Patching a Leaky Block?

The 39 B I purchased this spring had a couple of "wet trails" weeping down the block, from behind the carb.  I incorrectly assumed the block petcock was leaky or loose.  Now after removing the carb and closely inspecting, I can see the leaks are coming from very small cracks in the casting line that runs right above/through the threaded hole for the petcock.  What would you guys suggest?  It looks like it's been doing it for a long time (from the stain streaks on the block) and I don't notice significant loss of fluid.  I was wondering about draining the coolant, drying the block real good, and applying a liberal amount of JB Weld.  Any advice would be really appreciated.

use a nickle wellding rod  drill the ends of the crack. or  drill and tap into the crack with smal bolts notched to break off then V it out and fill with JB weld. Make sue everything is clean

Drain the block,  and pull the sleeves. You now have access to the back side of the casting, around the petcock hole. Clean that area super well, glass beading would work great, if you can get the nozzle in there. Spray it all down good with brake cleaner and let it dry out.

Edited by GlenninPA - 07 Dec 2010 at 11:35am

The best epoxy for this type of repair is Belzona 1111 Super Metal. 
It is even specified by Caterpillar.  There are several major engine rebuild shops using Belzona for this type and many other repairs. 
Three basic things to remember when doing a repair with any epoxy.
1. The surface MUST BE CLEAN.  Since steel is basically porous, the surface should have any visible contaminants removed. Use a low temperature flame to sweat the en-grained oils to the surface and wipe them away with a non petroleum based solvent (acetone, MEK).
2. The surface MUST BE FIRM.  The repair will not be successful if the part moves.  It should be mechanically locked down (metal stitching, drill tap bolt method, strategic welding).
3. The surface MUST BE ROUGH.  Most epoxies have good tensile strength but they need to be able to tooth into the surface.  Blast cleaning with a coarse angular abrasive (Black Beauty) will produce an ideal profile for the epoxy to lock into.  Other methods are also acceptable such as grinding or scoring.  Anything to roughen the surface and create more surface area than a smooth surface.
Follow the manufactures instructions.  Do not try to adjust the mixing ratio. 

If you are going to go to all the trouble of getting to the insdie of the block.  All you need to do is clean it good and paint it.  Cast is pourous and natually leaks/seeps.  Painting it seals it so it does not.  Probably just wore the original paint off and that is where your seeping is coming from.  Don't attemp the major surgery if all you need is a couple stiches. 

If its just weeping, you can try the silver solder radiator stop leak. Another alternative is the ceramic leak sealer that requires you to thoroghly flush the coolant sytstem to remove all the antifreeze, fill with fresh water, dump the sealer in, run the engine for an hour or so to get it hot, drain the water, and let set for 12-24 hours, then refill with antifreeze solution. Used the stuff to cure a leak in the rear of a 262D between the head and block. Worked great (and still is) and a whole lot cheaper than pulling the head, etc.

Greg - Can you suppluy brand bames for the silver solder stop leak and ceramic product you have used?

Thanks for all the advice guys.  I think I know the approach to take now...just need to decide which epoxy product to use.  When drilling and tapping for the small screws, do you do that prior to grinding out a "V" in the crack, or after grinding it?