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Core Shift And How To Spot It

Posted January 25 2009 09:26 AM by SMART67 
Filed under: Miscellaneous

Does core shift make your castings automatic discards?


Do you see the oil galley passage dead center on this small-block Ford main bearing?  This is a perfect core.
These lifter bores are dead center in the casting bosses indicating no core shift.
Core shift is impossible to see with cylinder bores. However, if you sonic-check each bore, you can determine cylinder wall thickness.
Core shift, which is not uncommon, can be spotted at main bearing saddles just by looking at oil galley passages as they relate to bearings.
Some core shift is evident here at the oil pump boss on a 289 block.
Marvin McAfee of MCE Engines in Los Angeles is the first engine builder to ever bring core shift to our attention.  Marvin stresses sonic-checking cylinder wall thickness, especially if core shift is evident elsewhere.

What is core shift and what does it mean for your engine build?  Core shift is quite common and easy to spot when you're rebuilding an engine.  And depending on how bad it is, it can adversely affect your engine build.

Core shift is what happens what an engine block, cylinder head, manifold or other type of sand casting shifts in the mold when molten iron or aluminum is poured into the mold.  When core shift happens, it can throw factory machine tooling off, mislocating oil galleys, cooling passages, lifter bores, and even cylinder bores to where wall thickness gets dangerously thin in places.  This isn't as critical with a stock rebuild, but very important if you're going racing.

When you spot mislocated lifter bores and oil galleys, it isn't always core shift.  Sometimes it was miscalibrated tooling as well, but a rare occurance.  Most of the time, it's core shift.  Keep core shift in mind and thoroughly inspect before having expensive machine work performed.

 

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