[BRENT in 10-uh-C]

This thread is going in a direction of "I have done this and gotten away with it..." which is NOT what I intended this thread to be. To me, this is much akin to saying I have driven 100mph several times without receiving a ticket, therefore it is ok to do this regularly. Again, no one in their right mind would stake all of their earthly possessions guaranteeing they could do it again and not be cited for speeding.

So let me reel this back in. Kurt pretty much nailed it when he asked about the factory wall thickness and piston sizes. According to my prints, the wall thickness on a std bore was 0.250" thick from the factory. As I was looking at my 10/01/1929 A-6015-A print, it mentions "Diameters for Reconditioned Engines ..." and goes on to list 1st Oversize of 3.876" (--0.001 oversize), 2nd Oversize 3.880" (--0.005" oversize), 3rd Oversize 3.905 (--0.030" oversize), 4th Oversize 3.915" (--0.040" oversize), and 5th Oversize 3.935" (--0.060" oversize). Now this information was list in October of 1929, so this information was not listed because the Agencies had engine already on their 5th rebuild, -but was listed to provide guidance on the maximum overbore the engineers deemed prudent. Therefore, the minimum cylinder wall thickness they allowed was 0.220".

As mentioned above, many engines have seen very sloppy machine work causing cylinder bores to be machined off-center, and even slanted from perpendicular with the crankshaft centerline. As many would agree, this potentially causes the cylinder wall thickness to be less, -as does rust pitting or core shift during casting. Why I am asking this is I have recently had some discussions with a few hobbyists (-and one engine rebuilder) who are having overheating issues that potentially are being caused by cylinder wall hot spots. I have a sonic tester that I try to scan the bores, and because my tester defaults to metric, I just use 5mm on the tester as my minimum thickness baseline. That basically meant I felt could safely bore to 3.975" using 0.100" over pistons with a fair amount of certainty that I was not going to have a likelihood of cooling issues. With the manner in which many Model-As are being driven (-higher speeds, lugging, greater loads due to overdrives, etc.) in today's environments, the importance of not having cooling issues are greater than ever.

Therefore with the above said, I need to establish what that threshold of wall thickness needs to be for me to properly warranty an engine. Granted, no one wants to spend $500.00 to sleeve a block back to 3.875, ...but they also complain when their block was bored too thin causing heating issues.

So, what should that number be that if any cylinder wall in their block is beyond a certain minimum thickness, then they understand there is no warranty? Since Ford engineers stated 0.060" was to be the maximum overbore, is the minimum thickness number 0.220"??