Features

How to repair a cracked engine block - pictures

by: Auto Express team

27 Sep 2017

Go to: How to repair a cracked engine block

The problem: The crack coincided with the coolant passage, which protrudes at mid height along the left side of the engine block (note leakage stains).
The visible part of the crack runs horizontally and around the drain tap, between the alternator and the starter motor.
Adding industrial quality sealant to the cooling system might have effected a temporary repair, but did not completely seal the crack.s
Spare block (from a SIII Lightweight petrol) would have made a good replacement after re-boring, but would’ve involved swapping engine internals over.
The position of the water passage which cracked on my engine is marked with the arrows on the inside of this spare engine block.
Stitiching the crack: In preparation, the exhaust manifold, alternator, starter and dipstick tube were removed to improve access. Exhaust ports plugged to deter grit.
After cleaning the surface along the cracked area, white background paint is applied, the magnet fixed, and particles are washed over.
The magnet causes the magnetic particles to align along the crack (arrowed) revealing the exact route and the full extent of the crack.
Crack follows around casting bosses. Neil centre-punches along the crack to provide drilling positions for studded plugs to be fitted later.
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.
The result is an accurately spaced series of holes drilled across the crack in numerous positions. This forms the basis of the main stitching.
Between each row of drillings, the crack itself has been drilled and a self-tapping screwed plug inserted with sealant, before cutting off flush.
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.
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.
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.
Each key, coated with a sealing compound, is initially tapped into the serrated slots using the light hammer, until all are in position.
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.
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.
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.
Screwed plugs are fitted with sealant into each new hole, connecting with each other to replace the crack with a line of sealed inserts.
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.
Finally, excess sealant is removed and the complete area of the repair is ground smooth, removing all traces of the plug and key inserts.
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.
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.
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.

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