The new style rods, part # 114-0394, with a casting number of 170-4444A, B, C etc for the 16HP engines & part # 114-0397 with a casting number 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.
