The absolute 'MINIMUM' cylinder wall thickness....

[BRENT in 10-uh-C]

Originally Posted by Bob Bidonde

Hi Brent! The sand casting process is not a precision one, and it was my experience that my sand cast designs were at the mercy of the pattern maker's best effort and the actual casting process. Sample castings were destructively measured and dimensions feed back to the engineer for structural and functional analysis. If found acceptable, the engineering drawing would be revised to reflect the actual dimensions. Did Ford do this???

I recommend that you survey some Model "A"engines that have been cutaway, and check their cylinders for wall thickness and bore size to analize their original wall thicknesses. The limiting walls have to be those between Cylinders 1&2 and Cylinders 3&4.

I am assuming that Ford engineers did a structural stress analysis, a thermal stress analysis and a thermodynamic heat transfer analysis to determine their 0.060" oversize piston is serviceable. So as a business man, I would not recommend boring cylinders more than 0.060" as Ford limited by service piston size.

Bob, I agree with you however the print shows the finished thickness size to be 0.250". It does not give a + or - tolerance with that number. Based on the sheer quantity of blocks that were cast, and based on the methods Ford used, my guess their QC was very close on these measurements.

I do have an ultrasonic tester that we use to verify wall thickness, and the tester is calibrated to be within 0.001±" of what the display screen reads.

As far as the "limiting factor between 1&2 and 3&4, the bores are siamesed in most of those areas, so generally speaking I don't think that area is affected much except the upper 2" where the temps are the hottest.

I think your logic about 0.060 makes sense. There is less than 3% difference in cubic inch displacement between a standard bore vs an 0.060" overbore, so the benefit there is negligible ...however sleeving back to 3.875" and the rigidity and/or heat transfer you would gain by properly installing sleeves would likely be huge with regard to cooling.

Originally Posted by Jim Brierley

Just how many people do you think have ever measured that thickness? I think not many, less than 1%. So how do you expect to get any exact answers? People above have said that a 4" bore (.125") will still allow the A engine to run cool, what more do you expect? I have raced my B engine on the Bonneville salt flats with a 4" bore with no heating problems. In the old days guys raced them with at 4.060". This required off-setting the bores to gain head gasket sealing between 1&2 and 3&4 cylinders, many did this. Racing puts a lot more heat into the block than driving to the local market. Get real!

Hey Jim, Happy belated Birthday last week. To your point, I don't think many rebuilders have ever checked them. Many rebuilders never Magnaflux or pressure test them either simply because it is a time consuming process that most customers don't want to pay for ...unless an issue was found. I think the level of professionalism and the expectations that should be coming from a professional rebuilder in these times are much different than a decade or so ago.

As for Bonneville and a 0.125 over engine, I agree that it has been done successfully however I can refer you to an engine rebuilder whose customer has a 0.060 block that appears to have a couple areas thin enough to produce 'hot spots' for his customer. The amount of lost revenue and time this issue has caused this rebuilder dealing with this troubling.