What is the maxium safe bore on these blocks ?

Sample size of one:
The race I built my 430 for allows .070", however, I sonic checked the '59 block I used and felt .060" was max.
It was close enough we offset bored the passenger bank .010" to compensate for core shift.
I have the wall thickness recorded but not with me at this time.

Brian Perrenot is running 100 thou over pistons in the Gizzlehopper, and told me his dad used to use 150 thou over pistons on one engine. The issue is not wall thickness, but integrity of the cast. These are old sand cast blocks, and on a good one, 150 wouldn't be too much, on others you could go 60 thou and run into a sand pocket. Sonic testing the block would tell you for the most part, but not always.

Chris Craft crazy wrote:.......... you could go 60 thou and run into a sand pocket. Sonic testing the block would tell you for the most part, but not always.

Yep, sonic testing is a good idea If you plan to get the block corrected for core shift. Then after the block and bore true process, go for one more sonic test to determine what max. size over you might want to go for.
In the end after spending all that money and time a sand pocket is what can bring all that effort down occasionally. I've been there once. We ended up pressing a cylinder sleeve into that cylinder. With a competent machinist things work out fine in the end.
Good luck.

Chris Craft crazy wrote:Brian Perrenot is running 100 thou over pistons in the Gizzlehopper, and told me his dad used to use 150 thou over pistons on one engine. The issue is not wall thickness, but integrity of the cast. These are old sand cast blocks, and on a good one, 150 wouldn't be too much, on others you could go 60 thou and run into a sand pocket. Sonic testing the block would tell you for the most part, but not always.

The late Ted Cyr told me he kept the cylinders at standard to .030" over due to the thin walls.

Also keep in mind that thin cylinder walls and possibly more than average blow by due to cylinder wall flex is definitely not your friend.

Theo wrote:Also keep in mind that thin cylinder walls and possibly more than average blow by due to cylinder wall flex is definitely not your friend.

Very true, wall thickness is always an issue.

Core shift can vary from minor to exorbitant. Take a look at this FE block that I once built. The pic shows one of the bores after it was machined and bored w. my BHJ "block true" and "bore true" tools. All bores were shifted into various different directions.
If my memory serves me right this was done at 0.030" over. At this stage we took figures and determined that the bores would clear fine at 0.040" final bore and hone.
Only at this "pre" final bore and hone stage you should order the pistons according to the targeted final size. After the pistons arrived they were marked by numbers from one to eight so every individual bore could be honed according to each pistons size.

The minimum wall thickness that is listed in the Lincoln maintenance manual I have is .170 but this was a Lima sand cast, it's as heavy as can be. I bored .045 on my current build, and not an issue.

Just in case I wasn't clear enough. The above photo of the bore is one of the bores that have been bore true bored to 0.030" over. The dark area is where the cutting tool didn't touch the wall due to core shift. To get the bore completely bored round, we determined that it would take an other step, up to 0.040".