How to repair a cracked block in a marine engine

Written by april kohl
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How to repair a cracked block in a marine engine
When repaired correctly, a marine engine will last a long time. (Jupiterimages/ Images)

A cracked block in a marine engine does not have to signal the end of the engine's life. A poorly winterised engine block can experience small cracks that can be fixed with the right tools and the metal stitching method, which is far more suitable to the task of repairing marine engines than traditional welding. These small repairs will significantly extend the lifespan of the marine engine, preventing expensive replacement costs and letting you keep your boat on the water longer.

Skill level:

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Things you need

  • Drilling jig
  • Metal stitching kit
  • Hammer

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  1. 1

    Drill holes in the engine casing, in a line along the crack. The holes should be drilled on both sides of the crack using a drilling jig with a centre at 1/8 inches to achieve the correct spacing. Once the holes are drilled, covert the holes into slots by drilling a series of smaller holes between the larger ones on either side of the crack.

  2. 2

    Purchase a metal stitching kit from your local marine supplies shop or engine supplies store. The locks should be made from steel with a high nickel content so it is strong enough to withstand the forces the metal will be placed under. Fit the locks from the metal stitching kit into the slots you drilled in the engine casing and tap them firmly into place with the hammer.

  3. 3

    Drill holes between each of the locks, along the length of the crack. Slide the taps from the metal stitching kit into the holes and tap them into place with the hammer. Insert the screws from the metal stitching kit into the taps, following the instructions with the kit. Grind the surface to level off the repair and make it flush with the rest of the engine casing.

Tips and warnings

  • If the damage in one area of the casing is extensive, it is sometimes possible to repair the section by cutting out the damaged area. This will create a metal patch "insert" that will fit into the casing using the metal stitching method. Like the locks from metal stitching kits, the insert must be of a sufficiently high quality metal to withstand the pressures that will be placed on it, however.
  • Under no circumstances should a cracked block in a marine engine be welded. Welding aggravates damage in a cracked engine block and weakens the casing, causing further damage to appear at a later date. It is possible to use welding to repair holes in an engine, but cracks will spread when welded.

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