How to repair a cracked engine block - pictures

<span>The visible part of the crack runs horizontally and around the drain tap, between the alternator and the starter motor.</span>

<span>Adding industrial quality sealant to the cooling system might have effected a temporary repair, but did not completely seal the crack.s</span>

<span style="font-size: 0.8125em;">Spare block (from a SIII Lightweight petrol) would have made a good replacement after re-boring, but would’ve involved swapping engine internals over.</span>

<span>The position of the water passage which cracked on my engine is marked with the arrows on the inside of this spare engine block.</span>

<span>Stitiching the crack: In preparation, the exhaust manifold, alternator, starter and dipstick tube were removed to improve access. Exhaust ports plugged to deter grit.</span>

<span>After cleaning the surface along the cracked area, white background paint is applied, the magnet fixed, and particles are washed over.</span>

<span>The magnet causes the magnetic particles to align along the crack (arrowed) revealing the exact route and the full extent of the crack.</span>

<span>Crack follows around casting bosses. Neil centre-punches along the crack to provide drilling positions for studded plugs to be fitted later.</span>

<span>Several punch marks are drilled out to locate this jig which allows Neil to drill a precise series of holes across the crack, at 90 degrees to it.</span>

<span>The result is an accurately spaced series of holes drilled across the crack in numerous positions. This forms the basis of the main stitching.</span>

<span>Between each row of drillings, the crack itself has been drilled and a self-tapping screwed plug inserted with sealant, before cutting off flush.</span>

<span>Each series of vertical drillings is then joined up using a pneumatic chisel to cut through the metal between each hole, joining the holes together.</span>

<span>The chisel produces a cut narrower than the diameter of the holes it is joining. Thus, it turns each series of holes into a serrated slot.</span>

<span>Metal keys are fitted in each slot to hold the crack together. They have the same expansion rate as the block material, so will stay tight when hot.</span>

<span>Each key, coated with a sealing compound, is initially tapped into the serrated slots using the light hammer, until all are in position.</span>

<span>The keys are then driven fully home and expanded into their slots using a pneumatic impact tool which also peens the tops over almost flush with the surface.</span>

<span>The result isn’t pretty, at least at this stage. But it will look great eventually. Meanwhile, there’s more drilling, tapping and plugging to be done.</span>

<span>The remaining centre-punch marks along the line of the crack are now drilled out for more plugs. Each one is between an earlier plug and a key.</span>

<span>Screwed plugs are fitted with sealant into each new hole, connecting with each other to replace the crack with a line of sealed inserts.</span>

<span>The protruding ends of each of the screwed plugs are removed by the pneumatic chisel, cutting them slightly proud of the surface of the block.</span>

<span>Finally, excess sealant is removed and the complete area of the repair is ground smooth, removing all traces of the plug and key inserts.</span>

<span>Testing the repair: A further magnetic particle test is carried out on the newly prepared surface to confirm that all traces of the crack have been removed.</span>

<span>Finally, coolant connections are sealed and a 10 psi air pressure test applied, while checking for leaks with soap solution. There are no tell-tale bubbles – it’s tight.</span>

<span>After re-painting, there is no evidence of the repair. The real test of running the engine will have to wait until the bulkhead is on and systems connected.</span>