company info that would have done the work. I'm sure they'd turn up in a internet search if they're still around.


~DJ~ AKA "Bleach"
1956 Ford Fairlane Town Sedan 30K original miles

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

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)

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

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