The new style rods with a casting number of 170-4444A, B, C etc for the 16HP engines & Casting numbers of 170-4447A, B, C etc. for the 18-20HP engines have different weights compared to the early style rods If
you only need to replace one rod and it has the same casting number as
above then no problem.
But if you have the older style with different
casting numbers you must replace them in pairs to avoid an out of
balance engine. New style have a solid I-Beam and old style have a hole
in the I-beam near the big end. Common casting numbers on old style
rods that can not be mixed with new style are: 170-2429, 170-3439 etc. for the 16HP engines & 170-4105 A, B C etc.for the 18-20HP engines.
Old style rod pictured on the left & New style on the right.
