Repair
a cracked engine block without welding.
From
the beginning of the winter, at field areas on extreme cold climatic condition,
some block of the engine are cracked by frozen of water inside of the block due
to our carelessness. Cracked
cast iron engine block welding is
difficult or impossible in many cases, especially when considering the damage
wrought by rapid heat expansion and cooling. Cold metal-stitching isn't
something the average mechanic can or will do at home — it's something of an
art that requires numerous specialized tools and skills — but knowing what's
involved may at least help you sleep better when you get the bill back from a
machine shop.
Procedures:-
1 Identify the crack
with your three-part penetrating dye system. First, spray or paint your penetrating
dye over the suspected crack and the surrounding area, then wait 5 minutes.
Spray the dye-cleaner on a lint-free cloth and clean all of the dye off of the
surface of the block. Once you have all visible traces of dye off, spray a
light or "dry" coat of developer over the area, then use compressed
air to accelerate the drying. Wait at least 1 minute; the crack will be clearly
visible in bright purple, red or blue.
2 Identify the three
types of stitching pins in your kit. The standard L-series pin is a straight-threaded
pin that looks like a machine screw with the shaft slightly tapered outward
toward the head. Near the head, you'll see a groove that allows the screw-head
to break off. This type of pin exerts a spreading pressure on the crack to seal
it. The second type is longer, has a flat tip, uses spiral-hook threads and
uses a non-tapered head; it exerts a radial clamping force and is used for
structural integrity and sealing.
3 Drill a hole through
the block (size recommended by the pin manufacturer) just before the crack
starts. Place the drill jig so that its locating pin sits in the first hole,
then drill down through the jig guide's two holes to create a line of three
holes. Move the jig so that the locating pin sits in the last hole and repeat. Continue
until you have a line of holes running through the entire length of the crack.
4 Spot face or
"countersink" the holes using the spotfacer. This is the most
important step in the whole process. Set the spotfacer's depth guide so that
1/8- to 3/16-inch of material is left in the casting for the pin threads to
grab onto. Countersinking too deep will not leave enough material for the pin
to grab, and countersinking too shallow will fail to seal the block. Once you've
set the depth guide, lubricate the pin hole with plenty of tapping fluid, and
use the spot facer to create the holes into which the pin "shoulders"
will fit.
5 Tap the holes using
the kit-supplied power-tapper or your own tap sized to fit the manufacturer's
recommendations. Keep the tap lubricated with either tapping fluid or tapping
wax. Remember to use a back-and-forth tapping technique; turn the tap 1/4 turn,
back it off to remove the material, turn it 1/2 turn, back it off 1/2 turn to
remove the material, turn a full turn (cutting another 1/2-turn's worth of
thread), back it off 1/2 turn and repeat until the hole is fully tapped.
6 Drive the L-series
pins into the holes, continuing to turn them until the bolt head snaps off. If
you're sealing a portion of the block that intersects a water jacket, then use
the manufacturer-recommended thread sealant on the pin threads before you
install them. Keep going until you've installed pins in all of the holes. Once
you've got pins installed in all of the holes, you've got the first row
completed.
7 Drill a single hole
just to the right of the left-most pin so that the hole starts just at the edge
of that pin's shoulder. Use the drill jig to drill another series of holes; all
should land on the right-hand edge of another pin's shoulder. Spot face and tap
those holes. The spot facer's cutting head will actually cut into the adjacent
pin's shoulder. Install the pins with thread sealant and continue until you've
filled all the second-series holes.
8 Drill, spot face, tap
and pin a third series of holes in the remaining gaps between the installed
pins. At this point, you'll have removed all of the original cast iron and
you'll be spot facing into the pins on both the left and right sides. Once
you've finished this third series of pins, you'll have created a fully
contiguous "weld" running the length of the crack where the sides and
heads
of each pin overlap the next.
9 Grind the pin
shoulders almost level with the block (leaving a small ridge for needle
scaling) and examine the stitch for gaps. You can do this either visually or by
applying more penetrating dye. If you find any gaps, drill, spot face, tap and
fill them with another pin. Don't be afraid to use the pins as
"fillers" between other pins; the pin material is stronger than your
original black, and it can take some drilling into.
10 Pressure-test the block with compressed
air and soapy water, watching for bubbles in the crack. If you see any, then —
you guessed it — install a pin in the hole. Once the block is leak-free, use a
pneumatic or electric needle scaler (which looks like a bunch of metal
ball-point pens all bundled together) to flatten the pin heads, sealing them
completely and leaving a factory-looking finish.
11 Paint the repair with a sealing epoxy (JB
Weld also works well for this task), sand it flat and then paint the block with
a high-temp engine epoxy or enamel. Your new stitch-weld will have similar
expansion characteristics to the cast iron and should ultimately outlast the
cast engine block around it.
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