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Re: has anyone successfully repaired a cracked block?

From: Hank Dozier
Date: March 27, 2002


Ted...Depends on where they are and how far they extend. If they are external (nothing into the inner oil side of the crankcase), and if they are localized around a freeze plug, then you can repair and have 2 options. Option 1 (This should be done if further machining of the block is necessary in any event - eg: boring, sleeving, align-hone, etc). For this option find the maximum extent of the crack(s). At these points CAREFULLY drill a small hole to terminate and stress relieve the crack. Then take a die grinder and grind a groove through the center of the crack, but not more than 3/4 of the thickness of the local casting thickness. This should go the length of the crack. The block should then be pre-heated SLOWLY up to about 700-800 F. With the block at that temperature, using a gas torch, heat the area around the crack further until you see the metal just start to turn. Do NOT get it so hot it turns red. Dull color at most. Now with someone keeping it at this temperature, using a high nickel rod, electric weld the crack, from hole to hole. Afterwards, keep the torch on the metal for about 2-3 minutes, and then put the block back into the oven for about an hour. Turn the oven down in stages of 200 degrees and let the block sit an normalize for about 3 hours per point before reducing further the temperature. When you reach 200, turn off the oven, and remove the block and let air cool. The above will repair the crack, and will minimize block distortion. Option 2 (all machining done): With is option, although not a strong, it should repair small non-structural cracks. Follow procedure and drill holes and groove crack as above. Now, in the holes you drilled, peen in a repair dowel (try a tractor dealer to get these cast iron pins) of the correct size for the hole. Using block repair epoxy (also available at tractor supply outlets), fill the groove with this compound. Make sure your block is at room (above 70 F) temperature. I havel also "mounded it" slightly and extended the surface area for grip to twice the groove width. Let harden for a couple of days. Hope one of these methods work. If yor block is pre-1962, it is most likely high nickel-iron material, which welds much better than the low-nickel that was used untill about 1966. At that time the infamous "grey" iron that used carbon to replace nickel became in use, and those blocks require a lot of "finesse" to weld.


Last changed: July 19, 2018