Hot Rod Magazine, February 1957, 3rd page

Boring the cylinders in the block an eighth-inch oversize presented no problems because of the more than adequate thickness of their walls. From the apparent thickness of the waIls after the boring it looked as though the cylinders could have been enlarged at least another quarter of an inch without any trouble at all, however this is just speculation and not to be taken for the gospel truth.

The cylinders were finished to a diameter 0.008 of an inch larger than the top of the skirts of the Jahns three ring pistons that were to be fitted. Ring grooves in the pistons are 5/64 of an inch wide for the top and middle rings and 3/16 of an inch for the oil ring. Piston pins supplied with the pistons are stock diameter.

After the pistons were fitted to the cylinders their skirts were knurled to enlarge them a total of 0.006 of an inch. Knurling is a commercial process of creating hundreds of raised marks on the skirts of pistons to make the diameter of the skirts larger. Knurling helps stabilize a piston in its cylinder and when it has wom down to its working height it provides an additional benefit of reducing the friction of the skirt on the wall of the cyiinder. The piston pin bushing in the connecting rods and the pin holes in the pistons were honed to an easy push fit for the pins and then the rods and pistons were cleaned thoroughly and the pistons assembled on the rods. Conventional wire type locks retain the full floating pins in the pistons.

The piston and rod assemblies were aligned on an aligning fixture to bring the axis of the pistons into alignment with the vertical centerline of the rods. This is a necessary operation because it is possible for a rod to be bent or for the pin bore to be off slightly in a piston. Either of these conditions causes undue loads on the rod’s bearing and higher than normal friction between the piston and the walls of its cylinder.

As with most strokers, it was necessary to grind slots in the lawer end of each of the cylinders to provide clearance for the rod assembly in the cylinder directly opposite. In other words. the slots ground in one bank of cylinders were to provide clearance for the rods in the other bank. The exact spots for the slots were found by installing the crankshaft temporarily in the block and then inserting a rod and piston assembly,

less rings, in one of the cylinders of each bank and securing them to their respective crankpin,. The crankshaft was then rotated by hand and the spots where the ends of the cap retaining bolts and the lock nuts on the bolts hit the ends of the cylinders were marked. The rod and piston assemblies were removed irom the block and grooves were ground in the same relative location in the cylinders of both banks. The grooves were ground to a depth of approximately 1/4 of an inch and to a width of about 3/4 of an inch. There is plenty of material in the area where the slots must be ground so there is lirtle chance of grinding into the water jacket if one uses reasonable caution during the grinding.

After a thorough cleaning of its internal and external surfaces and the installation of new camshaft bearings. the block was ready to go.

The crankshaft was stroked with the regular C-T welding process that involves enlarging the crankpins by laying bead after bead of welding rod on them with an arc welder. The pins are then ground to size but on a new center to give the throws the desired stroke. The crankpins on the Packard shaft have large holes through their centers that caused one side of each of them to be somewhat thinner than the opposite side after they had been ground for the new stroke. This condition made the shaft something of an unknown quantity but from all indications the stroked pins are strong enough to carry the load because so far they haven't given any trouble under severe running conditions.

When the shaft's main bearing journals and crankpins were ground they were finished to diameters slightly smaller than the smaller diameter allowed by the factory tolerances. The theory behind the smaller journals and crankpins is to allow a bit more running clearance for the bearings than they would have if they were of the specified diameters and thereby permit a greater quantity of lubricatins oil to flow through them for better lubrication and cooling. If done in moderation. a slight amount of additional bearing clearance can be a good thing in an engine to be run mostly at high speed but if carried to an extreme additional clearance can lead to short bearing life and excessive oil consumption. The excessive oil consumption could result from the inability of the piston rings to control the greater quantities of oil that would be thrown onto the cylinder waIls

by the bearings as the crankshaft rotated.

Factory tolerance for the main bearing journals is from 2.500 inches for the larger diameter to 2.499 inches for the smaller diameter. However. to restore them to their original round condition. the journals were to be ground to the standard undersize of .010 of an inch. which would make the low side of the tolerance 2.489 inches to grind slots in the lawer end of each of the cylinders to provide clearance for the rod assembly in the cylinder directly opposite. In other words. the slots ground in one bank of cylinders were to provide clearance for the rods in the other bank. The exact spots for the slots were found by installing the crankshaft temporarily in the block and then inserting a rod and piston assembly, less rings, in one of the cylinders of each bank and securing them to their respective crankpin. The crankshaft was then rotated by hand and the spots where the ends of the cap retaining bolts and the lock nuts on the bolts hit the ends of the cylinders were marked. The rod and piston assemblies were removed irom the block and grooves were ground in the same relative location in the cylinders of both banks. The grooves were ground to a depth of approximately 1/4 of an inch and to a width of about 3/4 of an inch. There is plenty of material in the area where the slots must be ground so there is lirtle chance of grinding into the water jacket if one uses reasonable caution during the grinding.

To provide the desired additional clearance, the journals were finished to 2.488 inches. which is 0.001 of an inch smaller than the tolerance would allow for a 0.010 inch undersize journal. Tolerance for the crankpins is from 2.503 inches for the larger diameter to 2.249 inches for the smaller diameter. The pins were finished to 2.2490 inches. which is 0.0007 (seven ten thousandths) of an inch smaller than allowed by the low side of the tolerance. After the grinding was finished, the journals and pins were polished with a motor driven emery belt.

The entire crankshaft and connecting rod and piston assembly was balanced to precision tolerances on the specialized balancing equipment in C-T's shop. The parts that were balanced included the pistons, connecting rods, crankshaft, flywheel, and clutch pressure plate and cover.

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