Max bore on 272 Dearborn block ?

Sonic Test. Sonic Test. Sonic Test. That has saved a lot of blocks that would have been a problem if just arbitrarily boring without sonic testing. This goes for all makes of engines, not just the Ford Y.

As a general rule, all FYB (Ford Y-Block) blocks are safe boring up to a 0.060” oversize bore for non-performance applications. While there are a large number of 272 blocks that have been successfully bored 0.125” over to make a standard 292 bore size, sonic checking those that have survived after running for a period of time found the cylinder walls thin enough that another 0.030” overbore was questionable. What no one talks about are the ones that failed and there were several.

With all that being said, sonic testing will help to determine which blocks can be taken out to the max amounts. Core shift is a major issue and that becomes evident when sonic checking the cylinders. When core shift is found, it’s possible to offset bore the cylinders so as to equalize the cylinder wall thickness rather than have it dangerously thin just on one side. I have done a number of 292 blocks 0.110” over for high horsepower applications but sonic testing was the only way this could be done and still feel comfortable with the engine being trouble free for long periods of time.

There have been some very thick wall blocks made for the 272 engines early on and those can be bored oversize to the extreme. I found one of those by way of sonic testing and that particular block was a 1954 casting; it was successfully bored 0.375” over and made a nice 4.000” bore engine. That engine was done roughly 20 years ago and is still running today in a ’55 Ford in a non-performance application with the original crankshaft and EBU rods.

Here’s the link to an older thread discussing boring 272’s out to the 292 cylinder wall size.
272 bored to 292

Lorena, Texas (South of Waco)

Max bore on 272 Dearborn block ?

Max bore on 272 Dearborn block ?

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