Another "Anyone see this before" post - Cylinder size numbering


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By MattsY - 5 Months Ago
Hello all! I haven't been here long and I haven't posted much. But I've been trolling quite a bit and learning as much as I can. I posted before about the industrial engine tag under the fresh red paint on the motor in the '54 my son bought and I posted the spun 4 and 8 rod bearings in that motor. I just loaded the block, a 312 crank with the ECZ rods and a pair of ECZ-G's into the back if my truck for a trip to the machine shop and I couldn't help but snap a pic of some writing on the deck of the block. I obviously noticed it upon tear down, but not curiosity has gotten the better of me a d I have to ask.....Has anyone seen this before? As always, thanks for your time!http://forums.y-
blocksforever.com/uploads/images/76ec1b6d-3749-4c19-b63d-6c81.jpg">
Sorry the pics are upside down. I don't know why they did that.
By MattsY - 5 Months Ago


By Joe-JDC - 5 Months Ago
I have seen similar writing on blocks that were service blocks and the numbers were for oversize when measured.  Required fitting pistons and rings to match, or overbore.  It would be interesting to measure the bores before any machine work to see what the size actually is.   8 being +.008(3.808")?  5 being +.005(3.805")?  Joe-JDC
By MattsY - 5 Months Ago
Joe-JDC (4/8/2019)
I have seen similar writing on blocks that were service blocks and the numbers were for oversize when measured.  Required fitting pistons and rings to match, or overbore.  It would be interesting to measure the bores before any machine work to see what the size actually is.   8 being +.008(3.808")?  5 being +.005(3.805")?  Joe-JDC



Joe, thank you for your reply! It's funny you say "it would be interesting to see" the bore size.....I did measure. Actually, I only measured 1 and started scratching my head as I came up with 3.755" (it's a 292 block) and the pistons were at around 3.751. I found d several "other" issues as I was tearing it down as well. Out of curiosity, were industrial engines any different from the passenger car counterparts?
By Ted - 5 Months Ago
Those hand scribed numbers were put on the block after the honing operation.  On the FE engines, you’ll see those numbers in the lifter valley area.  Those were there to aid the engine assembler to match the varying cylinder bores to the correct piston to help keep piston/wall clearances more consistent.  No block left the machining operation with the exact same finished bore between the cylinders.  This allowed pistons with slightly larger diameters to be fitted to the bores that were slightly larger.  Likewise with the smaller bores where the smaller diameter pistons were being used.  You’re dealing with tenths of thousands of an inch here so the differences are quite small.
By Joe-JDC - 5 Months Ago
Several years ago I bought a pallet of 5.0 HO blocks when Ford was selling off their left over stock, and the blocks had those large numbers on every block and each bore.  When we used a bore gage to measure them, it was in thousandths.  Had to buy oversize pistons for every block, and Ford did offer 4.003" pistons for a while as an option.  Joe-JDC
By MattsY - 5 Months Ago
Interesting stuff! Thank you all! This car is really turning into an adventure as well as an education.
By Ted - 5 Months Ago
Here’s some information on those block numbers that was found in one of my Service Specifications Handbooks.  For the 292’s, those numbers represent eight grades of bore sizes and the appropriate sized pistons were put in the bores based on the ‘grade’.  These numbers are only pertinent at the time of factory engine assembly and anything done at the dealership simply had a ‘red’ and ‘blue’ piston in which to accommodate the bore size.  Here is how the ‘grades’ relate to bore sizes for the 292 engines.
1 –  3.7500-3.7503”
2 –  3.7503-3.7506”
3 –  3.7506-3.7509”
4 -  3.7509-3.7512”
5 -  3.7512-3.7515”
6 -  3.7515-3.7518”
7 -  3.7518-3.7521”
8 -  3.7521-3.7524”