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I picked up, some time back in the last couple of decades, a 1969 Reinell 19' boat with the "140" Mercury engine and outdrive.  This is, of course, the old Chevy II/Nova cast iron, carbureted four cylinder.


I attached the coolant lines to the outdrive, got good flow through the system, and fired it up in the driveway, and immediately got a bunch of water in the bilge.  Inspection revealed a crack, perhaps 3 1/2 to 4 inches long in the side of the block, directly under the intake manifold on the "driver's" side.


Crack repair in cast iron is not something I've ever attempted, so I'm asking opinions of some who've done it. 

Of the options available (welding, epoxy, drilling and installing threaded 'plugs', and block replacement) what's the best route?  


I think I've got around $300 invested in the whole shebang, so if I had to scrap it out, it's not a huge loss, and I could still sell it off in pieces.


Opinions?  Options?

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Rocket Doctor...I've been sidelined with several HD video projects involving products and installations, sorry for the delay.  I have a good deal of experience at restoring castings, mostly from work with vintage and obsolete parts.  Personally, I TIG cast iron repairs, as the heat affected zone (HAZ) is narrow to the margins of the weld.  I have fixed large castings and smaller ones, with several projects presented at the magazine. 


Here are some videos for your review.  The actual block repair is at a local CAT repair facility and performed by its staff.  The 2nd and 3rd videos are yours truly doing TIG repairs on cast iron:


In this HD video, a damaged Caterpillar engine block gets repaired with TIG welding process and Weld Mold Company 700 and 750 filler rod. See the block fix that saved thousands of dollars, performed on the shop floor at Brad Falin's heavy equipment repair facility, Fernley, Nevada.
At the 2011 Midwest Willys Reunion, Moses Ludel presented details on TIG welding iron castings. In this video you will discover how GTAW-TIG process restored a large iron axle casting.
Sometimes a gear or transmission case is damaged and obsolete. In this slideshow, Moses Ludel demonstrates how to TIG repair a gear and broken transmission case.
The primary challenge with cast iron welding is the iron base metal's inability to expand.  Gray, non-ductile iron like your block will not expand and contract well.  A specialty filler rod must be used to compensate.  I have used Weld Mold Company's 700 and 750 series rod as shown in the videos.  This is the best material I've found, as it forms graphite and allows cool down without contracting and cracking the casting adjacent to the weld.  It is also an improvement in tensile strength over the base metal.
These Weld Mold fillers can be used with minimal preheating (often none) as opposed to classic pre-heating or even in-the-furnace welding of castings.  Once you start welding with 700 and 750, successive passes can nearly always be made without re-heating the metal.  I always encase the finished and freshly welded piece in a Kevlar welding blanket to allow very slow cool down without exposure to drafts or breezes.  The iron axle in the slideshow/video took nine hours to cool down after each day I worked on it. 
When you're through watching the video, visit the Weld Mold Company website for details on niche filler materials.  They service the precision tool and die industry, where exotic metals and alloys are often attached and welded to common base materials. 
An option to welding is the Lock-N-Stitch technique, which is similar to what machine shops do with exhaust valve seat cracking and block or head minor cracks.  This is typically a drilling, overlapping screws or plugs and finishing process.  It works well on block castings in non-structurally supporting areas.  If the block crack can affect the structural integrity of the cylinders, I always TIG repair with cast iron filler like 700 and 750!
The 700 and 750 fillers are available for several welding processes, not just TIG.  So if you prefer SMAW (stick), GMAW (MIG) or even oxy-acetylene, you can take that approach.  Again, my preference is TIG (GTAW) process.

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