What is core shift in a engine block?

Easiest way for me to describe...
Is the cam bore somewhat centered in the cam bearing bosses cast into the block, both front and rear? That, to me, indicates the severity of core shift.

I understand that it's caused by shifts in the sand casting molds which causes cylinder barrels, camshaft bosses, etc. to be off-centered from perfect. The cam boss is used as a reference since it's visible and easy to judge shift or even measure it with a caliper. Core shift causes cylinder walls to be very thin on one side as compared to the other. As long as your thrust surface is the thickest, you're fine. The only reliable way to test is with a good sonic test. Engine gurus, is this close to right?

... is this close to right?
You got it! :thumbsup:
Cam boss casting area is the best place to guage core shift because it is the center point of the mold. If it's shifted out there, it's worse yet higher up the block.
Spent 5+ years doing "time" at Chevy Tonawanda Engine/Foundry plant in the mid '70s.

Fwiw, HPBooks old book, "How to Hotrod Small-Block Chevys" has a pic in it on page 4 that show's all of the new cores they used back in '55 to cast a SB.

I figure the BB cores are basically the same if you want to look deeper into this subject?

I'm fascinated by this stuff b/c I have done a lot of refractory furnace repair in foundries way back when I worked for APGreen Refractories Co. (Both hot gunning and cold gunning!)..

pdq67

I guess that can cause a problem when boring to the max of a block.Do most machine shops check for this before boring the cyl?