The Ford Barn

slatgrille · 06-08-2024, 06:03 PM

Okay Model A'ers, I have to pick your brains about what can be done about the following.

In my other topic I asked about the odd sized rod nuts which morphed into discussing valves and babbitt. Now my topic is pistons/rings/cylinder sizes. In short, this engine ran fine except for a nagging knock. I went ahead and removed the pistons and valves. I'm all set regarding doing the valves, but today I measured the pistons and cylinder bores. All pistons measure 3.85 and all cylinders measure 3.89. Measuring end gaps of each ring in the cylinders results in excess of .025~.030. This engine had good compression and didn't burn oil. According to Les Andrew's 'Red' book, the pistons should measure 3.8745 and the bores 3.875.

So...what to do. Is the .040 difference I have (actually .020 because of circumference) small enough where I can get away with putting oversize rings in and using my existing pistons? If so, would .010 oversize rings work, or will the end gaps still be too wide? I want to be sure I don't go too big or those gaps will be too small and bind the engine up!

Am I being too worried , or should I just replace the standard rings and put it back together...there are no markings anywhere to indicate the engine has been bored. Each piston is also faintly marked with a Ford script and arrow pointing to the front position orientation when assembled. Those are the only markings.

Experience? Suggestions? Comments? Thanks everyone.

Craig

06-08-2024, 06:03 PM	#1
slatgrille Senior Member Join Date: Feb 2021 Location: Limerick, ME Posts: 172	Next step?.... Okay Model A'ers, I have to pick your brains about what can be done about the following. In my other topic I asked about the odd sized rod nuts which morphed into discussing valves and babbitt. Now my topic is pistons/rings/cylinder sizes. In short, this engine ran fine except for a nagging knock. I went ahead and removed the pistons and valves. I'm all set regarding doing the valves, but today I measured the pistons and cylinder bores. All pistons measure 3.85 and all cylinders measure 3.89. Measuring end gaps of each ring in the cylinders results in excess of .025~.030. This engine had good compression and didn't burn oil. According to Les Andrew's 'Red' book, the pistons should measure 3.8745 and the bores 3.875. So...what to do. Is the .040 difference I have (actually .020 because of circumference) small enough where I can get away with putting oversize rings in and using my existing pistons? If so, would .010 oversize rings work, or will the end gaps still be too wide? I want to be sure I don't go too big or those gaps will be too small and bind the engine up! Am I being too worried , or should I just replace the standard rings and put it back together...there are no markings anywhere to indicate the engine has been bored. Each piston is also faintly marked with a Ford script and arrow pointing to the front position orientation when assembled. Those are the only markings. Experience? Suggestions? Comments? Thanks everyone. Craig