original size for these parts to maintain factory tolerances.Cutting away cylinder walls
The size and taper of the cylinders was also checked using a dial-bore
gauge adjusted in conjunction with a micrometer, and they were also
examined for an out-of-round condition. Herman used a tool to measure
the diameter of the cylinder in several areas at the top, bottom and
center. On average, this engine’s cylinders were .003 to .005 inches off,
a relatively small amount reflecting the fact the cylinders had never been
bored and the pistons didn’t cause excessive wear to the cylinder walls.
On this engine, a ridge remained at the top of the cylinder as the
pistons do not rise all of the way to the top of the cylinder. Where the
pistons do pass on the cylinder walls, they remove material through
years of rising and falling as the engine turns. To make the cylinder the
same diameter from top to bottom, this ridge will be bored down, as will
the remaining lower portion of the cylinder walls, to the same
dimension. Herman estimated he would need to bore the cylinders down
.020 inches to remove the ridge and scoring in each cylinder with a
boring machine. Not all of the scoring to the cylinder walls was removed
at this bore size, however, so he bored it to the next size of .030 inches.