Usage:
D346, D349 Truck Engines;
D348 Vehicular Engines
Description of Change: In an earlier change, the alternator drive pulleys and belts were changed to increase the alternator RPM. This change improved the charging characteristics at slow engine RPM, but the alternator drive belts had a shorter service life. Since battery charging is not a problem in most conditions of operation, the earlier alternator groups with a slower drive RPM are now used again for maximum belt service life.
At the same time, new vee belt sets are released for use on engines equipped with the faster RPM alternator. These are heavy duty belts, and will give longer service life than the former belts. The slower RPM alternators use single groove pulleys and one drive belt, in comparison with the faster RPM alternators which use double groove pulleys and a set of two drive belts.
Adaptable To: The new (slower RPM) alternator groups and the crankshaft drive pulley, used together, are directly adaptable to all earlier engines. The former (faster RPM) alternator groups are canceled and, if ordered, the new group and crankshaft drive pulley will be sent. If desired, conversion of a former alternator group to a new group can be made by installation of the new alternator pulley and drive belt. The new crankshaft drive pulley (part of the drive pulley and damper group) must also be used.
For engines equipped with the former (faster RPM) alternator groups, the new 7N3157 and 7N3158 Vee Belt Sets are each adaptable as a direct replacement for the former 3N6591 and 3N6589 Vee Belt Sets respectively. The former belt sets are canceled and, if ordered, the new belt set will be sent.