How To Repair Cracks In Cast Iron

By Staff

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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