How To Repair Cracks In Cast Iron

| November/December 1990

662 Lambeth Ct., Sunnyvale, CA 94087

I have noticed comments on welding cracks in cast iron in recent issues of GEM. While I agree that it is possible to weld cast iron, it does require skill with welding equipment and a place to heat and cool the part to be repaired so that the weld holds up. (See 'Cracked Engines,' page 5, August 1990 GEM.) To further discussion on repairing cracks in cast iron, I thought readers might be interested in recommendations on repairing cracks in cast iron engine blocks and heads from the 1928 book The Ford Model A Car: Construction, Operation, Repair by Victor Page. Some of the terms used are quite old. I hope that some readers may be able to identify them and suggest modern equivalents. For example I think shavings from regular brass brazing rod could be used for the spelter. Anyway, here are crack repair methods from the days of Model T's and Model A's.

Repairing A Cracked Water Jacket: The water jacket of the Ford engine cylinder block will sometimes become cracked due to freezing of the cooling water or perhaps as the result of a sand or blow hole which opens up from vibration after the cylinder has been used awhile. At the present time, the usual practice in repairing cylinders is to fill the depression or crack with iron by autogenous welding process, al-though various iron cements may be used to that purpose if the fracture is not serious. A mechanical repair is always possible, i.e. a metal patch can be applied to cover the crack and held in place against a gasket interposed between the plate and the cylinder jacket by small machine screws tapped into the iron.

Mechanical Method: If the crack is of some length it may be repaired by the following method: On the line of the fracture, drill and tap for a 3/8 inch threaded copper rod. The rod is screwed in firmly to a depth about equal to the thickness of the metal in the water jacket. Cut off the copper rod with a hacksaw, allowing it to project about 1/32 inch, then drill succeeding holes, each being drilled partly into the previously inserted copper plug, so that when all the plugs are placed in the cylinder casting, they form a continuous band of copper along the fracture. The copper plugs should be peened down and trimmed off flush. The only possible chance for leakage, after having repaired the crack in this manner, is for the water to follow the joint between the metal of the jacket and the copper plugs, but as the copper rods are threaded into the casting, it is not likely to occur. Should leakage take place, a little extra peening will suffice to prevent it. The copper surface can be cleaned and tinned with solder as an added precaution.

Fusing Spelter in Crack Still another method involves fusing brass filings or granulated brass spelter into the crack. This has the advantage of not requiring the removal of the part to be repaired. Drill and tap a small hole at each end of the crack to prevent further extension of the weakness and screw in an iron stud. Next clean the outside and inside of the fracture very thoroughly, using a scraper and gasoline. File up some soft brass spelter, mix with borax and fill the crack, heaping the filings over it. Then take a powerful blow lamp or torch and direct the flame on the copper. By this method a fair amount of metal may be worked into the opening. After cooling, the studs are cut off flush and the spelter filed smooth. It's said that the repair will endure indefinitely if properly made.

Rust Joint In many cases where the crack is not serious it may be closed by making a rust joint. The first step is to drill a very small hole at each end of the crack to prevent it from spreading and drive in or screw in a metal plug into each hole. The crack is then filled up with a paste made of 66% iron filings or iron dust and 33% sal ammoniac in pulverized form, with just enough water to make the mixture of proper consistency to be pressed into the crack easily. The action of the sal ammoniac is to rapidly oxidize the fine iron filings, producing a rust which joins the various iron particles tougher and effectively seals the opening when it has hardened.


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