Cracked Block Repair

[George Willer]

This is what I have done in the past and plan to do again soon to another engine. (On a recent eBay prize). When I get a round tuit I plan to take photos, but for now I'll try to do it with words, as best I can remember from a dozen years ago.

The load that breaks the ears is mostly tensile. Cast iron isn't very strong in tension, and in spite of what many think welded cast iron near a repair is even weaker, although the weld itself may be very strong. For that reason I use bolts.

The 3 lowest front cover bolts (3/8") are removed and the holes drilled out to 7/16" clearance as deep as the crack (and no deeper!) and then the hole is continued as deep as absolutely possible for 7/16-14 tap size without breaking through and tapped with a bottoming tap. 2 more new holes are then drilled between the originals and treated the same way so there are 5 bolts to carry the load.

It's very important to have as many threads as possible, so maybe all but the top one which would break out in the oil pressure relief could be through holes. (I used all closed holes before, but through if possible would allow more threads) Each grade 8 bolt should be bottomed and the amount remaining under the head measured to determine how much to shorten, and each bolt should be marked so it goes in the right hole.

I don't know for sure this repair is as strong as original, but it must be close. Only those with sharp eyes will see the larger bolt heads and the one extra that is visible, so this could even be done to a damaged show tractor.


For more information on this subject or further questions, please read the original Cracked Block Repair thread, and post questions. Thanks.