6D102 - 6 Diesel Used Engine Blocks For PC200 - 6 PC200 - 7 3928797

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A cracked cylinder head or engine block may or may not be bad news

A cracked cylinder head or engine block may or may not be bad news depending on the size and location of the crack(s), the value of the casting and what it will take to fix the crack(s) versus what it would cost you to replace the casting. A relatively common casting that is badly cracked is probably not worth the time and effort to repair it, assuming you can find another clean casting at a reasonable price.

On the other hand, if you’ve discovered cracks in a late model cylinder head or block that’s relatively pricey or hard to find, it may be more economical to fix the casting using the proper crack repair techniques. To spoil the conclusion of this article, it comes down to weighing the cost of repairing a cracked casting against the cost to replace it.

Of course, there’s more to the story than just the end. Anytime you are rebuilding a used, high mileage engine, the head and block should always be carefully inspected for cracks. Magnetic particle inspection techniques will reveal most surface cracks down to a depth of about a quarter of an inch on cast iron blocks and heads. But some areas can be difficult to inspect with magnetic particle detection alone, so pressure testing is recommended to check for “hidden” cracks in intake and exhaust ports and water jackets.

With aluminum castings, cracks and porosity leaks are usually found by using penetrating dyes and/or pressure testing. Pressure testing at 10 to 40 PSI will usually uncover any porosity leaks or cracks that are worth worrying about. There’s no need to use a higher pressure because most leaks that occur at normal operating temperatures and pressures will show up with 10 to 40 PSI of air pressure. Submerging a casting in hot water while pressure testing it is another technique that can uncover cracks and porosity leaks that might otherwise be overlooked at room temperature.