The cylinder case has eight machined cylinder bores to support the piston/connecting rod assemblies (see Figure 2-12). The bores have different diameter sizes, with cylinders #7 and #8 slightly larger than cylinders #1 to #6. The difference in bore size allows for more piston expansion in the rear two cylinders.
During engine manufacture, one of two piston sizes (labeled J and K) is used at each of the eight cylinders and is based on cylinder bore size and recommended clearance. Each piston has a size identification mark on its face and piston pin boss surfaces.
The cylinder case pan rail has a piston size identification marking for each bore (see Figure 2-13). These are matched with the piston sizes during the assembly process.
Piston-to-bore clearance specifications used in manufacturing are as follows:
• Bores #1 to #6: 0.094 to 0.120 mm (0.0037 to 0.0047 in.)
• Bores #7 and #8: 0.107 to 0.133 mm (0.0042 to 0.0052 in.)
For service purposes, three sizes of pistons are available as follows:
• Service Standard (labeled JT)
• Service – High Limit (labeled GT)
• Service – 0.50 mm O.S. (labeled as 0.50 OST)
The JT piston size has a skirt diameter of 102.867 to 102.880 mm (4.0499 to 4.0504 in.) and fits in a cylinder with a bore diameter of 102.947 to 102.987 mm (4.05409 to 4.05461 in.).
The GT piston size has a skirt diameter of 102.906 to 102.919 mm (4.0514 to 4.0519 in.) and fits in a cylinder with a bore diameter of 103.013 to 103.026 mm (4.05563 to 4.05614 in.).
The 0.50 OST piston has a skirt diameter of 103.401 to 103.414 mm (4.0709 to 4.0714 in.) and fits in a cylinder with a bore diameter of 103.508 to 103.521 mm (4.07512 to 4.07563 in.).